Polonium-210 budget in cigarettes
Transcription
Polonium-210 budget in cigarettes
Journal of Environmental Radioactivity 71 (2004) 33–41 www.elsevier.com/locate/jenvrad Polonium-210 budget in cigarettes Ashraf E.M. Khater ∗ National Center for Nuclear Safety and Radiation Control, Atomic Energy Authority, P.O. Box 7551, Nasr City, Cairo 11762, Egypt Received 20 November 2002; received in revised form 1 March 2003; accepted 23 March 2003 Abstract Due to the relatively high activity concentrations of 210Po and 210Pb that are found in tobacco and its products, cigarette smoking highly increases the internal intake of both radionuclides and their concentrations in the lung tissues. That might contribute significantly to an increase in the internal radiation dose and in the number of instances of lung cancer observed among smokers. Samples of most frequently smoked fine and popular brands of cigarettes were collected from those available on the Egyptian market. 210Po activity concentrations were measured by alpha spectrometry, using surface barrier detectors, following the radiochemical separation of polonium. Samples of fresh tobacco, wrapping paper, fresh filters, ash and postsmoking filters were spiked with 208Po for chemical recovery calculation. The samples were dissolved using mineral acids (HNO3, HCl and HF). Polonium was spontaneously plated-out on stainless steel disks from diluted HCl solution. The 210Po activity concentration in smoke was estimated on the basis of its activity in fresh tobacco and wrapping paper, fresh filter, ash and post-smoking filters. The percentages of 210Po activity concentrations that were recovered from the cigarette tobacco to ash, post-smoking filters, and smokes were assessed. The results of this work indicate that the average (range) activity concentration of 210Po in cigarette tobacco was 16.6 (9.7–22.5) mBq/cigarette. The average percentages of 210Po content in fresh tobacco plus wrapping paper that were recovered by post-smoking filters, ash and smoke were 4.6, 20.7 and 74.7, respectively. Cigarette smokers, who are smoking one pack (20 cigarettes) per day, are inhaling on average 123 mBq/d of 210Po and 210Pb each. The annual effective doses were calculated on the basis of 210Po and 210Pb intake with the cigarette smoke. The mean values of the annual effective dose for smokers (one pack per day) were estimated to be 193 and 251 µSv from 210Po and 210Pb, respectively. 2003 Elsevier Ltd. All rights reserved. Keywords: Polonium-210; Lead-210; Cigarettes smoking; Tobacco; Radiation dose; Egypt ∗ Tel. and fax: +202-274-0238. E-mail address: [email protected] (A.E.M. Khater). 0265-931X/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0265-931X(03)00118-8 34 A.E.M. Khater / J. Environ. Radioactivity 71 (2004) 33–41 1. Introduction Polonium-210 (which has a physical half-life time of 138 days) is a member of the natural uranium-238 series and one of the relatively long-lived radionuclides of radon decay products. It is an alpha-emitting radionuclide and is present in trace amounts in most plants and foodstuffs as well as in human tissues (Batarekh and Teherani, 1987). The polonium isotopes are among the most radiotoxic nuclides to human beings. The concentrations of 210Po in cigarette tobacco are in the range of 2.8–37 Bq/kg and vary with the cigarette brand, probably due to the different varieties of tobacco used and to different manufacturing procedures (Skwarzec et al., 2001b). The results obtained by Radford and Hunt (1964) indicate that 210Po in cigarettes is volatilized at the temperatures characteristic for burning cigarettes and inhaled into the lung along with the cigarette smoke (mainstream smoke). It might effectively be a factor in the increased incidence of lung cancer among cigarettes smokers (Radford and Hunt, 1964). Since then, other investigators have studied both the sources and behavior of 210Po and 210Pb in relation to smoking, and the biological effects of these on lung tissues and other organs (Batarekh and Teherani, 1987; Black and Brethauer, 1968; Boltzman and Ilcewicz, 1966; Cohen, 1979a,b; Fletcher, 1994; Godoy et al., 1992; Karali et al., 1996; Martell, 1974; Mussealo-Rauhammaa and Jaakkola, 1985; Nada et al., 1999; Rajewskey and Stahlhofen, 1966; Shabana et al., 2000; Sinh and Nilekani, 1976; Tso et al., 1964; Tso et al., 1966; Watson, 1985). Tso et al. (1966) reported that the principal source of 210Pb and thus also of 210Po in tobacco is the soil and the contribution of polonium from atmosphere onto the tobacco plant to the total activity in the plant is minor compared to the polonium absorbed from the soil via the roots (Tso et al., 1966). In contrast Skwarzec et al. (2001b) indicated that the atmospheric deposition is the main source of 210Po in the tobacco leaves. It is known to be absorbed to sub-micron-sized particles present in the smoke. Lead-210 is not sublimated at this temperature, but is rather a component of the resulting smoke and ash (Watson, 1985). Lead is inhaled with the particulate fraction of mainstream smoke and acts as long-term source of 210Po exposure. Both radionuclides contribute to cancer risk due to their deposition in the tissue of the lungs (Fletcher, 1994; Karali et al., 1996; Martell, 1974; Watson, 1985). About 6.5–22% of the 210Po contained in cigarettes was found in the mainstream smoke (Mussealo-Rauhammaa and Jaakkola, 1985; Radford and Hunt, 1964). Other authors have reported different percentage values, ranging from 3.7 to 58%. On average, approximately 50% of the 210Po in cigarette tobacco is transferred to the smoke, 35% remains in the butt and approximately 15% is found in the ash (Parfenov, 1974). Numerous variables govern the degree of exposure via the pathway of tobacco smoke: the geographic region where the tobacco is grown, the fineness of the tobacco cut, the presence or absence of a filter, the size and composition of the filter and smoking habits (Watson, 1985). It has been reported that the content of other carcinogens in tobacco today has been greatly reduced by means of changes in tobacco processing methods and the use of modern cigarette filters, but these have little effect in terms of reducing radioactivity levels. Although, in the last few years, many studies have been carried out A.E.M. Khater / J. Environ. Radioactivity 71 (2004) 33–41 35 to investigate the reduction in trace element and other toxic substances in cigarettes achieved through the use of modern tobacco processing techniques and filter materials, only few studies have been carried out to investigate the reductions in radioactivity levels. This work was aimed in determining 210Po specific activity in most frequently smoked Egyptian cigarettes in order to estimate the annual effective dose to cigarettes smokers due to 210Po and 210Pb inhalation via smoking. This work is a part of the national program to estimate the radioactivity contents of consumer products. Due to a large-scale consumption of tobacco in Egypt at the present time, we found this study to be a necessity. Also, it is providing the first new data available since that of Black and Brethauer (1968). 2. Experimental work Ten samples of Egyptian produced fine and popular brands of most frequently smoked cigarettes in Egypt were randomly selected from those available on the market. Although each brand has several types of cigarettes, only the most popular one was chosen for analysis. Five cigarettes were taken from each pack to provide combined samples from different parts of the cigarettes, i.e. fresh tobacco, wrapping papers and fresh filters. A further five cigarettes were taken from the same pack and smoked by volunteer smokers to simulate the normal cigarette-smoking conditions. Tobacco ash and post-smoking filters were collected to provide the combined samples. Finally, we had 50 samples for 210Po (E a = 5.116 MeV) analyses. Samples of know weights (0.2–4.9 g) were spiked with 208Po (E a = 5.3045 MeV) tracer (at activities of about 100 mBq per sample) in order to calculate the chemical recovery. The samples were dissolved using three portions of a mixture of 40 ml HNO3 (65%) and 10 ml HF (40%), and evaporated to near dryness on a sand bath at a temperature of about 80 °C. The sample residuals were treated with two portions of 10 ml HCl (32%), and evaporated to near dryness. Finally, the samples were dissolved in 30 ml 0.5 M HCl. Polonium was spontaneously plated from the solution at temperatures between 80–90 oC onto rotating stainless steel disks fixed in a Teflon disk holder (Flynn, 1968; Hamilton and Smith, 1986). The plated disks were measured using alpha spectrometers (CANBERRA 4701 vacuum chambers), employing PIPS detectors with efficiencies ranged from 17 to 25% and an average resolution of 17 keV in 241Am alphas, and connected up to a computerized multi-channel analyzer operating with Genie 2000 software (CANBERRA). The samples were measured for 60,000 s. Minimum detectable activity (MDA), of 1 mBq, determined for the detection system and radiochemical procedures adopted in this study (Currie, 1968). The average chemical recovery was 75%, and the individual values ranged from 50 to 100%. Analytical quality control measurements were regularly performed through reference samples analyses (e.g. IAEA-326 and IAEA-327), blank samples analyses and participation in IAEA inter-comparison exercises. The uncertainties of the reported results are evaluated considering counting statistics and calibration error only. 36 A.E.M. Khater / J. Environ. Radioactivity 71 (2004) 33–41 3. Results and discussion The average (range of) activity concentrations of 210Po in cigarettes tobacco, wrapping paper, fresh filters, ash and post-smoking filters from fine and popular brands of the Egyptian cigarettes are presented in mBq/g and mBq/cigarette in Table 1. The activity concentrations of 210Po in mBq/cigarette present in the cigarette tobacco, wrapping paper, ash and post-smoking filters, and the smoke, and the percentages of 210Po recovered in cigarettes ash, post-smoking filters and smoke are presented in Table 2. The average activity concentrations of 210Po in fine and popular brand cigarette tobacco were 12.6 ± 1.7 and 19.9 ± 2.7 mBq/cigarette, respectively (Table 1). Since the analyzed cigarette brands represent the most frequently smoked cigarettes and about 80% of the Egyptian cigarette market, the average activity concentration of 210 Po in the fresh tobacco of the Egyptian cigarettes is 16.3± 3.2 mBq/cigarette (21.0 ± 4.0 mBq/g). The efficiency of cigarettes filters to reduce the smoke content of polonium is proved to be quiet low in both brands. The average values are 4.7% and 4.5% of the 210Po contained in the fresh tobacco plus wrapping paper for fine brand and popular brand cigarettes, respectively [Table 2(b)]. The risks associated with cigarette smoking is due not only to high concentrations of toxic substances, but also to the poor efficiency of the filters, which do not reduce sufficiently the quantities of carcinogenic substances contained in cigarette smokes (Skwarzec et al., 2001a). The average 210Po activity concentration percentages recovered in fine and popular brands cigarette ash were 17.1% and 24.3%, respectively. From these results, it was concluded that the activity concentrations of 210Po in popular brands of cigarettes is higher in tobacco and smokes than those in fine brands of cigarettes. Table 1 The average activity concentrations ±1σ (range) of 210Po (mBq/g & mBq/cigarette) in fine and popular brands of Egyptian cigarettes (fresh and post smoking) Samples (a) mBq/g Fine brand Popular brand Tobacco Wrapping paper Filter Cigarette ash Post-smoking filter 17.8 ± 2.3 (14.8–20.9) 8.1 ± 4.1 (4.6–10.9) 5.2 ± 1.9 (0.7–10.0) 20.2 ± 5.4 (16.1–3.9) 7.6 ± 2.8 (5.9–9.4) 24.2 ± 3.3 (21.8–27.2) 6.2 ± 3.6 (2.5–12.5) 9.7 ± 3.0 (1.2–22.5) 35.2 ± 6.8 (32.7–6.7) 12.6 ± 2.7 (9.8–16.9) 7.2 ± 5.5 7.5 ± 3.6 27.7 ± 8.7 10.1 ± 3.9 0.3 ± 0.2 (0.2–0.5) 0.9 ± 0.3 (0.1–1.7) 2.2 ± 0.6 (2.0–2.5) 1.5 ± 0.5 (1.2–1.9) Average 21.0 ± 4.0 (b) mBq/cigarette Fine brand 12.6 ± 1.7 (9.7–15.2) Popular brand 19.9 ± 2.7 (17.4⫺22.5) 0.3 ± 0.1 (0.1⫺0.6) 1.7 ± 0.5 (0.2⫺4.5) 4.9 ± 0.9 (4.1⫺5.8) 2.6 ± 0.6 (1.9⫺4.3) Average 16.3 ± 3.2 0.3 ± 0.2 1.3 ± 0.6 3.6 ± 1.1 2.1 ± 0.8 A.E.M. Khater / J. Environ. Radioactivity 71 (2004) 33–41 37 Table 2 (a) The average activity concentrations of 210Po (mBq/cigarette) in tobacco plus wrapping paper, ash plus post-smoking filters, and the smoke. (b) Percentages of 210Po activity concentrations recovered after cigarette smoking in cigarette ash, post-smoking filters and smoke (a) Samples Fine brand Popular brand Average Tobacco plus wrapping papers Ash plus post-smoking filters Smokea (b) 210Po %b Ash Post-smoking filters Smoke 12.9 ± 1.7 2.8 ± 0.8 10. 1 ± 1.9 20.2 ± 2.7 5.8 ± 1.2 14.4 ± 3.0 16.6 ±3.2 4.3 ± 1.4 12.3 ± 3.6 17.1 4.7 78.2 24.3 4.5 71.2 20.7 4.6 74.7 a (Activity concentration in fresh tobacco plus wrapping paper)⫺(activity concentration in ash plus post-smoking filter). b Percentages were calculated based on the activity in ash, post-smoking filters and smokes to activity in fresh tobacco plus wrapping paper (mBq/cigarette). The relatively low 210Po activity measured in the analyzed cigarette ash is due to volatilization of polonium at the cigarette burning temperature (600–800 oC), which is partially inhaled by the smoker (Radford and Hunt, 1964; Skwarzec et al., 2001a). On average, about 25% of the total polonium in the cigarette tobacco was retained in the cigarette filter and ash. About 75% of the polonium content in the cigarette tobacco was contained in the cigarette smoke, which is partially inhaled and deposited in the lung tissues. Average activity concentrations for 210Po (in mBq/cigarette) in Egyptian cigarettes and those from other countries are shown in Table 3. These data indicate that 210Po concentrations ranged from 3.3 mBq/g (about 4 mBq/cigarette, based on a normal value for cigarette weight) in India cigarettes to a maximum value of 23.2 mBq/cigarette in the French cigarettes. There is no significant difference between the results obtained by Black and Brethauer (1968) and our results. This means that the modern tobacco processing methods and filter materials used and developed over the last 32 years have not been sufficient to reduce the 210Po concentrations in cigarette tobacco and smoke. Activity concentration of 210Po (210Pb) in Egyptian cigarettes tobacco (mBq/cig.) and inhaled via smoking per day (mBq/d) and year (mBq/yr) and annual committed effective dose (µSv/yr) due to 210Po and 210Pb inhalation via smoking are shown in Table 4. On account of the time interval between the harvesting of tobacco leaves and cigarettes production (often more than 2 yr), about six to seven half-lives of 210 Po, 210Po in cigarette tobacco approaches a secular equilibrium with 210Pb (Godoy et al., 1992; Carvalho, 1995; Skwarzec et al., 2001a; Peres and Hiromoto, 2002). Assuming that 50% of the total 210Po and 210Pb activity concentrations in cigarette smoke is inhaled during smoking (Skwarzec et al., 2001a), it means that for a smoker consuming one pack (20 cigarettes) per day, the average activity concentrations of both 210Po and 210Pb intake with cigarette smoke will thus be 202 mBq for fine b a 22.4 8.6 23.2 10.7 14.1 14.3 Japan Norway France Philippines Russia Turkey and and and and and Brethauer Brethauer Brethauer Brethauer Brethauer In mBq/g. Assuming 1.2 g tobacco per cigarette. Black and Brethauer Black and Brethauer Black and Brethauer Black and Brethauer Black and Brethauer Karali et al. (1996) Black Black Black Black Black 17.3 7.9 14.1 10.8 19.2 England Canada Egypt Finland Germany (1968) (1968) (1968) (1968) (1968) (1968) (1968) (1968) (1968) (1968) India Poland Brazil Egypt Egypt Various Czechoslovakia Brazil Bulgaria Finland Country Po 3.3a(3.96)b 13.3 21.2a(25.4)b 16.3 21.0a 18.1 11.7 16.9 14.0 11.1 210 Parfenov (1974) Parfenov (1974) Parfenov (1974) Parfenov (1974) Mussealo-Rauhammaa and Jaakkola (1985) Sinh and Nilekani (1976) Skwarzec et al. (2001a,b) Peres and Hiromoto (2002) This study This study Ref. Po in Egyptian cigarettes and in those from other countries, expressed in mBq/cigarette Ref. 210 Country Table 3 The average activity concentrations of 38 A.E.M. Khater / J. Environ. Radioactivity 71 (2004) 33–41 A.E.M. Khater / J. Environ. Radioactivity 71 (2004) 33–41 39 Table 4 Activity concentration of 210Po in Egyptian cigarette tobacco (mBq/cig.) and inhaled via smoking per day (mBq/d) and year (mBq/yr) and annual committed effective dose (µSv/yr) due to 210Po and 210Pb inhalation via smoking Po-210 activity concentration mBq/cig. Fine brand 10.1 Popular brand 14.4 Average 12.3 a b c Annual committed effective dose (µSv/yr) mBq/da Bq/yr Po-210b Pb-210c Total 101 144 123 36.9 52.6 44.9 159 226 193 207 295 251 366 521 444 20 cigarette/day and 50% of 210Po (210Pb) in smoke inhaled. 4.3 µSv/Bq, 210Po dose conversion factor. Assuming 210 Po and 210Pb are in secular equilibrium & 210Pb dose conversion factor =5.6 µSv/Bq. brand cigarettes and 288 mBq for popular brand cigarettes. These values may change depending on the number and size of puffs per cigarette (smoking habits), and 210Po and 210Pb concentrations in the non-inhaled side smoke. By applying the dose conversion factor for adults of 5.6 µSv/Bq for 210Pb and 4.3 µSv/Bq for 210Po (Peres and Hiromoto, 2002), the average annual committed effective dose is estimated to be an average 193 and 251 µSv due to cigarettes smoking for 210Po and 210Pb, respectively. 4. Conclusions Cigarette smoking increases the internal intake of 210Po and 210Pb, which are contained in cigarette tobacco in relatively high concentrations. Polonium-210 and 210Pb that are inhaled and deposited in the lung tissues will contribute to an increase in the internal radiation dose and in the number of lung cancer incidences observed among smokers. The results of this work indicate that the average activity concentration of 210Po in Egyptian cigarettes tobacco is 16.3 mBq/cigarette, with a range of 9.7–22.5 mBq/cigarette. Since these results are comparable to results of Black and Brethauer (1968), we can conclude that the modern tobacco processing methods have not effectively reduced the average content of 210Po in Egyptian cigarette tobacco. The activity concentrations of 210Po in popular brand cigarette tobacco and smoke are higher than that in fine brand cigarette tobacco. The efficiency of cigarette filter to reduce the 210Po activity in cigarette smokes is quiet low, an average 4.6 % of the 210Po contained in the cigarette tobacco. The average recovery percentages of the 210Po contained in cigarette tobacco to cigarette ash and smoke are 20.7% and 74.7%, respectively. Based on the average activity concentration of 210Po recovered in cigarette smoke (12.3 mBq/cigarette) and assuming that 50% of 210Po and 210Pb activity contained in cigarette smoke is inhaled, the average committed effective doses due to 210Po and 210Pb intake by smoking one pack of cigarettes per day, during 1 yr, are 0.19 and 0.25 mSv, respectively. 40 A.E.M. Khater / J. Environ. Radioactivity 71 (2004) 33–41 Acknowledgements I wish to express my deep gratitude to Dr. Max Pimpl for reviewing the manuscript. The author wish to acknowledge the support received from the International Bureau of Forschungszentrum Julich in Germany. References Batarekh, K., Teherani, D.K., 1987. Determination of polonium-210 in cigarettes from Syria. Journal of Radioanalytical Nuclear Chemistry Letters 117 (2), 75–80. Black, S.C., Brethauer, E.W., 1968. Polonium-210 in tobacco. Radiological Health Data and Report, March, 145–152. Boltzman, R.B., Ilcewicz, F.H., 1966. 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Godoy, J.M., Gouveu, V.A., Mello, D.R., Azeredo, M.G., 1992. 226Ra/210Pb/210Po equilibrium in tobacco leaves. Radiation Protection Dosimetry 45 (1-4), 299–300. Hamilton, T.F., Smith, J.D., 1986. Improved alpha energy resolution for the determination of polonium isotopes by alpha-spectrometry. Applied Radiation and Isotopes 37 (7), 628–630. Karali, T., Ole, S., Veneer, G., 1996. Study of spontaneous deposition of 210Po on various metals and application to activity assessment in cigarette smoke. Applied Radiation and Isotopes 47 (4), 409–411. Martell, T.F., 1974. Radioactivity of tobacco trichomes and insoluble cigarette smoke particles. Nature 249, 215–217. Mussealo-Rauhammaa, H., Jaakkola, T., 1985. Plutonium-239, 240Pu and 210Po content of tobacco and cigarette smoke. Health Physics 49 (2), 296–301. Nada, A., Abdel Wahab, M., Sroor, A., Abdel-Haleem, A.S., Abel-Sabour, M.F., 1999. Heavy metal and rare earth elements source—sink in some Egyptian cigarettes as determined by neutron activation analysis. Applied Radiation and Isotopes 51, 131–136. Parfenov, Yu.D., 1974. Polonium-210 in the environment and in the human organism. Atomic Energy Review 12, 75–143. Peres, A.C., Hiromoto, G., 2002. Evaluation of 210Pb and 210Po in cigarette tobacco produced in Brazil. Journal of Environmental Radioactivity 62, 115–119. Radford, E., Hunt, V.R., 1964. Polonium-210: a volatile radioelement in cigarette. Science, 143, 247–249. Rajewskey, B., Stahlhofen, W., 1966. Polonium-210 activity in the lungs of cigarette smokers. Nature 209, 1312–1313. Shabana, E.I., Abd Elaziz, M.A., Al-Arifi, M.N., Al-Dhwailie, A.A., Al-Bokari, M.M., 2000. Evaluation of the contribution of smoking to total blood Polonium-210 in Saudi population. Applied Radiation and Isotopes 52, 23–26. Sinh, D.R., Nilekani, S.R., 1976. Measurement of polonium activity in Indian tobacco. Health Physics 31, 393–394. A.E.M. Khater / J. Environ. Radioactivity 71 (2004) 33–41 41 Skwarzec, B., Ulatowski, J., Struminska, D.I., Borylo, A., 2001a. Inhalation of 210Po and 210Pb from cigarette smoking in Poland. Journal of Environmental Radioactivity 57, 221–230. Skwarzec, B., Struminska, D.I., Ulatowski, J., Golebiowski, M., 2001b. Determination and distribution of 210Po in tobacco plants from Poland. Journal of Radioanalytical and Nuclear Chemistry 250 (2), 319–322. Tso, T.C., Hallden, N.A., Alexander, L.T., 1964. Radium-226 and polonium-210 in leaf tobacco and tobacco soil. Science 146, 1043–1045. Tso, T.C., Harley, N., Alexander, L.T., 1966. Source of lead-210 and polonium-210 in tobacco. Science 153, 880–882. Watson, A.P., 1985. Polonium-210 and lead-210 in food and tobacco products: transfer parameters and normal exposure and dose. Nuclear Safety 26 (2), 179–191. Journal of Environmental Radioactivity 55 (2001) 255–267 Radiological impacts of natural radioactivity in Abu-Tartor phosphate deposits, Egypt Ashraf E.M. Khatera,*, R.H. Higgya, M. Pimplb a National Center for Nuclear Safety and Radiation Control, P.O. Box 7551, Nasr City 11762, Cairo, Egypt b Central Safety Department, Forschungszentrum Karlsruhe, D-76021 Karlsruhe, Germany Received 15 October 1999; received in revised form 1 July 2000; accepted 21 July 2000 Abstract Phosphate and environmental samples were collected from Abu Tartor phosphate mine and the surrounding region. The activity concentration of 226Ra (238U) series, 232Th series and 40K were measured using a gamma-ray spectrometer. The activities of uranium isotopes (238U, 235 U and 234U) and 210Pb were measured using an alpha spectrometer and a low-background proportional gas counting system, respectively, after radiochemical separation. The results are discussed and compared with the levels in phosphate rocks from different countries. It seems that the Abu Tartor phosphate deposit has the lowest radioactivity level of exploited phosphate of sedimentary origin. 226Ra/238U, 210Pb/226Ra, 234U/238U and 226Ra/228Ra activity ratios were calculated and are discussed. The radioactivity levels in the surrounding region and the calculated exposure dose (nGy/h) will be considered as a pre-operational baseline to estimate the possible radiological impacts due to mining, processing and future phosphate industrial activities. To minimize these impacts, the processing wastes should be recycled to the greatest possible extent. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Radioactivity; Abu Tartor; Phosphate rocks; Phosphate mining and processing; Dose assessment 1. Introduction Phosphate rock is the starting raw material for all phosphate products. It can be of sedimentary, volcanic or biological origin. Concentrations of 232Th series and 40K in phosphate rocks of all types are similar to those observed normally in soil, whereas *Corresponding author. Tel./fax: +202-274-0238. E-mail address: [email protected] (A.E.M. Khater). 0265-931X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 5 - 9 3 1 X ( 0 0 ) 0 0 1 9 3 - 4 256 A.E.M. Khater et al. / J. Environ. Radioactivity 55 (2001) 255–267 the concentration of 238U and its decay products tend to be elevated in phosphate deposits of sedimentary origin. A typical concentration of 238U in sedimentary phosphate deposits is 1500 Bq/kg (UNSCEAR, 1993). Investigators have reported a wide variation in the concentrations of uranium and radium in phosphate rocks from various parts of the world. For uranium a range from 3 to 400 ppm, corresponding to 37–4900 Bq 238U/kg (1 ppm U=12.23 Bq 238U/kg) and for 226Ra a range from 100 to 10,000 Bq/kg are reported (Rossler, Smith, Bolch & Prince, 1979; IAEA 1979). It is widely believed that the radioactivity associated with phosphate rocks of sedimentary origin is formed by the adsorption and co-precipitation of uranium with calcium. Several investigators have indicated that, in general, the radionuclide content of a phosphate deposit increases with increasing P2O5 (Guimond, 1990). Due to the similarity in ionic size between U4+ (0.99Å) and Ca (0.89Å), the tetravalent uranium can readily enter the apatite structure. While the uranyl (U6+) is much larger, it can only be fixed in the exterior part of the structure by various adsorption processes. The presence of tetravalent uranium implies strongly reducing organic mud in which apatite is formed. Hexavalent uranium exists under more oxidizing post-sedimentary conditions that occur generally during emergence (Giresse, 1986). The primary potential environmental radiation problem associated with phosphate rock mining and processing concerns mining spoils and processing waste products. While these materials do not present a direct radiation hazard, problems may be created by their use. Occupational exposures mainly occur during mining, processing and transportation of phosphate rock, as well as during transportation and utilization of phosphate fertilizers (UNSCEAR, 1988). 1.1. Abu-Tartor phosphate mine 1.1.1. Geological features Abu-Tartor plateau forms a part of the rugged stretch that separates Dakhla and Kharga Oases in the Western Desert of Egypt. The plateau has an area of about 1200 km2. The geological section in this area includes (from bottom to top) the Nubian formation, phosphate formation, Dakhla formation and Kurkur formation (Hermina & Wassef, 1975; Bahay, Youssef Hassan & Abd El Nabi Atti Saad, 1978). 1.2. Phosphate mining and beneficiation Abu-Tartor mine is a close cast mine. The current reserve estimate in the exhaustively investigated area is in the order of a billion tons of phosphate ore (Said, 1990). The planned ore rock annual production is 4 million tons which will be processed to produce 2.2 million tons per year of wet rocks. In the purification process, the ore rocks are crushed, sieved and transferred to the processing plant. In the processing plant, the ore rocks are washed, wet screened and flotationseparated to produce wet rocks and different rejects. The latter include primary hand pick-up (clay and dolomite rocks), wet screening, magnetic separation and slime (clay suspension). The magnetic separation and primary rejects are returned A.E.M. Khater et al. / J. Environ. Radioactivity 55 (2001) 255–267 257 Fig. 1. The steps of processing and material balance for Abu–Tartor phosphate mine (production, ton/yr, P2O5% and production %), (personal communication). back to the land. The slime is pumped to impoundment. The wet rocks are stocked in large open piles for sale or transport to a phosphate chemical plant. Water is recycled to the greatest possible extent. The steps involved in processing and material balance for Abu-Tartor mine are shown in Fig. 1 (personal communication). 2. Experimental work 2.1. Sampling and samples preparation Twenty-one phosphate and environmental composite samples were collected from Abu-Tartor phosphate mine and the surrounding region in March 1997. Seven phosphate samples were collected, including ore rocks, wet rocks, primary rejects (clay and dolomite rocks), wet screening rejects, magnetic separation rejects and slime. All phosphate samples (except the ore rock sample) were collected from the processing pilot plant. Five soil samples were collected from cultivated and uncultivated land: two from a major farm, two from a newly reclaimed farm (new farm), and one from a future farm (uncultivated). The future farm is closer to the mine than the other two farms. Three samples of underground water and two samples of recycled water (from the processing pilot plant) were collected. In the mine region there are 13 underground water wells. Most of their water is pumped into a pipe network to the treatment station for public use, the processing plant and agriculture purposes. The underground water well near the new farm (well 258 A.E.M. Khater et al. / J. Environ. Radioactivity 55 (2001) 255–267 number 13) is used directly for agriculture purposes. Some of the water from the beneficiation plant will be used for irrigation of the future farm. Also, five plant samples were collected, two from the main farm and three from the new farm. Plants species are shown in Table 2. Because of the limited number of samples, great care were taken to have composite samples which should be representative of sample types and locations (USDOE, 1992). The soil samples were collected using a template of 25 25 cm2 with a depth of 5 cm. The water samples were collected and acidified to pH 1–2 by adding nitric acid to prevent the microbial growth and the interaction with the container walls (USDOE, 1992). Phosphate, soil and plant samples were dried at 1108C, mechanically crushed, mixed and sieved through a 2 mm mesh. For uranium and lead analysis a portion of the dried samples was moistened with concentrated nitric acid, fumed off to dryness, and ashed at 5508C for 12 h. The organic matter content was estimated as loss after ignition at 5508C. The water samples (about 5 l each) were evaporated to 1 l (USDOE, 1992; Sam, Mustafa, El Khangi, El Nigumi, & Holm, 1999). 2.2. Analytical methods 2.2.1. Gamma-spectrometric analysis Portions of the dried samples were transferred to Marinelli beakers of 1000 ml volume and sealed for about 4 weeks to reach secular equilibrium between radium and thorium and their progenies. The water samples were transferred to Marinelli beakers of 1000 ml volume. 226Ra (238U) series, 232Th series, and 40K activities were measured using gamma-spectrometry based on hyper-pure germanium detectors. The gamma transmissions used for activity calculations are 351.9 (214Pb), 609.3, 1120.3 and 1764.5 keV (214Bi) for the 226Ra series, 338.4, 911.1 and 968.9 keV (228Ac) for the 232Th series and 1460.7 keV for 40K. The gammaspectrometers were calibrated using both 226Ra point source and potassium chloride standard solutions in the same geometry as the samples (El-Tahawy, Farouk, Hammad, & Ibrahim, 1992). 2.2.2. Uranium isotope analysis Ashed samples (1–5 g) were spiked, for chemical recovery and activity calculations, with 232U tracer and dissolved using mineral acids (HNO3, HF and HCl). Uranium was extracted with trioctylphosphine oxide in cyclohexane, back-extracted with NH4F/HCl solution, then co-precipitated with La(NO3)3 and purified by passing through an anion exchange column. Uranium was then electroplated on a stainless-steel disk from oxalate–chloride solution. The prepared samples were measured using alpha-spectrometry based on surface barrier detectors with 450 mm2 surface area, about 17% efficiency and about 20 keV resolution. The chemical recovery was in the range from 45 to 70%. The lower detection limit of the procedure is in the range of 1 mBq/sample (measuring time=1000 min) (Pimpl, 1994). 259 A.E.M. Khater et al. / J. Environ. Radioactivity 55 (2001) 255–267 2.2.3. Lead-210 analysis Five grams of ashed samples were spiked with Pb2+ carrier and leached with 3 M HBr as tetrabromo-complex. This lead complex was extracted with trioctylamine/ toluene and back-extracted with concentrated HCl. After Bi separation as BiOCl precipitation, Pb was precipitated as PbCrO4 and collected on a filter paper. After waiting for about 8–10 days, the precipitate was covered with another filter paper of equal size and density (7–9 mg/cm2), to hold back the low-energy beta radiation of 210 Pb and the alpha radiation of ingrown 210Po. The beta radiation of the daughter product 210Bi was measured using a calibrated low-background alpha/beta gas proportional counter. The lower detection limit of the procedure is in the range of 150 mBq/sample (measuring time=1000 min). Activity concentrations of 210Pb were calculated from the activities of the daughter product 210Bi. The chemical recovery ranged from 50 to 100% (Pimpl, Yoo & Yordanov, 1992). Quality control of the measurements was performed by measuring background, blank, and reference samples on a regular basis, as well as participating in some international and regional quality control intercomparison exercises (IAEA, 1989). To compare the activity concentrations of materials containing 226Ra, 232Th and 40 K, the radium-equivalent activity is used to obtain the sum of those activities. The radium-equivalent activities have been calculated based on the estimation that 370 Bq 226Ra/kg, 259 Bq 232Th/kg and 4810 Bq 40K/kg produce the same gamma-ray dose rate. Therefore, the radium-equivalent activity of a sample can be written as Ra eq ¼ARa þ 1:43Ath þ 0:077AK ; where ARa; Ath , and AK are the activities of respectively (Hussein, 1994). 226 Ra, 232 Th and 40 K in Bq/kg, 3. Results and discussion The activities of the 226Ra (238U) series, 232Th series, 40K, 210Pb and radiumequivalent activity in Bq/kg dry weight and organic matter contents in phosphate and environmental samples are given in Tables 1 and 2, respectively. It is obvious that the main radioactivity content of phosphate rocks is due to 238U and its decay products. In the purification process, the changes in radioactivity contents could be due to mechanical separation of radionuclides between the wet rocks and the different rejects and/or solubility of radionuclides. The activities of 226 Ra in ore and wet rocks were not disturbed by the purification process, maybe, because Ra2+ is only moderately soluble in natural water (Ritcey, 1990). The elevation of radium content in the magnetic separation reject could be due to its adsorption by hydrous oxides of Fe(III) and/or Mn(IV) (Bowen, 1979). The activity concentration of 226Ra in the primary rejects (clay and dolomite rocks) is less than that of phosphate rock and comparable to the published values for sedimentary rocks (Ritcey, 1990). There are no differences in 232Th series activities, except for the primary rejects (dolomite rocks), that may be due to the poor solubility of thorium. The differences in 40K contents in wet rock and the 260 A.E.M. Khater et al. / J. Environ. Radioactivity 55 (2001) 255–267 Table 1 Activity concentrations of 226Ra series, 232Th series, 40K, 210Pb and radium equivalent in Bq/kg dry weight and organic matter content in phosphate samplesa Sample code and description 226 232 40 210 P1 P2 P3 P4 P5 P6 P7 284 5.1 287 3.6 228 2.5 241 3.7 190 4.7 59.4 1.2 70.7 0.8 23.7 2.8 23.7 2.3 22.4 1.3 24.9 2.4 24.9 3.1 28.7 1.6 14.9 0.6 45.9 8.4 21.4 4.1 71.8 3.6 17.6 4.3 28.8 7.3 297 3.3 229 2.2 259 2.7 224 1.9 286 3.3 299 2.8 120 1.3 44.4 0.9 67.3 1.0 a Ore rock Wet rock Wet screening Magnetic separation rejects Slime Primary rejects (clay) Primary rejects (dolomite) Ra E Th E KE Pb E Radium Equi. O.M.% 321 323 266 278 228 123 110 2.71 1.94 3.30 2.83 1.28 0.88 0.99 Maximum and minimum values are bold. Table 2 Activity concentrations of 226Ra series, 232Th series, 40K, 210Pb and radium equivalent in Bq/kg dry weight and organic matter content in environmental samplesa Sample code and description Soil samples S1 Main farm (east side) S2 Main farm (west side) S3 New farm (cultivated land) S4 New farm (uncultivated land) S5 Future farm Average Plant samples Pl 1 Gasuarina equestifoliab Pl 2 Gasuarina equestifoliab Pl 3 Gasuarina equestifoliac Pl 4 Eruca sativac Pl 5 Trifoliumc Average Water samples W1 Well 13 W2 Raw water W3 Raw water treated W4 Recycled water Average 226 232 40 27.8 0.6 32.8 1.0 19.0 1.3 27.7 0.6 21.4 0.6 25.7 1.9 44.2 0.8 41.5 1.1 17.6 0.6 24.8 0.7 16.8 0.7 29.0 1.8 74.5 0.9 152 3.1 127 2.8 163 2.1 127 2.0 129 5.2 8.0 0.7 5.1 0.9 2.8 0.4 3.6 0.6 8.2 2.0 5.5 2.4 Bq/l 50.6 50.6 50.6 50.6 } 50.7 50.7 50.7 50.7 50.7 } 457 7.0 752 8.3 802 7.0 1220 10.3 1848 15.5 1016 22.7 50.7 50.7 50.7 50.7 } 1.2 0.1 2.5 0.2 1.4 0.1 0.7 0.3 1.5 0.4 Ra E Th E KE 210 Pb E Radium equi. OM % 14.0 0.7 17.4 0.6 15.1 0.8 18.3 0.8 17.2 0.7 16.4 1.6 96.7 104 53.9 75.7 55.2 77.1 0.73 0.63 0.79 0.80 0.65 0.72 a Maximum and minimum values are bold. Main farm. c New farm. b processing rejects (excluding the primary rejects) could be due to the high solubility of potassium, the organic matter content and the particle size which corresponds to the clay content (Horrison, 1992). The radium-equivalent activities for phosphate samples have the same trend as 226Ra where 226Ra is very A.E.M. Khater et al. / J. Environ. Radioactivity 55 (2001) 255–267 261 high compared to 232Th and 40K, except for the primary rejects (clay and dolomite rocks). The activities of the 226Ra series, 232Th series and 40K in the soil samples are comparable and within the range reported for Egypt and other countries (UNSCEAR, 1988; Ibrahiem, Abd El Ghani, Shawky, Ashraf, & Farouk, 1993). For plant samples, 226Ra series and 232Th series activities are below the minimum detection limit (0.6 and 0.7 Bq/kg, respectively, for a measuring time of 8 h). The typical levels of 226Ra in most components of the diet range from 4 to 200 Bq/kg (Simon & Ibrahim, 1990). For water samples, 226Ra and 232Th and their decay products are below the minimum detection limits (0.6 and 0.7 Bq/l, respectively, for a measuring time of 8 h) in all samples. The activities of 238U, 235U and 234U in Bq/kg dry weight and uranium equivalent in ppm in phosphate and environmental samples are given in Table 3. The variation of uranium activities in phosphate samples could be due to the P2O5 percentage and the uranium solubility under oxidizing conditions (Guimond, 1990; Ivanovich & Table 3 Activity concentrations of uranium isotopes (238U, 235U and 234U) in Bq/kg dry weight and uranium equivalent in ppm in phosphate and environmental samples (1 ppm U=12.23 Bq 238U/kg)a Sample code and description 238 Phosphate samples (Bq/kg dry weight) P1 Ore rock P2 Wet rock P3 Wet screening P4 Magnetic separation rejects P5 Slime P6 Primary rejects (clay) P7 Primary rejects (Dolomite) Soil samples S1 Main farm (east side) S2 Main farm (west side) S3 New farm (cultivated land) S4 New farm (uncultivated land) S5 Future farm Average Plant samples Pl 1 Gasuarina equestifoliab Pl 2 Gasuarina equestifoliab Pl 3 Gasuarina equestifoliac PL 4 Eruca sativac Pl 5 Trifoliumc Average 371 20.0 408 23.5 210 6.8 437 31.8 192 12.1 42.3 2.4 56.9 2.7 a 234 Uranium equivalent 13.6 2.0 16.0 2.3 7.7 2.0 5.9 1.9 14.1 51.41 51.45 373 27.4 393 31.1 198 9.6 398 41.8 180 17.9 45.1 2.9 55.6 3.5 30.3 33.4 17.2 35.7 15.7 3.5 4.7 21.5 1.3 20.8 2.7 17.1 1.1 25.2 1.7 24.1 1.4 21.7 3.9 50.39 50.45 50.40 1.8 0.4 50.42 } 22.3 1.8 19.0 1.5 16.6 2.3 23.3 2.1 25.8 1.9 21.4 4.3 1.8 1.7 1.4 2.1 2.0 1.8 0.64 0.09 0.69 0.09 1.93 0.13 0.96 0.18 0.73 0.12 0.99 0.28 50.1 50.1 50.1 50.1 50.1 } 0.58 0.09 0.84 0.10 1.22 0.20 0.93 0.17 0.61 0.14 0.84 0.33 0.9 1.2 0.63 0.97 0.83 0.91 UE Maximum and minimum values are bold. Main farm. c New farm. b 235 UE UE 262 A.E.M. Khater et al. / J. Environ. Radioactivity 55 (2001) 255–267 Harmon, 1992). We could not find a clear relation between uranium concentrations and organic matter contents. The differences in the activities of the uranium isotopes (238U, 235U and 234U) in soil samples are not large, especially when the statistical errors are considered. However, it seems that the uranium activities in uncultivated lands are slightly higher than those in cultivated lands. This depletion of uranium in cultivated land due to soil reclamation process has been expected. The soil is mostly sandy with high permeability, typical for the region under investigation. Soil reclamation processes include soil washing which leads to leaching of some salt content and leaching of uranium. This effect is diminished with increasing content of organic material and clay in the cultivated soil. The activity ratios of 226Ra/238U, 210Pb/226Ra, 234U/238U and 226Ra/ 228Ra in phosphate and soil samples are given in Table 4. The 210Pb/226Ra activity ratios in ore rocks and primary rejects (dolomite rocks) are close to unity (0.91 and 0.95, respectively). In contrast, the ratios in wet screening and magnetic separation rejects are more than unity and in the other phosphate and soil samples they are less than unity, with an average of 0.66 in soil samples. This implies disequilibrium between the two radionuclides in some phosphate and soil samples. To explain the differences in the activity ratios of 210Pb/226Ra, we should remember that 226Ra is decaying to 222Rn gas which usually escapes from the matrix (soils and some geological formations) depending on the porosity of the matrix. In the case of rocks with no porosity, the 222Rn gas is enclosed inside the rocks and decays there, thus maintaining the equilibrium condition of the series. The mobility of the radon isotopes is regarded as one of the main causes of disequilibrium in the uranium decay series. The disequilibrium of the uranium and thorium series could be interpreted on the basis that if the activity of a daughter radionuclide is deficient relative to its Table 4 Activity ratios of 226 Ra/238U, 210 Pb/226Ra, 234 U/238U and Ra/228Ra in phosphate and soil samplesa Sample code and description 226 210 234 226 P1 Ore rock P2 Wet rock P3 Wet screening P4 Magnetic separation rejects P5 Slime P6 Primary rejects (clay) P7 Primary rejects (dolomite) Soil samples S1 Main farm (east side) S2 Main farm (west side) S3 New farm (cultivated land) S4 New farm (uncultivated land) S5 Future farm Average 0.77 0.70 1.09 0.55 0.99 1.40 1.24 0.91 0.78 1.26 1.24 0.63 0.75 0.95 1.01 0.96 0.94 0.91 0.94 1.07 0.98 12.5 12.5 10.0 10.0 7.7 2.1 4.8 1.29 1.58 1.11 1.1 0.89 1.19 0.50 0.53 0.79 0.66 0.81 0.66 1.04 0.91 0.97 0.92 1.07 0.99 a Ra/238U 226 Maximum and minimum values are bold. Pb/226Ra U/238U Ra/228Ra 0.63 0.79 1.08 1.11 1.27 0.98 A.E.M. Khater et al. / J. Environ. Radioactivity 55 (2001) 255–267 263 parent then recoil–aided and/or solution–caused mobilization has occurred. On the other hand, if the daughter–parent activity ratio is greater than unity it implies preferential leaching of the parent or preferential precipitation of the daughter radionuclides. The typical 234U/238U activity ratio is unity for the unweathered rocks and less than unity for weathered rocks. The key factors in the development of 234U/238U activity ratios out of equilibrium are the relative rates of leaching, mechanical erosion, and daughter half-life (Ivanovich & Harmon, 1992). The activity concentrations of 226Ra, 238U, 232Th and 40K, and the radiumequivalent activity in Bq/kg in Abu-Tartor phosphate and other phosphate deposits from different countries are given in Table 5. For the radium-equivalent activity, the minimum is for USSR (Kola) phosphate. For the phosphate deposits of sedimentary origin, Abu-Tartor phosphate has the minimum radium–equivalent activity value, 321 Bq/kg, followed by the phosphate ore from other Egyptian mines (Abu Zaabal phosphate plant) and Kurun phosphate from Sudan with 568 and 558 Bq/kg, respectively (Sam & Holm, 1995; Makweba & Holm, 1993; Olszewska, 1995; Hussein, 1994; Rossler et al., 1979; Guimond, 1990). The above results may indicate that the Egyptian phosphate rocks have the minimum radioactivity content for phosphate rock of sedimentary origin. The higher the radioactivity content in phosphate rocks, the higher are the radiological impacts and the radiation doses through mining, processing, phosphate product manfacturing and using phosphate products or by-products. Table 5 Activity concentration of 226Ra, 238U, 232Th, 40K and radium equivalent (Bq/kg) in phosphate rocks from different countries Country 226 238 Abu-Tartor, wet rocks Abu-Zaabal plant (Egypt) Morocco Tiba Togo (calcined) Bu-Croa (Western Sahara) USSR (Kola) USA (Florida)a USA (Western)a USA (North Florida) Matrix (ore) Rock concentrate Jordan Tunisia Algeria Israel Sudan (Uro) Sudan (Kurun) Tanzania (Arusha) 287 514 1600 1100 900 30 1600 1000 408 523 1700 1300 900 40 1500 1000 318 648 1044 821 619 1852 2263 555 5022 281 474 a 40 Ra U 2598 684 4641 232 Th 23.7 37 20 30 7 80 20 20 2 29 64 11 2.5 0.83 717 40 K Rad. eq. Ref. 21.4 19 10 4 30 40 323 568 1629 1143 912 147 1629 1029 This study Hussein (1994) Guimond (1990) Guimond (1990) Guimond (1990) Guimond (1990) Guimond (1990) Guimond (1990) 1048 865 712 1868 2270 558 6069 Rossler et al. (1979) Rossler et al. (1979) Olszewska (1995) Olszewska (1995) Olszewska (1995) Olszewska (1995) Sam and Holm (1995) Sam and Holm (1995) Makweba and Holm (1993) 8 32 22 51.7 23 286 K activity is not included in radium-equivalent activity calculation. 264 A.E.M. Khater et al. / J. Environ. Radioactivity 55 (2001) 255–267 The environmental pathways of natural radionuclides from phosphate rocks are given in Fig. 2. The untreated ground rock phosphate has been used in many parts of the world as plant fertilizer at a rate ranging from 300 to 600 kg/ha (104 m2) (Makweba & Holm, 1993). This is not the case in Egypt. Studies show that the additional external radiation exposure for the public, when using ground rock phosphate from Tanzania and Sudan, was negligible. Abu Tartor phosphate rock has a much lower radioactivity content than those ground rock phosphates (see Table 5). The calculated exposure rates (nGy/h) at 1 m above the ground due to natural radionuclides in wet phosphate rock and soil are given in Table 6. For soil, the exposure rate (35 nGy/h) is comparable to the Egyptian average (32 nGy/h) and less than the world average (55 nGy/h) (UNSCEAR, 1993). Data on the annual Fig. 2. Environmental pathways of natural radionuclides from phosphate rocks. Table 6 Calculated exposure rate (nGy/h) at 1 m above the ground due to natural radionuclides in wet phosphate rock and soil 226 232 40 0.461 132 11.8 (8.8–15.1)a } } 0.623 14.8 18.1(10.5–27.5) } } 0.041 0.89 5.34 (3.1–6.8) } } Ra nGy/h per Bq/kg Wet rock Soil Egypt World a Mean (range). Th K Total 148 35.3(22.3–49.4) 32 (8–93) 55 A.E.M. Khater et al. / J. Environ. Radioactivity 55 (2001) 255–267 265 effective dose to an average member of the public resulting from the extraction and processing of earth materials show that phosphate industries are dominating (Sam et al., 1999; Sam & Holm, 1995; Makweba & Holm, 1993; UNSCEAR, 1993). Considering the environmental behavior of radionuclides in soil, radium may be bound to the soil matrix to a relatively high extent over years because of its high affinity to clay minerals. In contrast, uranium is partially leached from the upper layers by water as uranyl ion (UNSCEAR, 1966). Also, the radionuclides deposited on the soil surface will usually be transported downwards by water infiltration and by ploughing, and the resulting soil layer above the source will provide greater shielding than the air above the ground alone (Sam et al., 1999). In the case of occupational exposure, it is reported that the annual effective dose to workers who handle phosphate rocks during industrial operation is 200 mSv/yr (UNSCEAR, 1993). It is well known that the most significant exposure pathways for those workers are the internal dose due to radon and dust inhalation during mining activities. This aspect should be studied in more detail to estimate the occupational radiation dose in Abu Tartor phosphate mine. A detailed dose assessment study will be carried out after the mine’s full operation. 4. Conclusions The radiological impacts of technologically enhanced natural radiation sources, especially phosphate mining and processing, are of great interest. The phosphate industries are dominating the radiation dose to an average member of the public received from geological material processing. From our results, it seems that Abu Tartor phosphate rocks have the lowest activity levels of exploited phosphate rocks of sedimentary origin and relatively the minimum radiological dose and environmental impacts through processing. Also, we can conclude that the radiation dose to a member of the public resulting from the use of Abu Tartor’s phosphate rocks and fertilizers is negligible compared to the average annual effective dose from natural sources (2.4 mSv/yr), even when assuming the complete accumulation of radionuclides in soil over many years. The processing rejects should be recycled to the greatest possible extent. For example, the slime (1.1 106 ton/yr) could be considered for land reclamation after estimating the maximum amount of slime to be added per area unit and their expected radiological impacts. Also, it is quite clear that there is no considerable radiological impact when using recycled water for irrigation of the future farm, as the radioactivity concentration of 226Ra and 232Th in this water is lower than the detection limit of the measuring technique used. Acknowledgements The authors wish to express their deep gratitude to Abu-Tartor Phosphate Project Authority for its technical support and sampling. The authors wish to acknowledge 266 A.E.M. Khater et al. / J. Environ. Radioactivity 55 (2001) 255–267 the support received from the Central Safety Department Forschungszentrum Karlsruhe gmbH and the International Bureau Julich in Germany. References Bahay, I., Youssef Hassan, M., & Abd El Nabi Attia Saad (1978). Geology of Abu Tartor plateau western desert-Egypt. Annals of the Geology Survey of Egypt, 8, 91–101. Bowen, H. J. M. (1979). Environmental chemistry of the elements. New York: Academic Press. El-Tahawy, M. S., Farouk, M. A., Hammad, F. H., & Ibrahiem, N. M. (1992). 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K., Mustafa, M. O. A., El Khangi, F. A., El Nigumi, Y. O., & Holm, E. (1999). Radiological and chemical assessment of Uro and Kurun rock phosphates. Environmental Radioactivity, 42, 65–75. Simon, S. L., & Ibrahim, S.A. (1990). Biological uptake of radium by terrestrial plant. Technical report No. 310, International Atomic Energy Agency (IAEA). Environmental behavior of radium. pp. (545–599). A.E.M. Khater et al. / J. Environ. Radioactivity 55 (2001) 255–267 267 UNSCEAR (1966). Ionizing radiation: sources and biological effects, United Nations Scientific Committee on the Effects of Atomic Radiation Report. UNSCEAR (1988). Ionizing radiation: Sources and biological effects. United Nations Scientific Committee on the Effects of Atomic Radiation Report. UNSCEAR (1993). Ionizing radiation: Sources and biological effects. United Nations Scientific Committee on the Effects of Atomic Radiation Report. United States Department of Energy, (USDOE). (1992). EML procedures manual. Environmental Measurement Laboratory Report No. HASL 300. ANALYSIS OF 238PU AND 239+240PU BY DESTRUCTIVE ASSAY TECHNIQUE FOR ENVIRONMENTAL SAFEGUARD PURPOSES Ashraf E. M. Khater*1, Yasser Y. Ebaid2, Sayed A. El-Mongy1 and Morsy S. El-Tahawy1 1 National Center for Nuclear Safety and Radiation Control, Atomic Energy Authority, P.O. Box 7551, Nasr City, Cairo 11762, Egypt. Tele/Fax: +202-274-0238. Email*: [email protected]. 2 Physics Department, Faculty of Science - Fayoum Branch, Cairo University - Fayoum Abstract Analysis of plutonium in environmental samples is one of the recent measures in order to strengthen the conventional international safeguards. Plutonium with some other actinides, and fission and activation products in environmental samples are currently used as indicators of undeclared nuclear activities. This work presents two destructive assay (DA) procedures for determination of and 239+240 238 PU PU in environmental samples. Alpha spectrometers were utilized to estimate the activity concentrations and to identify the isotopic composition of plutonium in the samples. U-test was applied to check the acceptance of the analysis results. The results of the analyzed reference and certified samples (soil, sediment and solution) show that the determined Pu concentrations are consistent with the target values. The concentration levels of 239+240 238 PU and PU in the analyzed samples ranged from 1.6 x 107 to 4.2 x 108 atoms, and from 2.2 x 1010 to 2.6 x 1011 atoms respectively. Both methods could be applied for accurate low-level analyses to estimate the plutonium isotopes concentration and their origin for environmental monitoring for safeguards purposes. Introduction In the framework of the modern approaches of the international community to strengthen the non-proliferation measures, analysis of environmental samples by destructive (DA) and non-destructive (NDA) techniques are expected to be a key tool for discovery of undeclared nuclear activities1,2 . It has to be mentioned that in most cases (except in accidental ones), environmental measurements will not produce a smoking gun. Rather, it will supply information that must be combined with other sources to determine what activities have taken place. Thus it is a supplement to conventional safeguards, not a replacement. Also monitoring of any release of man-made radioactivity to the environment is important for environmental protection. The problem of accurately detecting of extremely low level of Pu is gaining increased importance in application of nuclear counter-proliferation, verification, and environmental and waste management. The sources of Pu isotopes in the nature are the atmospheric nuclear weapons testing, the reentry burn up of a 238 Pu auxiliary powered navigational satellite (SNAP-9A), the nuclear fuel reprocessing plants, nuclear accident and the nuclear reactor effluents. Discrimination between different sources of anthropogenic Pu requires both precise and accurate isotopic ratio determination at environmental levels3. The earth crust and its surface contain only negligible quantities of natural Pu. In the environment, the mean specific activity of man-made 239Pu isotope is very close to 10 -13 g/g (0.23 mBq/g) for the surface soil. In some places, nuclear weapon testing sites, Pu producing nuclear reactor sites and close to the chemical factories of Pu extraction from nuclear fuel element, the specific activity of Pu can exceed the normal level by a factor greater than 10 2. The amounts of 238 Pu and 239+240 Pu, which have been released to the environment due to the above ground nuclear testing were about 1.2 × 107 and 3.3 × 105 GBq respectively4,5. Observation of any significant changes in the isotopic ratio of plutonium; 238 Pu/ 239+240 Pu, can probably indicate the presence of material from sources other than the global fallout. Whereas the activity ratio 238Pu/239+240Pu due to the fallout of weapons tests and the burning of the power supplies of satellites was 0.081, the ratios in the discharges of nuclear installations were up to 2.4 6. The 241 Pu/239+240Pu activity ratio varies very much depending on the origin of plutonium isotopes. For Fresh fallout from nuclear weapon tests, this activity ratio is about 12-16, while for spent nuclear fuel from power reactor it is about 130 5. The objective of this work is to study the convenience of the two destructive radiochemical procedures for plutonium isotopic analysis of different sample types for both traditional monitoring and environmental safeguards purposes. Description of the Procedures The monitoring of alpha emitting radionuclides such as 238 Pu and 239+240 Pu is complicated where thin and solid counting sources have to be prepared to minimize self absorption of alpha particles. For the preparaion of counting sources, the radioisotopes of interest have to be separated carrier-free from the sample material, applying suitable radiochemical separation procedures followed by electrodeposition. Two radiochemical analysis procedures for plutonium isotopes (238Pu and 239+240 Pu) analysis have been investigated as for their convenience. Flow charts of the two procedures are given in Figures 1 and 2. Determination of Pu in environmental samples by alpha spectrometry involves tedious radiochemical procedure to separate this radionuclide from the matrix. The first step in Pu isotopes separation from the matrix is the conversion of the Pu into acid soluble form. For Pu activity concentration and chemical yield determination, 236 Pu or 242 Pu was used as internal tracer. Both radiochemical procedures have been tested against standard and certified samples (soil, sediment and solution). Liquid-Liquid Extraction Method (LLE)4 Leaching/Dissolution: Plutonium-236 Tracer is added, for Chemical yield determination, to 100 grams aliquot of ashed samples. Samples are boiled for 30 minutes with 290 ml (8M HNO3)/(0.9M HF). Two and half grams of NaNO2 are added and the mixture is then filtered. The residue is boiled for 30 minutes with 250 ml (5M HNO3)/(1M Al(No3)3).Then 2.5 g NaNO2 is added and the mixture is filtered. The leached solution is adjusted to 500 ml with DI water. Separation and purification: Liquid-liquid extraction: The sample solution is transferred into a separatory funnel (1000 ml) and shaken for 15 minutes with 25 ml 0.2 M TOPO/cyclohexane. After phase separation, the TOPO/cyclohexane phase is transferred into another separatory funnel (250 ml). The aqueous phase is shaken once more for 15 minutes with 25 ml 0.2 M TOPO/cyclohexane. The organic phases are combined and washed three times with 50 ml 3 M HCl each. The washing solutions are discarded. Plutonium is back extracted in two steps to the aqueous phase using 25 ml of 0.5 M ascorbic acid/1M HCl each time. The organic phase is then discarded. The solution is washed three times, each time, for two minutes with 50 ml of CHCl3. Coprecipitation: The aqueous solution is transferred into 100 ml polyethylene centrifuge tube with 40 ml of HF (40%). Two ml of La(NO3)3 solution (10 mg/ml) are added. The fine crystalline precipitate is removed by 5-minute centrifugation at 3000 rpm. Two ml of La(NO3)3 solution (10 mg/ml) are added twice and centrifuged. After decanting, the solution is discarded. The precipitate is washed carefully with 15 ml 1.5 M HF and removed by 10-minute centrifugation at 3000 rpm. The precipitate is dissolved with 10 ml hot saturated boric acid and 10 ml HNO3 (68%). Then 0.25 ml 1.5 M NaNO2 solution is added. Ion exchange chromatography: The sample solution is passed through 8 ml column volume (c.v.) conditioned anion exchange column (Dowex 1x 2-50-100mesh, nitrate form). The conditioning is performed by washing the column with 8 c.v. of 7.2 M HNO3. After the sample solution has passed through the column, another washing is performed with 8 c.v. of 7.2 M HNO3 followed by 10 ml of 9 M HCl. In order to elute the plutonium, 10 ml of 0.36 M HCl/0.01 M HF is used. Eluate (containing Pu) is evaporated to dryness. One ml of conc. HCl is added and solution is taken to dryness two times. The residue is rinsed with 0.4 ml 4 M HCl and transferred to the electroplating cell. Electroplating: After the sample has been transferred to the electroplating cell, 3 ml of ammonium oxalate (4%) and 0.6 ml DI water are used to wash residues in the beaker and its wall and swirling the residue. The residue is then transferred to the electroplating cell. Plutonium is electroplated for three hours at 300 mA current. One minute before current disconnection, the electroplating process is quenched using 1 ml ammonium hydroxide solution (25%). Following the current disconnection, the solution is discarded and the cell is washed with DI water. The plated disk is washed with DI water and alcohol, and flamed using a Bunsen burner to be ready for counting. Ion exchange Chromatography Method (IEC): Dissolution: Ten grams aliquot of a dry soil sample is weighed into a 500 ml polyethylene Nalgene Bottle. Plutonium-242 tracer is added (100 to 150 mBq) to the sample. 200 ml of 48% hydrofluoric acid (HF) and 300 ml of concentrated nitric acid (HNO3) are added. A 1.0 inch teflon-coated stirring bar is placed in the bottle. The bottle is placed in a hot water bath on a magnetic stirring hot plate and the sample is stirred overnight while heated on medium temperature (100 0C). A second leach with HF or HF⋅and HNO3 may be needed if large quartz crystals are present. The mixture is then decanted into a 600 ml teflon beaker and let to evaporate to dryness. 200 ml of hydrochloric acid (HCl) and 5 g of H3BO3 are added to the dried sample and the sample is heated until 10 ml remains. Hundred ml of HNO3 is added to the sample and heated to remove the HCl. Cautiously hydrogen peroxide drops are added to oxidize any organic residues. The sample is evaporated until salts appear and left to cool down. The sample is then filtered through a Whatman GF/A Glass fiber filter using several washes of 7.2 M HNO3 until approximately 200ml is reached. Separation Anion exchange chromatography: One ml of 1 M NaNO2 solution is added per 100 ml sample solution, mixed thoroughly and then allowed to stand at room temperature for approximately 1 hour. A slurry of anion exchange resin (AG-1X4, 50-100 mesh, chloride form, Bio-Rad) is prepared using distilled water. A small glass wool plug is tightly packed into the tip of the ion-exchange tube. The resin slurry is transferred into the ion-exchange tube. Bubbles are avoided when packing the resin. The resin bed is washed with three 20 ml aliquots of 7.2 M HNO3. All resin should be carefully washed from the column reservoir and walls. A glass wool plug is gently placed on the top of the column containing the resin while part of the third 20 ml aliquot of 7.2 M HNO3 remains in the reservoir. The sample solution is poured through the resin column, keeping the reservoir filled with approximately 40 ml of sample solution. Two 20 ml portions of 7.2 M HNO3 are added to the column. The column is then washed with two 25 ml of 8 M HCl. The plutonium is eluted from the column with four 20-ml aliquots of freshly prepared solution containing 1g/l of NH4I in 1M HCl7,8,9. Electroplating In order to drive off the iodine, 1 ml of conc. HNO3 is added to the plutonium elute solution and evaporated to dryness. A mixture of 1 ml of conc. HNO3 and 5 ml of conc. HCl is added to the residue and evaporated to dryness “until just dry”. Another 5 ml of conc. HCl is added to the residue and is evaporated until the first dry spots appear. The wall of the beaker is washed down with 5 ml of conc. HCl and then the sample is evaporated until almost 0.5 ml is left. About 3 ml of 4% ammonium oxalate solution is added and the mixture is transferred to the electrodeposition cell. One Ampere current is applied for 30 min and the reaction finally quenched with 1 % NH4OH. The plated disk is washed with DI water and alcohol, and flamed using a Bunsen burner to be ready for counting. For determination of plutonium isotopes activity concentration and their ratio, the electroplated disks were measured using alpha spectrometers based on passivated implanted planar silicon (PIPS) detectors with 450 mm2 surface area and about 25 % efficiency and about 20 keV resolution at 4.41 MeV of 241Am was used. The detector was calibrated using a standard mixed source containing 239 Pu, 241Am and 244 Cm. The samples were measured for 60000 - 80000 second. Results and Discussion The results of 238 Pu and 239+240Pu obtained by LLE and IEC procedures are given in tables 1 and 2, respectively. The concentration levels of 238 PU and 239+240PU in the analyzed samples ranged from 1.56.107 to 4.24.108 atoms (from 3.92 to 106.0 mBq/g), and from 2.2.1010 to 2.6.1011 atoms (from 20.3 to 236.0 mBq/g), respectively. Typical spectra of the measured plutonium are shown in Figure 3. The results were evaluated against the follwing acceptance criteria for accuracy and precision. A result must pass both criteria to be assigned the final status of “passed”10. Accuracy: result passes if, 2 2 ValueCert . − ValueMeas. ≤ 3.29 × Unc.Cert . + Unc. Meas . Where: 3.29 is the U-Test value, which indicates that the reported result is not significantly differs from certified value. Precision: the result passes if, 2 2 UncCert . Unc Meas. × 100 ≤ 15 ⇒ 40% * + ValueCert . Value Meas. * Dependant on the activity concentration (15 % for high activity and 40% for low activity). Regarding the samples preparation, (double leaching with HNO3/HF and HNO3/Al(NO3)3 , and total sample dissolution), the results showed that both of them have succeeded to bring the refractory compounds of plutonium in the analyzed samples into an acid soluble form11. Table 1. Quality control data for reference and certified samples analyzed using LLE procedure and alpha spectrometry for plutonium isotopes. 238 239+240 Pu Pu Comments Sample code Certified (mBq.g-1) Measured (mBq.g-1) U-test value Certified (mBq.g-1) Measured (mBq.g-1) U-test Value IAEA-384 39.0± 1.1 35.4 ± 2.3 2.5 108 ± 2.5 100.5 ± 6.3 1.11 Sediment 8 14 (1.41.10 atom) 35.9 ±0.7 Spiked Soil* 34.0± 3.0 (1.1.10 atom) 0.61 77.0± 1.6 68.0± 5.0 8 114.0 ±2.3 Solution 106.0 ± 9.0 244.0+4.9 236.0+18.0 - 0.41 Passed 0.02 Passed 11 (2.6.10 atom) (4.24.10 atom) - Passed (7.4.10 atom) 0.86 8 Standard 1.66 10 (1.36.10 atom) Standard Acceptance criteria Passed - 191.0+3.8 190.0+4.3 11 (2.1.10 atom) Solution * mBq/Sample 1 mBq 239 9 Pu = 1.09x10 atom, 1 mBq 238 Pu = 3.99x106 atom. Table 2. Quality control data for certified soil samples analyzed using IEC procedure and alpha spectrometry for plutonium isotopes. 238 239+240 Pu Sample code Ref. Soil (1) Pu Certified (mBq.g-1) Measured (mBq.g-1) U-test 3.81 ± 0.15. 3.92 ± 0.31 0.3 value Certified (mBq.g-1) Measured (mBq.g-1) U-test 25.90 ± 0.74 25.70 ± 1.33 0.1 (1.56.107 atom) Ref. Soil (2) 11.47 ± 0.37 12.16 ± 0.56 20.72 ± 0.70 18.5 ± 0.78 (7.38.107 atom) Value Acceptance criteria Passed (2.8.1010 atom) 1.0 22.20 ± 0.74 (4.85.107 atom) Ref. Soil (3) Comments 23.03 ± 0.96 0.5 Passed (2.5.1010 atom) 2.1 20.35 ± 0.63 20.32 ± 0.84 0.03 Passed (2.2.1010 atom) In regards to the time needed for analysis, namely a batch of four samples, the LLE procedure showed a shorter time for analysis. However, for larger batches (up-to-18 samples) the IEC procedure showed better performance. The LLE procedure results in a mixed organic radioactive waste while the IEC procedure produces only an aqueous radioactive waste, which is easier in handling from the waste management point of view. The lower limits of detection obtained by the LLE and IEC procedures are 1.0 and 0.74 mBq/sample (3.99 x 106 and 2.9 x 106 atoms for 238 Pu, and 1.09x 109 and 8.1x 108 atoms for 239 Pu) respectively. Lower Limits of detection, as low as 2.9 x 103 atoms for 238Pu, could be reached depending on the procedure parameters such as sample size and counting time. CONCLUSIONS It was observed that the analysis of plutonium and its isotopic composition in environmental samples by the presented destructive assay procedures is effective and fulfill the requirements of environmental monitoring and the recent approaches of the international safeguards. As low as 3.99 x 106 and 2.9 x 106 atoms/sample of 238Pu and 1.09x 109 and 8.1x 108 of 239 Pu atoms/sample for LLE and IEC procedures respectively could be obtained. The presented procedures could also be used for swipe sample analysis. Development of the procedure to reach lower detection limit of Pu is an on-going activity. References 1. G. Andrew. Prospects for Environmental Monitoring in International Safeguards, Proceedings of the International nuclear Safeguards Symposium,1994, Vol. 1 International Atomic Energy Agency. 2. International Atomic Energy Agency, The Additional Protocol to the NPT (INFCIRC/540), 1997, IAEA, Vienna, Austria. 3. P. Linsalata, M.E. Wrenn, N. Cohen and N. P. Singh. American Chemical Society, 1980, 14 (2), 1519-1523. 4. M. Pimpl and H. Scuettelkopf. The measurement of Pu in Environmental samples and in Gaseous and liquid effluents of nuclear installations. Swedish University of Agricultural Sciences, Uppsala, 1986, Report SLU-REC-61, 5362. 5. M Hakanen, T. Jaakola and H. Korpela. Nucl. Instrum. Methods Phys. Res., 1984, 223, 382-383. 6. Z. Holgye, F. Filgas and V. J. peskova. Radioanal. Nucl. Chem. Lett., 1989, 17, 135. 7. Strezov, A., Yordanova, I., Pimpl, M. and Stoilova, Health Physics, 1996, 70 (1), 70-80. 8. Peters, R. J., Knab, D., Eberhardt, W. Plutonium in Soil and Water SamplesAlpha Spectrometry” Method No. ER160,1984, Health and Environmental Chemistry Analytical Techniques, Data Management, and Quality Assurance, LA-10300-M, Vol. II Manual, Los Alamos National Laboratory. 9. Y. Y. Ebaid, M. S. El-Tahawy, A. A. El-Lakkani, S. R. Garcia and G. H. Brooks J. adioanalytical and Nuclear Chemistry, 2000, 243, 2. 10. Brookes, C.J. Bettekey, I. G., and Loxton, S. M., 1979 “Fundamentals of Mathematics and Statistics” Wiley, New York. 11. UNSCEAR: United Nations Scientific Committee on the Effect of Atomic Radiation, 1982, Report to the General Assembly. Ashed sample material add yield tracer Pu-236 leaching with 8 M HNO3 / 0.9 M HF leaching with 5 M HNO3/ 1 M Al(NO3)3 add NaNO2, filtrate Dissolved Sample Material Extraction with TOPO/ Cyclohexane Aqueous Phase: discard Organic Phase: wash 3 times with 3 M HCl Back-extraction with 0.5 M Ascorbic Acid/1 M HCl Organic Phase: discard Aqueous Phase: wash 3 times with CHCl3 Coprecipitation with LaF3 wash precipitation with 1.5 M HF dissolve H3BO3 (saturated)/HNO3 (65%) add NaNO2 Anion-Exchange Dowex 1x2, 50 - 100 mesh wash with 7.2 M HNO3 wash with 9 M HCl eluate with 0.36 M Hcl/0.01 M HF evaporate to dryness dissolve with 4 M HCl add (NH4)2C2O4 (4%) Electro-deposition Alpha-Spectrometry 12. Fig. (1): Flow chart illustrating the basic elements of the radiochemical procedure for plutonium analysis (LLE). Ashed sample material add yield tracer Pu-242 Totally dissolved with HNO3, HF, HCl and H3BO3 Dissolved Sample Material Anion-Exchange Dowex 1x2, 50 -100 mesh wash with 7.2 M HNO3 wash with 9 M HCl eluate with NH4I/1M HCl evaporate to dryness dissolve with 0.1 M HCl add (NH4)2C2O4 (4%) 1 Amp current applied for 30 min Electro-deposition Alpha-Spectrometry Fig. (2): Flow chart illustrating the basic elements of the radiochemical procedure for plutonium analysis (IEC) . (a) LLE procsdure. 100 239+240 236 Pu Pu 80 Counts 60 238 Pu 40 20 0 271 281 291 301 311 321 331 341 Channal number (b) IEC procedure 350 239+240 300 Pu counts 250 242 200 Pu 150 100 238 50 Pu 0 30 40 50 60 70 80 90 100 channel number Figure 3: Typical Alpha Spectra of Plutonium Isotopes. 110 Journal of Environmental Radioactivity 73 (2004) 151–168 www.elsevier.com/locate/jenvrad Environmental characterization and radio-ecological impacts of non-nuclear industries on the Red Sea coast M.H. El Mamoney a, Ashraf E.M. Khater b, a b National Institute of Oceanography & Fisheries, Alexandria, Egypt National Centre for Nuclear Safety and Radiation Control, Atomic Energy Authority, PO Box 7551, Nasr City, Cairo 11762, Egypt Received 1 January 2003; received in revised form 1 July 2003; accepted 23 August 2003 Abstract The Red Sea is a deep semi-enclosed and narrow basin connected to the Indian Ocean by a narrow sill in the south and to the Suez Canal in the north. Oil industries in the Gulf of Suez, phosphate ore mining activities in Safaga—Quseir region and intensified navigation activities are non-nuclear pollution sources that could have serious radiological impacts on the marine environment and the coastal ecosystems of the Red Sea. It is essential to establish the radiological base-line data, which does not exist yet, and to investigate the present radio-ecological impact of the non-nuclear industries to preserve and protect the coastal environment of the Red Sea. Some natural and man-made radionuclides have been measured in shore sediment samples collected from the Egyptian coast of the Red Sea. The specific activities of 226Ra and 210Pb (238U) series, 232Th series, 40K and 137Cs (Bq/kg dry weight) were measured using gamma ray spectrometers based on hyper-pure germanium detectors. The specific activities of 210Po (210Pb) and uranium isotopes (238U, 235U and 234U) (Bq/kg dry weight) were measured using alpha spectrometers based on surface barrier (PIPS) detectors after radiochemical separation. The absorbed radiation dose rates in air (nGy/h) due to natural radionuclides in shore sediment and radium equivalent activity index (Bq/kg) were calculated. The specific activity ratios of 228Ra/226Ra, 210Pb/226Ra, 226 Ra/238U and 234U/238U were calculated for evaluation of the geo-chemical behaviour of these radionuclides. The average specific activity of 226Ra (238U) series, 232Th series, 40K and 210 Pb were 24.7, 31.4, 427.5 and 25.6 Bq/kg, respectively. The concentration of 137Cs in the sediment samples was less than the lower limit of detection. The Red Sea coast is an arid Corresponding author. Present address: King Saud University, College of Science, Physics Dept., P.O. Box 2455, Riyadh 11451, Kingdom of Saudi Arabia. Tel.: +996 52 41 8292; fax: +996 14 67 3656. E-mail address: [email protected] (A.E.M. Khater). 0265-931X/$ - see front matter # 2003 Published by Elsevier Ltd. doi:10.1016/j.jenvrad.2003.08.008 152 M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 region with very low rainfall and the sediment is mainly composed of sand. The specific activity of 238U, 235U and 234U were 25.3, 2.9 and 25.0 Bq/kg. The average specific activity ratios of 226Ra/228Ra, 210Pb/226Ra and 234U/238U were 1.67, 1.22 and 1.0, respectively. The relationship between 226Ra/228Ra activity ratio and sample locations along the coastal shoreline indicates the increase of this ratio in the direction of the Shuqeir in the north and Safaga in the south where the oil exploration and phosphate mining activities are located. These activities may contribute a high flux of 226Ra. The concentration and distribution pattern of 226Ra in sediment can be used to trace the radiological impact of the nonnuclear industries on the Red Sea coast. # 2003 Published by Elsevier Ltd. Keywords: Natural radioactivity; Red Sea; Coastal environment; Non-nuclear industries 1. Introduction Radionuclides have been an essential constituent of the earth since its creation. The earth’s is still being heated through the decay of long-lived natural radionuclides e.g. uranium, thorium and potassium. All uses of natural or man-made radionuclides require an understanding of their environmental behaviour. Such knowledge is needed for their effective application as in-situ tracers or geo-chronometers and for estimation of human health risks. The advent of nuclear science resulted in the proliferation of nuclear applications and in the increase of environmental radioactivity levels. Further, we are exposed to radionuclides brought to the surface by man’s traditional working activities such as mining operations and oil explorations, which have contributed to the increase of population radiation dose due to environmental radioactivity. Egypt has about 700 km of coastline along the Red Sea proper, which is of great environmental, economical and recreational value. Commercial and subsistence fisheries provide a living for a large sector of the coastal population in Egypt. The eco-tourism infrastructure is continuously developing along the Egyptian Red Sea coast. The Red Sea—Suez Canal pathway is one of the most important international marine pathways with highly intensive ship traffic. Some of these ships are running by nuclear power or carrying radioactive materials, which is a source of possible accidental contamination (Hawkins and Roberts, 1993). In the Gulf of Suez, the northern part of the Red Sea, there are about 90% of the Egyptian oil exploration and production activities, which could be a significant source of environmental contamination with technological enhanced naturally occurring radioactive materials (TENORM). On the Red Sea coast, there are two main centers for phosphate ore mining: Safaga and Quseir and three shipping harbours. Mining of the Red Sea coastal phosphorites began in 1910, for export to the Far East. The phosphatic deposits in the Quseir–Safaga district of the Red Sea coast are mined at many localities in the Quseir group of mines (Hamadat, Atshan, Duwi, Anz, Abu Tundub, Hamrawein), and at Safaga group of mines (Um El-Howeitat, Gasus, Wasif, Mohamed Rabah). M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 153 Phosphate ore dust spilled over into the Sea during shipping is considered as a continuous source for contaminating the Red Sea coastal environment (IOC, 1997 and Said, 1990). There is a lack of information about the radioactivity levels and characterisation of the Egyptian Red Sea coastal environment. This information is essential to create a scientific database of the radiological base-line levels and to identify the radiological impacts of non-nuclear industries (e.g. phosphate mining, phosphate shipping and oil production activities) or any accidental contamination on the coastal region of the Red Sea. The study on the concentrations of heavy metal pollution in the Egyptian Red Sea, over 50 years period (1934–1984), has shown that the concentrations of most of the heavy metals has increased, due to natural pollution from hot brine pools or due to man-made pollution from oil, heavy metal mining, discharge of domestic industrial wastes and phosphate mining and transportation along the Red Sea coastal areas (Hanna, 1992). Our study is the first to focus on the spatial distribution pattern and levels of radioactivity in the Egyptian Red Sea coastal environment. These results will be useful to evaluate the present radio-ecological impacts of the non-nuclear industries (e.g. oil production and phosphate mining) on the coastal environment. Also, these data will be available for subsequent evaluations of the possible future environmental contamination due to the non-nuclear industries. 2. Material and methods 2.1. The study area The Red Sea occupies an elongated escarpment-bounded depression, which extends in a south-east direction from Suez to the strait of Bab El-Mandeb in a nearly straight line. It separates the coasts of Arabia from those of Egypt, the Sudan and Ethiopia. Its total length is about 2200 km, and its breadth varies from 400 km in the southern half to 210 km in the north where it bifurcates into two arms, the Gulf of Suez and the Gulf of Aqaba (Said, 1990). The Red Sea is connected with the Mediterranean Sea by the Suez Canal, which has no locks; however, this connection is of no practical importance for exchange of water. In the south, the strait of Bab El-Mandeb limits water exchange between the Red Sea and the Gulf of Aden. The rainfall over the Red Sea and its coasts is extremely low. Evaporation exceeds precipitation, and this combined with the very restricted exchange of water with the open sea lead to the production of the dense, highly saline water (Khatir et al., 1998a,b). The narrow coastal plain of the Egyptian Red Sea lies between the high fringing mountains consisting mostly of crystalline rocks and the seawater. Along the shores, there is an almost continuous band of emergent reef terraces between 0.5 and 10 km wide. Between these and the foot of the crystalline hills extends a sand gravel surface. The width of this plain ranges from less than 1 to 20 km. The main sources of sediments to the beaches of the Egyptian Red Sea are terrestrial deposits 154 M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 transported from the fringing mountains during the occasional runoffs through the numerous wadis, and the Middle Miocene and later biogenic carbonate sediments (El Mamony and Rifaat, 2001). 2.2. Sampling and samples preparation The samples were collected from the beach face along the entire area of study, v which extended from Shuqeir north (latitude 28 30 3900 N) to Marsa Alam city v south (Latitude 25 40 2900 N). Forty shore sediment samples were collected in 1997. The beach sediments in the study area are predominantly sand. The content of terrestrial deposit is the major control in determining the mean grain size of the sediment where most of the coarse sands are mainly quartz, feldspar and other silicate mineral grains. The samples were collected using a template of 25 25 cm2 area and 5 cm depth (USDOE, 1992). The gravels size greater than 2 cm were discarded. The sampling locations are shown in Fig. 1. The geographical description of sampling locations: samples density (kg/l), mean grain size, and sorting; CO3%, Ba (ppm) and Sr (ppm) in the collected samples are given in Table 1 (El Mamony v and Rifaat, 2001). The collected samples were dried at 110 C, pulverised, homogenised and sieved through a 2 mm mesh. For uranium isotopes analysis portions Fig. 1. Map of Egypt and the studied area of the Red Sea Egyptian coast. CODE 453 455 456 458 459 461 462 463 464 468 469 470 471 473 474 475 476 501 505 507 508 509 510 511 512 515 518 522 524 Ser. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 Shuqeir South Shuqeir South Shuqeir South Ras El’Esh Gebel El’Zeit Gebel El’Zeit Gebel El’Zeit Ras El’Esh Ras Jemsha 50 km North Hurghada 40 km North Hurghada 35 km North Hurghada – 27 km North Hurghada – 20 km North Hurghada 15 km North Hurghada 12 km North Hurghada Sharm El’Arab Sharm El’Naga Ras Abu Suma Abu Suma Bay 7 km North Safaga Safaga City 5 km South Safaga 20 km South Safaga 40 km North Quseir 20 km North Quseir 10 km North Quseir Location 28 03 39 28 00 48 27 58 09 27 52 07 27 49 51 27 47 55 27 45 00 27 44 01 27 41 01 27 37 05 27 34 05 27 31 34 – 27 26 36 27 15 34 27 21 38 27 17 34 27 07 14 26 58 00 26 53 57 26 50 51 26 50 11 26 47 10 26 43 18 26 40 39 26 33 59 26 25 42 26 15 10 26 09 55 N (Deg. Min. s) 33 20 09 33 26 23 33 29 52 33 33 44 33 34 51 33 29 22 33 31 38 33 32 54 33 33 22 33 32 11 33 33 57 33 33 44 – 33 39 14 33 48 43 33 41 07 33 45 43 33 49 44 33 55 17 33 57 48 33 59 17 33 56 58 33 56 15 33 56 14 33 56 03 34 02 06 34 06 09 34 12 07 34 14 37 E (Deg. Min. s) 1.42 1.56 1.70 1.50 1.80 1.52 1.69 1.53 1.60 1.68 1.63 1.60 1.53 1.54 1.48 1.64 1.84 1.8 1.76 1.61 1.76 1.68 1.70 1.70 1.72 1.50 1.50 1.60 1.35 Density (g/ml) Very coarse sand Medium sand Very coarse sand Very coarse sand Coarse sand Very coarse sand Medium sand Medium sand Medium sand Medium sand Medium sand Medium sand – Medium sand – Medium sand Fine sand Medium sand Medium sand Medium sand Medium sand Fine sand Coarse sand Medium sand Medium sand Medium sand Medium sand Fine sand Medium sand Mean grain size Moderately well sorted Moderately well sorted Very well sorted – Moderately sorted Moderately well sorted Moderately well sorted Moderately sorted Very well sorted Poorly sorted Moderately sorted Moderately well sorted – Moderately sorted – Moderately sorted Moderately well sorted Moderately sorted Moderately sorted Moderately well sorted Moderately well sorted Moderately sorted Moderately sorted Poorly sorted Moderately well sorted Moderately well sorted Poorly sorted Well sorted Poorly sorted Sorting Ba (ppm) Sr (ppm) 40.8 2093 4037 57.7 2757 6755 16.9 778 1232 13.2 227 1078 38.5 1551 3987 28.0 2084 1561 8.7 3170 483 55.0 1538 7176 3.5 184 108 34.1 1690 4495 23.0 1834 3741 6.5 393 484 – – – 22.4 951 2668 – – – 20.2 1192 2729 13.7 1706 1207 20.7 2273 1931 16.0 3021 2114 9.5 3162 894 21.5 2693 3229 19.6 2336 3983 2.9 ND ND 27.6 2813 3128 22.6 1896 3701 43.8 2247 4647 56.6 3394 6338 25.7 3217 3996 79.6 5450 8073 (continued on next page) CO3 (%) Table 1 Geographic description of sampling locations; samples density (g/ml), mean grain size (phi), and sorting; CO3 (%), Ba (ppm) and Sr (ppm) in shore sediment samples of the Red Sea coast (El Mamony and Rifaat, 2001) M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 155 CODE 528 530 531 534 536 538 541 545 548 549 551 30 31 32 33 34 35 36 37 38 39 40 14 km South Quseir 25 km South Quseir 36 km South Quseir 45 km South Quseir 55 km South Quseir Umm Qirayfat (67 km South Quseir) 82 km South Quseir 28 km North Marsa Alam 14 km North Marsa Alam 9 km NorthMarsa Alam (Wadi Aslai) Marsa Alam City Location Table 1 (continued ) Ser. 25 04 29 25 09 26 25 11 42 25 28 45 25 18 51 26 00 21 255 25 53 16 25 46 04 25 41 15 25 36 31 N (Deg. Min. s) 34 53 52 34 51 06 34 49 20 34 40 36 34 45 01 34 20 03 34 23 42 34 24 43 34 30 53 34 33 50 34 36 17 E (Deg. Min. s) 1.72 1.62 1.54 1.80 1.50 1.62 1.66 1.74 1.30 1.58 1.56 Density (g/ml) Medium sand Medium sand Fine sand Fine sand Fine sand Coarse sand Medium sand Medium sand Medium sand Fine sand Coarse sand Mean grain size 92.0 57.7 59.3 70.9 32.9 63.4 CO3 (%) Moderately well sorted 22.8 Moderately well sorted 48.9 Moderately well sorted 42.8 Moderately well sorted 38.5 Moderately well sorted 11.5 Moderately sorted Moderately well sorted Poorly sorted Moderately well sorted Moderately sorted Well sorted Sorting 2087 1826 5394 1479 1431 3766 4923 3898 4863 966 3162 Ba (ppm) 1153 5536 5209 5418 740 6467 8034 4787 5920 3353 5651 Sr (ppm) 156 M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 157 of the dried samples were moistured with concentrated nitric acid, fumed off to v dryness, and ashed at 550 C for about 12 h (Khater, 1997). 2.3. Analytical techniques 2.3.1. Gamma spectrometric analysis The dried samples were transferred to polyethylene containers of 100 cm3 capacity and sealed at least for 4 weeks to reach secular equilibrium between radium and thorium, and their progenies. 226Ra (238U) series, 232Th series, 40K, 137 Cs and 210Pb specific activities were measured using well-calibrated gamma spectrometry based on hyper-pure germanium (HpGe) detectors. The HpGe detector had a relative efficiency of 40% and full width at half maximum (FWHM) of 1.95 keV for 60Co gamma energy line at 1332 keV. The gamma transmissions used for activity calculations are 352.9 (214Pb), 609.3, 1120.3 and 1764.5 keV (214Bi) for 226 Ra (238U) series, 338.4, 911.1 and 968.9 keV (228Ac) for 232Th series, 1460.7 keV for 40K, 661.6 keV for 137Cs and 46.5 keV for 210Pb. The gamma spectrometers were calibrated using both 226Ra point source and potassium chloride standard solutions in the same geometry as the samples (Khater, 1997). The lower limits of detection, with 95% confidence, for 226Ra, 232Th and 40K are 0.28, 0.16 and 1.0 Bq/kg, respectively for 20 h counting time and 1 l sample volume (Currie, 1968). 2.3.2. Uranium isotopes analysis Ashed samples (2–5 g) were spiked, for chemical recovery and activity calculations, with about 70 mBq 232U tracer and dissolved using mineral acids (HNO3, HF and HCl). Uranium was extracted with trioctylphosphine oxide in cyclohexane, back-extracted with NH4F/HCl solution, then co-precipitated with La(NO3)3 and purified by passing through an anion exchange column. Uranium was electroplated on a stainless-steel disk from oxalate–chloride solution. The prepared samples were measured using alpha spectrometry (CANBERRA 4701 vacuum chambers) based on surface barrier (PIPS) detectors with 450 mm2 surface area, about 25% efficiency and about 20 keV resolution, and connected up to a computerised multichannel analyser operating with Genie 2000 software (CANBERRA). The lower detection limit of the procedure is about 1 mBq/sample (1000 min measuring time) (Pimpl et al., 1992). The chemical recovery was in the range of 40–70%. 2.3.3. Lead-210–Polonium-210 analysis Dried samples (1–2 g) were spiked, for chemical recovery and activity calculation, with about 80 mBq 208Po and dissolved using mineral acids (HNO3, HF and HCl). Finally, the samples residuals were dissolved in 30 ml of 0.5 M HCl. About 100 mg of ascorbic acid was added to the hot solution to reduce the iron content. Then, polonium was self-plated from the solution at temperatures between v 80 and 90 C onto rotating stainless steel disk fixed in a Teflon disk holder (Hamilton and Smith, 1986). The plated disks were measured using alpha spectrometers described above. The samples were measured for 1000 min, applying a lower limit of detection of 1 mBq (Currie, 1968). The average chemical recovery was 75%, and 158 M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 the individual values ranged from 50 to 100%. The measured is equivalent to 210Pb specific activity. 210 Po specific activity 2.4. Theoretical calculations Radium equivalent activity (Bq/kg) is an index which is convenient to compare the specific activities of samples containing different concentrations of 226Ra, 232Th and 40K. It is defined based on the assumption that 10 Bq 226Ra/kg, 7 Bq 232Th/kg and 130 Bq 40K/kg produce the same gamma dose rate. It is calculated using the following equation: 10 10 Raeq ¼ CRa þ CTh þ CK 7 130 Where CRa, CTh and CK are activity concentrations (Bq/kg dry weight) of 226 Ra, 232Th and 40K, respectively (Khater, 1997). Absorbed dose in air (nGy/h) 1 m above the ground surface due to natural radionuclides (226Ra series, 232Th series and 40K) in shore sediment was calculated using the following equation (UNSCEAR, 2000): D ðnGy=hÞ ¼ 0:462CRa þ 0:604CTh þ 0:042CK Where CRa, CTh and CK are the specific activities (Bq/kg dry weight) of 232 Th and 40K, respectively. 226 Ra, 3. Results and discussion Activity concentrations of 226Ra (238U) series, 232Th series, 40K, and 210Pb (Bq/ kg dry weight) in the shore sediment samples are shown in Table 2. The average ac tivity standard error (range) of 226Ra (238U) series, 232Th series, 40K, 210Pb (gamma) and 210Pb(alpha) were 24:7 4:3 (5.3–105.6), 31:4 9:41 (2.34–221.9), 42 7:5 35:5 (97.58–1011.3), 25:6 3:9 (7.1–81.8) and 23:9 3:7 (8.1–96.0) Bq/kg dry weight, respectively. The range of measured activities differed widely as their presence in marine environment depends on their physical, chemical and geo-chemical properties and the pertinent environment (Khatir et al., 1998a,b). In coastal waters, it can be assumed that the mineral fraction of the sediment has uranium and thorium contents similar to those of terrestrial rocks (Strezov et al., 1996). The average activities (range) of 226Ra (238U) series, 232Th series and 40K in Egyptian soil are 17 (5–64), 18 (2–96) and 320 (29–650) Bq/kg dry weight, respectively (UNSCEAR, 2000). The activity of caesium-137 in the shore sediment samples was less than the lower limit of detection (0.1 Bq/kg, for 12 h measuring time) (Currie, 1968). This could be because the coastal region of the Red Sea is free from any direct anthropogenic radioactive waste discharge; it has an arid region with extremely low rainfall, and is composed mainly of sand, which has low adsorption capacity. The average activity of 137Cs in bottom sediment of Sudanese Red Sea coast is 4.1 Bq/kg (Khatir et al., 1998a,b). It is less than the values from the pre-Chernobyl M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 159 Table 2 Specific activity (Bq/kg dry weight) of Ra-226 series, Th-232 series, K-40 and Pb-210 in shore sediment samples of Red Sea coast Ser. Code Ra-226 E Th-232 E K-40 E Pb-210a E Pb-210b Ec 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 453 455 456 458 459 461 462 463 464 468 469 470 471 473 474 475 476 501 505 507 508 509 510 511 515 518 522 524 528 530 531 534 536 538 541 545 548 549 551 8:95 1:27 6:05 1:29 18:14 0:89 31:59 3:22 11:91 0:90 12:29 1:14 9:67 1:08 5:53 0:32 8:51 0:85 9:08 0:90 20:30 1:44 9:60 2:21 9:97 1:47 11:16 1:01 – 50:25 1:25 87:32 2:19 105:56 2:99 37:87 1:53 96:22 2:25 14:19 1:16 – 22:08 2:12 67:75 2:44 11:13 1:05 14:67 2:47 18:70 1:46 6:5 1:1 16:28 0:99 33:07 1:05 44:38 1:98 8:26 0:76 17:66 1:39 5:32 0:92 27:22 4:28 9:99 1:34 10:39 1:66 9:62 1:0 – 3:32 1:55 4:27 0:70 13:95 1:09 18:49 2:91 5:69 1:11 10:95 1:29 6:37 1:75 5:59 0:45 4:56 0:76 7:62 0:88 15:63 1:24 8:10 2:64 6:57 1:32 9:28 1:02 – 132:46 1:81 221:90 3:52 205:17 4:15 66:31 2:52 143:61 2:89 15:01 1:16 – 18:67 2:47 12:72 2:79 2:34 0:88 8:90 2:92 4:00 0:87 <DL 4:53 1:03 33:86 1:47 37:08 2:15 4:59 2:27 9:69 1:43 3:34 1:31 32:69 4:06 9:70 1:90 5:48 2:42 6:92 2:03 – 425:17 13:05 97:58 6:96 634:33 6:09 1011:30 27:73 377:02 6:64 620:96 11:23 616:30 10:68 370:87 5:30 401:00 0:76 435:63 7:93 457:15 9:23 376:16 15:37 524:89 13:91 394:84 7:62 – 587:70 7:17 377:02 8:93 572:92 13:81 725:10 12:04 725:16 27:40 635:75 8:90 – 886:50 14:20 485:30 12:15 310:48 8:01 282:08 12:69 253:66 9:58 128:14 7:53 224:55 6:36 136:27 5:85 313:54 10:54 194:48 6:32 434:68 10:56 294:70 9:87 118:28 7:10 257:26 8:36 444:60 17:23 257:81 6:99 – – 7:90 0:79 13:95 1:37 22:05 3:58 9:88 1:02 19:50 1:94 <LLD 9:44 0:78 – – 11:08 0:98 13:54 1:42 7:08 0:90 14:07 1:22 – 29:34 3:40 77:30 7:73 48:85 11:67 50:51 5:56 80:99 3:13 19:76 2:17 – 10:46 1:10 81:75 5:09 23:71 2:61 <LD 29:63 2:04 8:72 1:05 25:61 2:59 28:56 2:23 – 16:93 1:76 14:82 1:84 11:40 1:39 29:63 3:26 23:71 3:01 11:85 1:19 14:63 1:46 – 10:24 0:64 8:07 0:70 18:78 1:18 17:54 1:34 15:71 0:79 16:09 1:32 10:98 0:94 13:86 1:09 – 11:95 0:99 17:97 1:31 14:49 1:20 12:38 1:27 14:83 1:19 10:30 0:91 73:35 3:40 – – – 96:01 5:71 25:42 2:89 22:93 1:43 – 81:41 4:32 13:39 1:49 8:67 0:92 32:68 1:68 12:29 1:35 31:61 4:71 – 23:41 1:54 22:04 1:91 23:26 1:12 23:31 2:36 34:75 2:61 17:00 1:64 – 14:51 0:87 14:61 1:37 a b c Pb-210 Gamma analysis. Pb-210 alpha analysis. Error (statistical and counting error only). period cited in the literature for marine sediments from different regions of the world (Khater, 1997; Khatir et al., 1998a,b; El Mamony and Rifaat, 2001). Relationships between 226Ra and 232Th, 40K, 210Pb, and Ba concentrations in the Red Sea shore sediment samples are given in Fig. 2. The relationships between 160 M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 226 Ra and 232Th, and 210Pb were strongly correlated with correlation coefficients (R) values of 0.89 and 0.91, respectively. These strong correlations could be because Ra and Th have some similarity in their environmental origin, i.e. the rocks from which the shore sediment were formed, and their chemical behaviour, while 210Pb is a decay product of 222Rn gas, which is a daughter of 226Ra. The relationships between 226Ra and 40K and Ba were weak with correlation coefficient (R) values of 0.31 and 0.01, respectively. The weak correlation between radium and potassium could be explained due to the high potassium solubility. While the weak correlation between radium and barium could be due to the possible input of barium as a result of oil exploration activities in the Northern region, i.e. barium-bearing mud used during drilling operations of oil wells and possible input of radium as a result of phosphate mining activities (Khater et al., 2001; El Mamoney and Rifaat, 2001; Shawky et al., 2001). Vegueria et al. (2002) showed strong correlation between radium isotopes and barium in the water produced from offshore petroleum platforms. The activity ratios of 226Ra/228Ra, 210Pb (gamma)/226Ra, 210Pb(alpha)/226Ra, 210 Pb(alpha)/210Pb(gamma), and radium equivalent activity (Bq/kg) and absorbed Fig. 2. Relationships Between 226Ra and Red Sea shore sediment samples. 232 Th (A), 40 K (B), 210 Pb (C) and Ba (D) concentrations in the M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 161 dose rate in air (nGy/h) are given in Table 3. The average activity ratios standard error (range) of 226Ra/228Ra, 210Pb(gamma)/226Ra, 210Pb(alpha)/226Ra and 210Pb(alpha)/210Pb(gamma) were 1:67 0:02 (0.38–5.33), 1:22 0:10 (0.46– 2.37), 1:48 0:14 (0.53–4.38) and 1:28 0:09 (0.56–2.5), respectively. The average radium equivalent activity (Bq/kg) and absorbed dose rate in air ðnGy=hÞ Table 3 Specific activity ratios of Ra-226/Ra-228, Pb-210/Ra-226 and Pb-210 (alpha analysis)/Pb-210 (gamma analysis), radium equivalent activity (Bq/kg) and absorbed dose rate (nGy/h) in shore sediment samples of the Red Sea coast Ser. Code Ra-226/ Ra-228 Pb-210a/ Ra-226 Pb-210b/ Ra-226 Pb-210b/ Pb-210a Radium— equivalent nGy/h 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 453 455 456 458 459 461 462 463 464 468 469 470 471 473 475 476 501 505 507 508 510 511 515 518 522 524 528 530 531 534 536 538 541 545 548 549 2.70 1.42 1.30 1.71 2.09 1.12 1.52 0.99 1.87 1.19 1.30 1.19 1.52 1.20 0.38 0.39 0.51 0.57 0.67 0.95 1.18 5.33 4.76 1.65 4.67 – 3.59 0.98 1.20 1.80 1.82 1.60 0.83 1.03 1.90 1.39 – 1.31 0.77 0.70 0.83 1.59 – 1.71 – – 0.55 1.41 0.71 1.26 0.58 0.89 0.46 1.33 0.84 1.39 0.47 1.21 2.13 – 1.58 1.34 1.57 0.86 – 2.05 0.84 2.14 1.09 2.37 1.14 1.52 1.14 1.33 1.04 0.56 1.32 1.31 1.14 2.51 – 1.32 0.89 1.51 1.24 1.33 1.46 – – – 1.00 1.79 – 1.20 1.20 0.59 1.75 1.89 1.94 – 0.53 2.67 1.32 4.38 1.28 1.70 – 1.51 – 1.02 1.35 0.80 1.59 0.83 – 1.47 – – 1.62 1.07 1.75 1.05 2.50 – – – 1.19 1.29 – 1.00 0.56 – 1.10 1.41 1.23 – – 1.30 1.57 2.04 1.17 0.72 – 0.99 46.40 19.65 86.86 135.80 49.04 75.70 66.18 42.04 45.87 53.48 77.79 50.11 59.72 54.78 284.69 433.32 442.73 188.38 357.17 84.54 116.94 123.24 38.36 49.09 43.92 16.36 40.02 91.92 121.47 29.78 64.94 32.75 83.02 43.63 52.41 39.35 23.21 8.60 40.50 64.27 23.53 36.02 32.75 20.29 22.50 25.45 34.79 23.41 29.16 25.39 101.5 146.15 155.96 74.65 133.00 39.16 54.75 56.70 19.04 22.15 20.84 8.35 18.72 34.71 48.63 13.79 30.22 16.10 30.78 19.28 25.56 18.01 a b Pb-210 gamma analysis. Pb-210 alpha analysis. 162 M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 standard error (range) were 101:2 18:0 (16.4–442.7) and 41:6 6:15 (8.35– 155.96), respectively. The relationships between 226Ra/228Ra and samples locations are given in Fig. 3. These relationships and their trend lines imply the increase of 226Ra/228Ra activity ratio in the direction of Shuqeir in the North and Safaga where the oil exploration and phosphate mining activities are located. The lowest activity ratios of 226Ra/228Ra and the highest radium equivalent activity and absorbed dose rate were found in the Hurghada—Sharm El-Naga region (sample codes, 475–507) with average values of 0.51, 341.3 Bq/kg and 122.3 nGy/h, respectively. These high values could be explained due to the presence of black sands, which are enriched in the mineral monazite containing a significant amount of 232Th (228Ra). The enrichment occurs because the specific gravity of monazite allows its concentration along beaches where lighter materials are swept away (Cowart and Burnett, 1994). The average value of 232Th/238U (228Ra/226Ra, assuming the secular equilibrium between 238U series and 232Th series and their progenies) activity ratios are 12.35 in pure monazite samples prepared from beach sand of Rosette and 1.4 in beach sand Fig. 3. Relationships between 226Ra/228Ra activity ratio and sample location (Code): (a) Shuqeir–Marsa Alam, (b) Shuqeir–Hurghada, (c) Hurghada–Safaga, and (d) Safaga–Marsa Alam. M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 163 of Rosetta-Egypt. This sand consists of monazite, zircon, thorite, garnet, rutile and other heavy mineral grains. The monazite sand contains high concentration of uranium and thorium, which gave the highest calculated dose rate found there (Ibrahiem et al., 1993; UNSCEAR, 2000). The average activity ratio (range) of 226Ra/228Ra in the north part of the Red Sea (sample codes from 453 to 473) is 1.5 (0.99–2.7). The increase of these ratios above the unity could be attributed to the oil exploration and production processes, and/or to their geo-chemical behaviour in the environment. The average activity ratio (range) of 226Ra/228Ra in the region of Safaga– Quseir–Marsa Alam city (sample codes from 510 to 549) was 2.25 (0.83–5.33). The increases of these ratios, exceeding unity, could be attributed to the phosphate mining in Safaga–Quseir region and/or their geo-chemical behaviour in the environment. Radium is chemically similar to barium and with lesser degree to calcium (Cowart and Burnett, 1994). The previous study on barium concentrations in Red Sea shore sediment samples showed that non-carbonate barium (Ba/CO3) increases from south (Marsa Alam) to north (Shuqeir) at which oil exploration and production processes are present. Oil exploration in the Egyptian Red Sea is mainly restricted to the Gulf of Suez and the northern part of the Red Sea proper. The effect of barium-bearing mud used during drilling operations of oil wells is prominent at Shuqeir City. Other sources of barium could be neglected (El Mamoney and Rifaat, 2001). In Safaga–Qusier region (sample codes 512–528), the average activity ratio of 226 Ra/228Ra was 3.68. The average radium equivalent activity and dose rate were 37.55 Bq/kg and 13.88 nGy/h, respectively; much lower than the average values and that of the Hurghada–Sharm El-Naga region. The high average activity ratio of 226Ra/228Ra could be explained due to the phosphate mining activities in Safaga–Quseir region where the concentration of 238U and its decay products tend to be elevated in phosphate deposits (Khater et al., 2001; NAS, 1999). The average absorbed dose rate in air due to natural radionuclides in the Egyptian soil is 51 and 20–400 nGy/h in areas of high natural radiation background (Monazite sands) (UNSCEAR, 2000). The average activity ratio of 210Pb (alpha)/226Ra is greater than unity, 1.48, and ranged from 0.53 to 4.38. Radium-226 is decaying to 222Rn gas, which is emanating from the geological formation depending on the porosity of the matrix. The mobility of the radon is regarded as one of the main causes of disequilibrium in the uranium decay series (Ivanovich and Harmon, 1992). Also, the 210Pb (222Rn decay product) fallout flux from the atmosphere and/or geo-chemical behaviour of both Pb and Ra in the environment could explain uranium series (U–Ra–Pb) disequilibrium in the environment. Radium forms a complex with chloride and in this form is quite mobile. Conversely, even moderate amounts of sulfate ion inhibit transport because of the co-precipitation of radium sulfate along with barium sulfate. Almost all lead salts are insoluble or sparingly soluble in water (Cowart and Burnett, 1994). 164 M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 The specific activity of 210Pb was measured using two measuring techniques (directly by gamma spectrometry and through 210Po measurement by alpha spectrometry after radiochemical preparation). The results of both techniques are correlated (correlation coefficient ¼ 0:9). The average activity ratio of 210 210 Pbalpha = Pbgamma standard error ðrangeÞ was 1:28 0:09 (0.56–2.5). This deviation from unity could be due to low emission rate and a high self-absorption within the sample matrix of the 210Pb soft gamma ray transition at 46.5 keV. Such self-absorption correction is difficult due to its high degree of dependence on the mineralogical composition of the sample (Hussain et al., 1996). The activities (Bq/kg dry weight) of 238U, 235U, 234U and total uranium, and activity ratios of 234U/238U, 226R/238U and 210Pb/238U are shown in Table 4. The activity ðBq=kg dry weightÞ standard error ðrangeÞ of 238U, 235U, 234U and total U were 25:25 6:82 (9.72–61.98), 2:94 0:33 (2.41–3.54), 25:01 6:79 (8.24–62.56) and 51:52 13:82 (17.96–126.95), respectively. The average activity ratio standard error ðrangeÞ of 234U/238U, 226Ra/238U, 210Pbalpha/238U and 238U/232Th were 1:0 0:05 (0.83–1.26), 0:96 0:17 (0.48–1.55), 0:98 0:18 (0.55–1.55) and 2:0 8 0:90 (0.43–5.61), respectively. The concentration of uranium varies widely in natural waters due to its varied chemical behaviour in response to redox conditions. The oxidised U6+ (uranyl) ion complexes readily with carbonate, phosphate, or sulfate ion and is easily transported in the hydrologic cycle. In reducing waters, U4+ has an extremely strong tendency to precipitate and to remain immobile (Cowart and Burnett, 1994). The behaviour of uranium in aquatic systems is rather conservative and inert. The mean residence time for uranium in seawater is considered to be 5 103 years. Therefore, a relatively homogeneous distribution of uranium should be expected (Holm and Bojanowski, 1989). Although the number of the analysed samples was limited, the uranium concentration varied widely from 9.72 to 61.98 Bq/kg dry weight. The main source of sediments to the beaches of the Egyptian Red Sea is the terrestrial deposits transported from the fringing mountains. The uranium concentration in the shore sediment depends on the uranium concentration in the fringing mountains (crystalline rocks), and the mobility of uranium from the rock and the shore sediment by rain and sea water, respectively (Strezov et al., 1996; El Mamony and Rifaat, 2001). The average activity ratios of 234U/238U, 226Ra/238U and 210Pbalpha/238U are close to unity (1.00, 0.96 and 0.98, respectively), which imply that there is a secular equilibrium between 238U and its progenies in the analyzed samples. The variation in these ratios could be due to the present of varying degrees of disequilibrium between the members of 238U decay series in the coastal marine sediments (Higgy, 2000). Where leaching is less dominant, as in arid regions, the 234U/238U activity ratio become quite high. The key factors in the development of 234U/238U activity ratios out of equilibrium are the relative rate of leaching, mechanical erosion, and daughter half-life. Although the range of 234U/238U activity ratio varies greatly in surface water, often by factor of 2–3, the global average value is closely constrained at 1.2–1.3 (Ivanovich and Harmon, 1992). The activity ratios of Code 453 462 469 470 474 507 512 Ser. 1 2 3 4 5 6 7 U-235 E <2.39 <3.2 2:87 0:8 <3.21 3:54 1:0 2:41 0:5 <2.98 U-238 E 18:62 1:86 9:72 1:5 24:43 1:98 10:44 1:61 18:82 1:74 61:98 3:9 32:77 3:29 18:83 1:87 8:24 1:36 23:56 1:60 10:98 1:65 23:64 2:21 62:56 3:94 27:26 2:88 U-234 E 37:45 2:64 17:96 2:02 50:86 2:68 21:42 2:31 46:00 3:00 126:95 5:57 60:03 4:37 Total U E 1.01 0.85 0.96 1.05 1.26 1.01 0.83 U-234/U-238 – – 0.12 – 0.19 0.04 – U-235/U-238 0.48 0.99 0.83 0.92 – 1.55 – Ra-226/ U-238 0.55 1.13 0.74 1.39 0.55 1.55 – Pb-210/ U-238 Table 4 Specific activity (Bq/kg dry weight) of U-238, U-235 and U-234, and activity ratios of U-234/U-238, U-235/U-238, Ra-226/U-238 and Pb-210/U-238 in shore sediment of the Egyptian Red Sea coast M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 165 166 M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 238 U/232Th varied widely over ten fold (0.43–5.61) with an average value of 2.08. The Th4+ is the only oxidation state of thorium and as such it is quite insoluble. Although transport of thorium in streams can occur by the movement of particulate matter to which the thorium is attached, in general the mobility of thorium is quite restricted (Cowart and Burnett, 1994). So, the geo-chemical behaviour of uranium and thorium could explain the wide variation in their activity ratios in shore sediment samples. The difference in their geo-chemical behaviour in marine environment is very obvious in the Red Sea bottom sediment where 238U/232Th average activity ratio is 40 (Khatir et al., 1998a,b). Statistical analyses of the estimated parameters (activity of different radionuclides and their ratios) of the Red Sea coast shore sediment are given in Table 5. Average activities (range) of 226Ra, 232Th, 40K, 238U and 234U (Bq/kg dry weight) in Red Sea shore sediment and soil, and Mediterranean Sea shore sediment (Alexandria City) and calculated absorbed dose rate (lGy/h) at 1 m above the ground due to natural radionuclides in sediment samples are given in Table 6. Table 5 Statistical summary of estimated parameters of Red Sea Egyptian coast shore sediments Mean Ra-226 Th-232 K-40 Pb-210d Pb-210e U-238 U-235 U-234 U-total Ra-226/Ra-228 Pb-210d/Ra-226 Pb-210e/Ra-226 Pb-210e/Pb-210d U-234/U-238 U-235/U-238 Ra-226/U-238 Pb-210e/U-238 Absorbed dose rate Radium equivalent activity Density CO3 Ba Sr a b c d e SDa SEb Range Unit No.c 24.65 31.41 427.48 25.56 23.90 25.25 2.94 25.01 51.52 1.67 1.22 1.48 1.28 1.00 0.11 0.96 0.98 41.60 101.2 26.00 55.68 213.10 21.34 20.94 18.04 0.57 17.96 36.57 1.19 0.52 0.74 0.43 0.14 0.07 0.39 0.43 36.93 108.1 4.33 9.41 35.52 3.90 3.65 6.82 0.33 6.79 13.82 0.20 0.10 0.14 0.09 0.05 0.04 0.17 0.18 6.15 18.0 5.3–105.6 2.3–221.9 97.6–1011 7.1–81.8 8.1–96.0 9.7–62.0 2.9–3.5 8.2–62.6 18.0–127.0 0.4–5.3 0.5–2.4 0.5–4.4 0.6–2.5 0.8–1.3 0.04–0.19 0.5–1.6 0.6–1.6 8.4–156.0 16.4–442.7 Bq/kg Bq/kg Bq/kg Bq/kg Bq/kg Bq/kg Bq/kg Bq/kg Bq/kg – – – – – – – – nGy/h Bq/kg 36 35 36 30 33 7 3 7 7 35 30 30 2 7 3 5 6 36 36 1.61 33.40 2390.4 3676.9 0.13 22.13 1357.8 2255.4 0.02 3.59 223.2 370.8 1.3–1.8 2.9–1269 183.6–5450 107.7–8073 g/ml % ppm ppm 40 38 37 37 Standard deviation. Standard error. Number of analysed samples. Pb-210 gamma analysis. Pb-210 alpha analysis. M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 167 Table 6 Average specific activities (range) of 226Ra, 232Th, 40K, 238U and 234U (Bq/kg dry weight) in Red Sea shore sediment and soil, and Mediterranean Sea shore sediment (Alexandria City) and calculated absorbed dose rate (lGy/h) at one meter above the ground due to natural radionuclides in sediment samples. 226 Ra Th 40 K 238 U 234 U Absorbed dose rate 232 a b Red Sea shore sediment Red Sea Soil (Oil produced field)a Mediterranean Sea (Alex.) shore sediment b 24.6 (5.2–105.6) 31.4 (2.3–221.9) 427.5 (97.6–1011.3) 25.3 (9.72–62.0) 25.0 (8.2–62.6) 41.6 (8.4–156.0) 194,489 897,803 – 24.0 – – 5.0 (3.0–10.8) 2.1 (0.6–7.8) 46.0 (10.0–86.1) 8.8 (3.6–13.8) 10.7 (3.7–17.5) 48.2 (19.3–117.5) Shawky et al. (2001). Higgy (2000). 4. Conclusions Investigation of the radio-ecological characteristics of the Egyptian coast of the Red Sea and the radiological impacts of the non-nuclear industries (oil industries and phosphate mining) on the coastal environment are needed. The results of our study, which is a part of the national program for nuclear safety and radiation control, are a data-base to distinguish any future changes due to non-nuclear industries on the Red Sea coast. Our results imply that there is an indication of the radiological impacts of the oil industries in the Northern region of the Red Sea coast and phosphate mining in Safaga–Qusier region that need more detailed investigation on the pollution sources and the environmental distribution pattern of different pollutants. We are suggesting to study the impact of phosphate loading on the marine environment near Safaga port and the radio-chemical impacts of salt brines of water desalinization at Hurghada. References Cowart, J.B., Burnett, W.C., 1994. The distribution of uranium and thorium decay series radionuclildes in the environment—a review. Journal of Environmental Quality 23, 651–662. Currie, L.A., 1968. Limits for detection and quantitative determination. Analytical chemistry 40 (3), 586–593. El Mamoney, M.H., Rifaat, A.E., 2001. Discrimination of sources of barium in beach sediments, Marsa Alam to Shuqeir, Red Sea, Egypt. J. King Abdulaziz Univ. Marine Sciences 12, 149–160. Hamilton, T.F., Smith, J.D., 1986. Improved alpha energy resolution for the determination of polonium isotopes by alpha-spectrometry. Applied Radiation and Isotopes 37 (7), 628–630. Hanna, Reg, 1992. The level of heavy metals in the Red Sea after 50 years. Science of the total environment 125, 417–448. Hawkins, J.P., Roberts, C.M., 1993. The growth of coastal tourism in the Red Sea: present and possible future effects on coral reefs. In: Ginsburg, R.N., W. Smith, F.G. (Eds.), In: Proceedings of the Colloquium on Global Aspects of Coral Reefs, Miami, 1993, (university of Miami, RSMAS), 1994, pp. 385–391. 168 M.H. El Mamoney, A.E.M. Khater / J. Environ. Radioactivity 73 (2004) 151–168 Higgy, R.H., 2000. Natural radionuclides and plutonium isotopes in soil and shore sediments onAlexandria Mediterranean Sea coast of Egypt. Radiochim Acta 88, 47–54. Holm, E., Bojanowski, R., 1989. Natural activity in the Baltic Sea. In: The Radioecology of Natural and Artificial Radionuclides, Proceeding of the XV Regional Congress of IRPA, Vishy, Sweden, pp. 49–54. Hussain, N., Kim, G., Church, T.M., Carey, W., 1996. A simplified technique for gamma-spectrometric analysis of 210Pb in sediment samples. Applied Radiation and Isotopes 47 (4), 473–477. Ibraheim, N.M., Abd El Ghani, A.H., Shawky, S.M., Ashraf, E.M., Farouk, M.A., 1993. Measurement of radioactivity levels in soil in the Nile Delta and Middle Egypt. Journal Health Physics 64 (6), 620–627. Intergovernmental Oceanographic Commission (of UNESCO), 1997. Regional blueprint and pilot projects for the Red Sea, Fourth Session of the GOOS Health of the Oceans Panel, the National University of Singapore, 13–17 October 1997. (http://ioc.unesco.org/ goos/hoto4_toc.htm). Ivanovich, M., Harmon, R.S., 1992. Uranium Series Disequilibrium: applications to Earth, Marine and Environmental Sciences, second ed . Clarendon press, Oxford. Khater, A.E.M., 1997. Radiological study on the environmental behaviour of some radionuclides in the aquatic ecosystem. Ph.D. thesis, Cairo University. Khater, A.E.M., Ashraf, R.H.H., Pimpl, M., 2001. Radiological impacts of natural radioactivity in Abu Tartor posphate deposits, Egypt. Journal Environmental Radioactivity 55, 255–267. Khatir, S.A., Ahamed Mustafa, M.O., El-Khaangi, F.A., Nigumi, Y.O., Holm, E., 1998a. Radioactivity levels in the Red Sea coastal environment of Sudan. Marine Pollution Bulletin 36 (1), 19–26. Khatir, S.A., El-Ganawi, A.A., Ahamed, M.O., El-Khaangi, F.A., 1998b. Distribution of some natural and anthropogenic radionuclides in Sudanese harbour sediments. Journal of Radioanalytical and Nuclear chemistry 237 (1–2), 103–107. National Academy of Science (1999). Evaluation of guidelines for exposure to technologically enhanced naturally occurring radioactive materials. http://www.nap.edu/ openbook/0309062977. Pimpl, M., Yoo, B., Yordanoua, I., 1992. Optimisation of radioanalytical procedure for the determination of uranium isotopes in environmental samples. Journal of Radioanalytical chemistry 161 (2), 493–501. Said, R., 1990. The geology of Egypt, A.A. Balkema/Rotterdam/Brookfield. Shawky, S., Amer, H., Nada, A.A., Abd El-Maksoud, T.M., Ibrahium, N.M., 2001. Characteristics of NORM in the oil industry from Eastern and Western deserts of Egypt. Applied Radiation and Isotopes 55, 135–139. Strezov, A., Yordanov, M., Pimpl, M., Stoilova, T., 1996. Natural radionuclides and plutonium content in Black Sea bottom sediments. Journal of Health Physics 70 (1), 70–80. United Nations Scientific Committee on the Effects of Atomic Radiation, (2000). Sources and effects of ionising radiation. Report to the general assembly with annexes, UNSCEAR 2000. United States Department of Energy, 1992. EML procedures manual. Report HASL 300. Vegueria, Jerez, S.F., Godoy, J.M., Miekeley, N., 2002. Environmental impact study of barium and radium discharges by produced waters from the ‘‘Bacia de Campos’’ oil-field offshore platforms, Brazil. Environmental Radioactivity 62, 29–38. DETERMINATION OF LEAD-210 IN ENVIRONMENTAL SAMPLES USING DIFFERENT RADIO-ANALYTICAL TECHNIQUES Yasser Y. Ebaida and Ashraf E.M. Khaterb & c∗ Physics Department, Faculty of Science, Fayum, Cairo University, Egypta, National Center for Nuclear Safety and Radiation Control, Atomic Energy Authority, Egyptb & Physics Department, College of Sciences, King Saud University, Riyadh, Kingdom of Saudi Arabia ABSTRACT: Measurement of 210 Pb has gained a highly scientific attention basically due to its wide range of environmental applications. The most commonly used analytical techniques; gamma spectrometry, beta counting and alpha spectrometry techniques were used to measure different types of environmental samples (geological, soil, sediment). Our paper is aimed at comparing the capabilities and limits of application of these three different analytical techniques for 210 Pb measurement in different environmental samples. In addition to the systematic view of methodical principles and details, analytical data of 210 Pb measurements in the samples, the three different techniques (gamma spectrometry, beta counting and alpha spectrometry) are discussed to highlight the degree of comparability of the data sets and most probable sources of results discrepancies and errors. Based on the demanded investigation, one analytical technique will be chosen for routine analysis, while the other techniques, if they are available, could be used for analytical quality assurance measures. Therefore, it was essential to compare the analytical efficacy of each technique, which differ concerning the reachable detection limit (MDA), sensitivity, analytical effort, complete analysis duration and waiting period before analysis. ∗ Corresponding author: present address; Physics Department, College of Sciences, King Saud University P.O. Box 2455, Riyadh 11451 Kingdom of Saudi Arabia. Fax: +966 1 4676 379. Email: [email protected] 1. INTERODUCTION: Lead-210 is a very useful radioactive element for environmental studies. Measurements 210 of 210 Pb have found extensive applications in the Pb geo-chronometry (measuring the sedimentation rates) of rapidly accumulating sediments in lakes, estuaries and the coastal marine environments.1-10 Measurement of 210 Pb in air and in surface soils will afford quantitative information about the flux of radon gas (222Rn) and its daughters in the atmosphere.11-16 It can help in uranium exploration and monitoring transfers of radionuclides of uranium series in soils and aquatic systems. In the context of luminescence dating, the 210Pb/226Ra activity ratio can give the proportion of 222 Rn that can escape from given sediment, such data being important in the calculation of annual radiation dose rate. Also, 210 Pb and its grand-daughter radionuclide (210Po) are included in the group of most highly toxic radioisotopes and provide the major internal natural radiation dose to man. It is approximately 18% of the average dose to the population from internal irradiation due to ingested radionuclides. For some members of the public the dose due to ingestion of 210 Pb and 210 Po may be far higher due to high intakes of specific foodstuffs such as shellfish. 17-19 Lead-210 (physical half-life time, 22.2 y) occurs naturally as one of the decay products of the 238U series. Disequilibrium between 210Pb and its parent nuclide, 226Ra (physical half-life time, 1600 y), arises through the diffusion of the intermediate gaseous isotope, 222Rn (physical half lifetime, 3.8 d). A fraction of 222Rn atoms diffuse into the atmosphere and its decay products (mainly 210 Pb and its daughter 210Po) are removed from the atmosphere by wet and dry deposition.18 Lead-210 decays by combined emission of weak beta and gamma rays and internal conversion electrons to the ground state of 210 Bi (5 days half life time), which in turn decays by emission of beta particles to a pure alpha emitter 210 Po, as shown in Fig 1. Because of the significant self-absorption of the weak beta particles of 210Pb and 210Bi (beta max 16 and 63 keV) and the alpha particles of 210 Po (5.3 MeV), lead-210 measurements are frequently including lead and polonium radiochemical separation prior to their individual analyses.20 A number of analytical techniques are available for the measurement of 210Pb, based on different physical and chemical principles. They differ concerning the reachable detection limit, selectivity, analytical effort, reproducibility and stability against differing chemical composition and levels of other natural radionuclides. There are three commonly used radiometric methods for measurement in the environmental samples, which are gamma-ray spectrometry of 210 Pb 210 Pb, which allows direct measurement in various media, including water, rocks, soil and sediment; beta counter and spectrometry, observing the growth of its daughter spectrometry of its grand-daughter 210 Bi; and alpha particle 210 Po, assuming radioactive equilibrium between the two radionuclides.18,19,22 A systematic view of methodical principles and details of the 210Pb measurement methods is a prerequisite to compare the analytical power of the different techniques, to guarantee the comparability of the results from these different methods and to know the probable sources of data discrepancies and errors.19 This work is aimed at comparing the capabilities of different techniques (gamma spectrometry, beta counting and alpha spectrometry) for 210 Pb determination and their limits of application for the purposes of environmental samples analyses. 2. EXPERIMENTAL WORK: 2.1. Sample preparation: The first step of analysis involves sample matrix drying at an oven temperature lower than 100 oC, crushing, grinding and sieving through 2 mm sieve mesh size. For ashing, 10 grams of the dried sample was moisture with nitric acid (HNO3) till no further reaction occurs. The sample was dried on a sand bath then ashed at 550 0C for 6-8 hours. If the sample residue was not free of organic carbon, which can be recognized by a dark brown or black colored ash, the ashing process had been repeated again. Finally the sample ash was ground and homogenized. 2.2. Synopsis of the analytical techniques for the determination of 210 Pb in environmental samples: 2.2.1. Gamma spectrometry; The dried samples were transferred to polyethylene containers of 100 cm3 capacity. Lead-210 specific activities were measured using well calibrated gamma spectrometry based on hyper pure germanium (HpGe) detectors. The HpGe detector had a relative efficiency of 40% and full width at half maximum (FWHM) of 1.95 keV for 60Co gamma energy line at 1332 keV. The gamma transmissions used for activity calculations was 46.5. keV with a branching ratio of 4.05 %. The gamma spectrometers were calibrated using Pb-210 standard solution in the same sample- detector geometry.23 The lower limit of detection, with 95% confidence, is 0.44 Bq for 1000 minute measuring time.24 2.2.2. Beta counting; One milliliter of Pb2+ carrier (20 mg/ml) is added to 3-5 g of the ashed sample and then dissolved using mineral acids (HNO3, HF and HCl). Lead is leached with hydrobromic acid (HBr) as tetrabromo-complex, extracted with trioctylamin/toluene and backextracted with HCl. After addition of Bi3+ carrier, Bi3+ traces are separated by precipitation as BiOCl. Finally lead is precipitated as PbCrO4 and collected on a filter paper. The chemical recovery of Pb-210 on the filter was determined gravimetrically. After waiting for 8-10 days, the filter is covered with a filter paper of equal size to hold back the low energy beta particles of 210Pb and the alpha particles of ingrown 210 Po. The high energy beta particles of 210 Bi (1.2 MeV) are counted using a calibrated low background gas proportional counter. The counter was calibrated using 210Pb standard solution sources prepared in the same condition as the analyzed samples. The counting efficiency is about 40% and the lower limit of the procedure, with 95% confidence, is 7 mBq/sample for 1000 minute counting time.24 The details of the analytical steps are given in Fig 2. 2.2.3. Alpha spectrometry; The dried sample (1-2 g) is spiked, for chemical recovery and activity calculation, with about 80 mBq 208 Po and dissolved using mineral acids (HNO3, HF and HCl). Finally the sample residuals is dissolved in about 30 ml 0.5 M HCl. The sample is heated to 85oC and about 100 mg of ascorbic acid is added to the hot solution to reduce the iron Fe(III) to Fe(II). Then, polonium isotopes are auto-deposited from the solution at temperatures between 80 –90 oC onto rotating, clean mirror finishing, stainless steel disk fixed in a Teflon disk holder25,26. The plated disk is measured using alpha spectrometer (CANBERRA 4701 vacuum chamber) based on passivated implanted planar silicon (PIPS) detector with 450 mm2 surface area, about 25% counting efficiency and 20 keV resolution for 241Am alpha energy at 5.48 MeV, and connected up to a computerized multichannel analyzer (MCA) operating with Genie 2000 software (CANBERRA). The average chemical recovery is 75 %, and the individual values ranged from 50 to 100%. The sample is measured for 1000 minutes, applying a lower limit of detection of 1 mBq, with 95% confidence.24 The details of the analytical steps are given in Fig 3. 3. RESULTS AND DISCUSSION: Comparison of the main parameters of the three different analytical techniques, gamma spectrometry, beta counting and alpha spectrometry, which are commonly used for the determination of 210 Pb in environmental samples, is given in table 1. They differ over a wide range of analyzed sample sizes and counting system background and minimum detectable activities (MDA). It is noticeable that the alpha spectrometry technique achieves the lowest MDA (1 mBq/sample), amongst the three analytical techniques. While the MDA for gamma spectrometry is the highest amongst all three techniques. Concerning the time duration of the 210 Pb complete analysis (source preparation and measurement); it is ranged from one day for gamma spectrometry to more than 10 days for beta counting technique. While for alpha spectrometry, the complete analysis duration is at least three days for sample dissolution, alpha source preparation and alpha spectrometry, and varied widely according to the time of sample dissolution that depends on sample type. Also, the time needed before starting sample analysis differs and depends on the used analytical techniques. Analysis of 210 Pb using both gamma spectrometry and beta counting is possible without time delay before starting the analysis. For alpha spectrometry, the time delay before analysis depends on 210 Pb-210Po secular equilibrium condition in the sample. If the secular equilibrium is already existed, the samples could be analyzed without time delay. Otherwise, It is essential to first get rid of samples via either auto plating of Accordingly, 210 Po existed in the 210 Po on a stainless steel disk or sample ashing at 600 oC.27 210 Po can be analyzed after 3-6 months delay time. It should be mentioned that the ingrowth factor of 210 Po as a decay product of 210 Pb during the storage time should be taken into consideration. Ideally, to be sure of reaching secular equilibrium, the sample should be stored at least for two years, especially for samples with expected higher 210 Po concentration than that of 210 Pb. Three aspects should be considered to evaluate the methods with respect to the demanded investigations. (i) The attainable detection limit decides whether a method is successfully applicable at all for the investigations. (ii) The duration of a complete analysis can exclude methods of longer duration if there is an urgent need for the results. (iii) The total expenditure in work and equipment has to be considered if economic limitations are important.22 Based on these aspects one method is chosen for 210Pb routine measurements for the demanded investigation but as necessary measures of analytical quality assurance some selected samples should be measured using another analytical technique. To guarantee the comparability of the results from these different analytical methods, the advantages and disadvantages of each method and the sources of data discrepancies and errors should be cleared. In this work, it is planned to apply these aspects using 210 Pb measurement results of some selected geological, processed geological, soil and sediment samples. The gamma-ray spectrometric analytical technique; Its main advantages are being fast, nondestructive, relatively simple sample preparation with no need of preliminary chemical separation, and direct analysis without delaying time through the measurement of 46.5 keV gamma energy transition. However, the main disadvantages are its relatively high MDA and the often difficult corrections for self-attenuation in the sample matrix.28-30 The relative high MDA of gamma spectrometry technique is due to both the low emission probability (4.05%) and low energy transition of gamma line. For a given sample container volume and geometry, the selfattenuation can significantly vary from sample to sample because it depends strongly on both the composition and apparent density of the sample.29 Self-attenuation can be theoretically calculated using physical models of interaction between gamma-rays and matter, computed with a Monte Carlo technique. Alternatively, some experimental approaches have been proposed and mentioned by Pilleyre et al. (2006). One approach dealt with the determination of absolute activity of large volume geological samples, without being hindered by self-attenuation. It was based on replicate counting of increasing volumes of the unknown samples. Good results were obtained but it was time consuming. Another approach have reported a method based on an evaluation of the transmission of low-energy gamma-rays from a 210Pb point source placed on an aluminum container in the presence and absence of the sample. In addition, others attempted to establish a direct correspondence between the measured count rate for the sample and the count rate expected for material identical to that used for efficiency calibration using gamma ray transmission; this was for measuring 241Am (at 59.6 keV), where the situation is nearly the same as for 210Pb.19 The Beta-particle counting of 210Bi technique; The main advantage is the relatively lower limit of detection, in the range of several mBq per sample. The main disadvantages are being destructive, the need of radio-chemical separation and beta particle source preparation, the need of waiting 10-30 days in order to count the prepared source and indirect measurement of 210 Pb in the analyzed samples. There are different analytical methods for lead separation such as ionexchange method with EIChrome Sr. Spec. resin or Dowex 1x8 resin, and solvent extraction methods with diethyl dithiocarbanic acid (DDTC) or trioctylamin/toluene. The lead reagent, which is used as a yield tracer (carrier), could be a source of error. Clayton (1995) had analyzed a sample of lead of Tudor origin (virgin) and modern commercial reagent grade lead nitrate and the specific activity of 210 Pb-210Po were 10.9 ± 0.7 and 500 ± 40 Bq/kg lead respectively.19 The specific activity of 210Pb-210Po in the lead nitrate, which used in our analysis, is 18.2 ± 2.3 Bq/kg (29.1 ± 3.7 Bq/kg lead), as shown in Table 5. The alpha spectrometry of 210 Po technique; The main advantages are the excellent low limit of detection (in the range of few mBq per sample), the selectivity of polonium platting onto the stainless steel disk and the relatively less chemical preparation steps compared to that is associated with beta counting. Waiting time required to achieve the analysis, being destructive and the need for careful chemical treatment are considered as the main disadvantages of this technique.31,32 Specific activity of 210Pb (Bq/kg) in geological, processed (geological samples have been exposed to some physical and chemical processing) and soil, and sediment samples, and their average are given in Tables 2, 3 and 4 respectively and shown in Fig. 4. The relationships and data correlations of 210 Pb specific activity that were measured using three different analytical techniques (gamma spectrometry, beta counting and alpha spectrometry) in all samples and in each sample type (i.e. geological, processed, soil and sediment) are shown in Fig 5 and 6, respectively. For the geological and processed samples, the existence of some discrepancies (but not vivid) in the results of some samples (specially the geological and processed samples) obtained from the different techniques was noticed. On the contrary, soil samples results showed acceptable concurrence amongst the different techniques. For sediment samples, the 210Pb specific activity measured using gamma spectrometry and alpha spectrometry has trend of comparability of the results, although some samples has a higher concentration of 210 Pb using one technique more than the other, without the existence of clear trends, as shown in Fig 4. Generally the average specific activity of 210Pb in each sample type for each analytical technique and its over all average (for all samples of the same type and all analytical techniques) are mostly comparable and within the error values, as shown in Fig 4. It is obvious that the specific activity of 210 Pb measured using alpha spectrometry of 210Po is slightly higher than that was measured by gamma spectrometry and could be explained by the sample self-attenuation. The sample self attenuation correction has not been applied for our gamma measurements. The results obtained for all samples by the different techniques, Fig 5, are strongly correlated with correlation coefficients (R2) very close to unity. The difference between the data linear fitting and the dashed line, represents the assumed identical results, is clear especially for highly active samples (geological and processed samples) where the alpha spectrometry results seemed higher than that obtained by gamma spectrometry. These differences could be explained by the expected self attenuation in some samples. Accordingly, careful efficiency calibration should be carried out to elude this problem. On the other hand, another issue concerning self attenuation problem should be considered, where empirical and experimental methods could be used to take the self attenuation in the lower energies region into consideration.21,29 The specific activity of 210 Pb in each sample type using three analytical techniques is shown in Fig 6. The correlation coefficient between gamma and alpha spectrometry measurements are stronger than that between gamma spectrometry and beta counting measurements. These discrepancies are very clear for soil samples without any clear reason. It is well known that gamma spectrometry measurements are performed using bulk amounts of samples, so, the homogeneity issue does not bother the analysts. On the other hand, regardless of their good MDA, both alpha and beta spectrometry techniques are performed based on a relatively smaller sample size. So, this might brings up the homogeneity problem. Regarding the geological and processed geological samples, the discrepancies in the results among the three techniques could be explained by the lack of sample homogeneity and the existence of hot spots. This could be more clear in the case of the processed samples since they are both physically and chemically (washed) treated. Twenty eight sediment samples were analyzed using two different techniques (gamma and alpha spectrometry) are given in Table 3 and shown in Fig 4. The correlation coefficient was calculated for these the two sets of results and was 0.9. Some samples showed good agreement for both techniques (samples 8, 10 11, 16, 17 and 18), Fig 5 and 6. However, other samples showed distinct discrepancies. The homogeneity problem may be a major factor, in addition to the necessity of sample self attenuation correction that was not corrected in all of our results. The specific activity of 210Pb in some selected reference materials using gamma and alpha spectrometry techniques are given in Table 5 and shown in Fig 7. The results are showing good accuracy for both techniques compared to the given reference values. One reference sample was analyzed using both techniques and they gave a spectacular agreement, though relatively lower than the reference value but it falls within the reference range. It should be mentioned that the IAEA reference samples often follow a tedious procedure of mixing and strict homogeneity tests prior to releasing to laboratories for use as reference materials. So, these results are considered supportive of our point of view regarding the homogeneity issue. 4. CONCLUSIONS: For 210 Pb analysis in environmental samples, the three analytical techniques should give comparable results for the same sample set. For routine analysis, the used analytical technique should be chosen carefully based on each technique advantage and disadvantage, and the analysis requirements. Gamma spectrometry analytical technique is easier, needs less man-power and cost than the other techniques. It is direct measurement of 210 Pb in a relatively large volume sample with no waiting time before analysis and minor effect of sample inhomogeneity problem. However, its major advantages are its relatively high Minimum Detection Activity (MDA), about 0.44 Bq/sample, and the necessity to correct the counting efficiency for the gamma ray attenuation due to sample matrix and composition. Beta counting analytical technique needs tedious chemical work and waiting time (2-3 weeks) before measurement for 210 Bi build up in the sample source, but no waiting time needed before sample analysis. Its MDA (0.007 Bq/sample) is much lower than that of gamma technique. So it is considered moderate regarding the time consumption. Alpha spectrometry analytical technique needs relatively simple chemical sample treatment and source preparation and no waiting time before measurement. It needs also to ensure a certain degree of equilibrium between 210Pb and its grand-daughter 210Po, which requires waiting for 3-6 months after the first enrichment of 210 210 Po to Po analysis or two years especially for the sample with an expected 210 Pb. Its MDA (0.001 Bq/sample) is the lowest amongst the three techniques. On the other hand, using a relatively small size of the sample for Beta counting and alpha spectrometry analytical techniques could increase the analytical error due to the possible lack of sample homogeneity. Therefore, it is recommended for the analysts to determine exactly their needs and to know a little about the samples history to be able to decide on the best analytical technique to use for each specific sample or set of samples. For instance, if the analyst is given a sample with expected high 210Pb specific activity sample, gamma spectrometry technique is strongly recommended. On the other hand if the samples are expected to have a relatively low 210 Pb specific activity, either alpha spectrometry or beta counting techniques are recommended. The choice between the alpha spectrometry and beta counting technique could be decided based on the accuracy needed and the time limits for the analyst. 5. 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Table 1: Comparison of parameters of different analytical techniques for the determination of 210Pb in environmental samples Method Gamma-ray spectrometry Beta counting Alpha spectrometry Sample size (g) 100 5 1-3 Counting time (min.) 1000 1000 1000 Sensitivity, s-1Bq-1 2.9 x 10 -4 2.5 5 Background (cpm) 0.5 0.5 0.005 7 40 20 440 7.1 1 1 day > 10 days 3-6 moths+ Counting efficiency % MDA* (mBq) in 1000 min. Duration of complete analysis * MDA: minimum detectable activity + 3 days, in case of Pb-Po secular equilibrium existence Table 2: Specific activity of 210Pb (Bq/kg) in geological, processed and soil samples using different analytical techniques. Method Sample G 1+ G2 G3 P 1++ P2 P3 P4 S 1+++ S2 S3 S4 S5 Gamma spectrometry A* ± E** 279.0 ± 5.6 34.8 ± 3.8 64.9 ± 5.3 251.0 ± 14.8 154.0 ± 6.9 202.0 ± 14.1 173.0 ± 17.3 19.8 ± 5.8 20.7 ± 5.2 15.1 ± 0.8 25.4 ± 4.8 31.6 ± 5.1 * Specific activity (Bq/kg) ++ Beta counting A 251.3 43.0 65.2 216.1 277.4 290.1 116.7 14.0 17.4 15.1 18.3 17.2 ± ± ± ± ± ± ± ± ± ± ± ± ± E 2.7 0.9 1.0 1.9 3.3 2.8 1.3 0.7 0.6 0.8 0.8 0.7 Alpha spectrometry A ± E 396.3 ± 12.6 36.5 ± 2.4 85.3 ± 4.3 355.9 ± 10.7 236.9 ± 11.4 300.6 ± 8.6 234.2 ± 7.2 19.1 ± 1.1 23.6 ± 1.3 19.2 ± 1.0 21.1 ± 0.9 21.3 ± 1.1 ** Error (Statistical and counting Error only) Processed sample (Physical treated geological samples) +++ Soil sample + Geological sample Table 3: Specific activity of 210 Pb (Bq/kg) in sediment samples using gamma-ray and alpha spectrometry techniques. Ser. No. Pb-210* ± E* Pb-210** 1 29.34 ± 3.4 73.35 ± 3.4 2 13.95 ± 1.37 18.78 3 80.99 ± 3.13 4 9.88 5 ± E Ser. No. Pb-210* ± E Pb-210* 15 23.71 ± 3 17 ± 1.6 ± 1.2 16 81.75 ± 5.1 81.41 ± 4.3 96.01 ± 5.7 17 14.63 ± 1.5 14.51 ± 0.9 ± 1.02 15.71 ± 0.8 18 29.63 ± 2 32.68 ± 1.7 19.5 ± 1.94 16.09 ± 1.3 19 8.72 ± 1.1 12.29 ± 1.4 6 24.5 ± 5.6 28.8 ± 2.1 20 24.8 ± 6.7 33 ± 3.2 7 11.08 ± 0.98 17.97 ± 1.3 21 16.93 ± 1.8 22.04 ± 1.9 8 13.54 ± 1.42 14.49 ± 1.2 22 14.82 ± 1.8 23.26 ± 1.1 9 21.1 ± 7.0 25.2 ± 2.5 23 22.1 ± 5.1 24.7 ± 2.4 10 14.07 ± 1.22 14.83 ± 1.2 24 29.63 ± 3.3 34.75 ± 2.6 11 7.9 ± 0.79 8.07 ± 0.7 25 9.44 ± 0.8 13.86 ± 1.1 12 25.61 ± 2.59 31.61 ± 4.7 26 19.76 ± 2.2 25.42 ± 2.9 13 7.08 ± 0.9 12.38 ± 1.3 27 11.4 ± 1.4 23.31 ± 2.4 14 22.05 ± 3.58 17.54 ± 1.3 28 23.71 ± 2.6 13.39 ± 1.5 * Statistical and counting Error only ± E Table 4: Average specific activity of 210Pb (Bq/kg) in different environmental samples using different analytical techniques Pb-210, Bq/kg Sample type Gamma Spectrometry Beta counting Alpha spectrometry Average Geological 126.2 ± 76.9, 133.2* 119.8 ± 66.0, 114.4 172.0 ± 112.7, 195.2 139.6 ± 16.7, 28.9 (34.8 - 279.0) [3]+ (43.0 - 251.3) [3] (36.5 - 396.3) [3] (119.8 - 172.7) [3] 195.0 ± 21.1, 42.3 225.1 ± 39.6, 79.2 281.9 ± 29.1, 58.1 234.2 ± 25.4, 44.1 (154.0 - 251.0) [4] (116.7 - 290.1) [4] (234.2 - 355.9) [4] (195.0 - 281.9) [4] 22.5 ± 2.8, 6.3 16.4 ± 0.8, 1.8 20.9 ± 0.8, 1.8 19.9 ± 1.8, 3.2 (15.1 - 31.6) [5] (14.0 - 18.3)[5] (19.1 - 23.6) [5] (16.4 - 22.5) [5] 22.7 ± 3.4, 18.0 - 27.2 ± 4.0, 21.3 24.9 ± 2.3, 3.2 (7.1 - 81.8) [28] - (8.1 - 96.0) [28] (22.7 - 27.2) [28] Processed geological Soil Sediment * Average ± standard error, standard deviation + (range) [number of samples] Table 5: Comparison of the specific activity of 210 Pb (Bq/kg) in some selected reference material samples using gamma and alpha spectrometry and their reference values Methods Gamma spectrometry Alpha spectrometry Samples A* ± E** A±E IAEA-384, sediment (1)& 23.5 ± 1.3 - 23.5 (22.2-24.2) IAEA-326, soil (4) 43.4 ± 6.7 43.14 ± 2.02 52.5 (47.9-57.1) - 51.8 ± 4.8 58.8 (53.9-63.7) 50.61 ± 7.58 - 48 (42.2-54.1)+ - 5092 ± 283 IAEA-327, soil (2) IAEA-135, marine sediment (2) IAEA-RGU, uranium ore (2) Lead Nitrate, Pb(NO3)2++, Analytical grade (2) * Specific activity (Bq/kg) ++ Used as carrier - & (number of analysis) 4914 (4844-4984) 18.17 ± 2.32 ** Error (Statistical and counting Error only) Reference value - + Information value 210 Pb (22.3 y) β-, 16& 63 keV γ, 46.5 keV 210 Bi (5 d) β-, 1.2 MeV 210 Po (138 d) α, 5.3MeV 206 Pb (Stable isotope) Figure 1: Decay chart of 210Pb Ashed Sample M aterial add yield tracer Pb 2+ digest with HNO 3 , HCl and HF fum e off with HBr (47%) leach with 3 M HBr Dissolved Sample Solution Aqueous phase: discard Extraction with TOA/Toluene Organic phase: wash with 0.1 M HBr O rganic phase: Back-extraction with HCl (32%) discard Aqueous phase: wash with CHCl 3 add Bi3+ - carrier and HNO 3 evaporate to dryness dissolve in HCl(32% ) dilute with H 2 O , adjust pH=8 with NH 3 Bi/Pb- Precipitation supernatant solution: discard dissolve precipitation with HCl (32%) dilute with H 2 O Pb/Bi- Precipitation Note date and tim e filtrate, discard the precipitation add 5 g CH 3 COO NH 4 heat to boiling, add Na 2 CrO 4 solution PbCrO 4 - Precipitation Filtrate W ash filter with Ethanol/Acetone Determ ine chem ical yield by weighing After 8-10 days Cover precipitate w ith filter paper Gross- Beta M easurement Calculate 210 Pb activity from m easured 210 Bi activity Figure 2: Flowchart of the radiochemical analysis of 210Bi (210Pb) by Beta counting technique Dried Sample Material Add yield tracer 208Po or 209Po Digest with HNO3, HCl and HF Fume off with HCl (32%) Dissolve in 0.5 M HCl Dissolved Sample Material Heat to boiling, Add 200 mg Ascorbic acid Po deposition on a rotating stainless steel disk Polonium auto-platting onto rotating disk for one hour at 90 oC Alpha Spectrometry Figure 3: flowchart of the radiochemical analysis of 210Po (210Pb) by alpha spectrometry 40 450 Gamma spectrometr Alpha spectrometry Beta counting 35 Specific activity of 210Pb (Bq/kg) Specific activity of 210Pb (Bq/kg) 400 350 300 250 200 150 100 Gamma spectrometry Alpha spectrometry Beta counting 50 30 25 20 15 10 5 0 0 G1 G2 G3 P1 P2 P3 S1 P4 S3 S4 S5 Soil samples Geological and processed samples 350 100 Gamma spectrometry Alpha spectrometry Gamma spectrometry Beta counting Alpha spectrometry Average 300 90 250 Specific activity of 210Pb (Bq/kg) Specific activity of 210Pb (Bq/kg) S2 80 70 30 20 10 200 150 100 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Sediment samples Geological Processed Soil Sediment Sample types Fig 4: Specific activity of 210Pb in different environmental samples (geological, processed geological, soil and sediment) using different analytical techniques (gamma spectrometry, beta counting and alpha spectrometry) 400 550 500 350 Alpha spectrometry 350 Y = 1.35 X 2 R = 0.99 Alpha spectrometry 400 40 300 35 Y = 1.12 X 2 R = 0.58 250 30 Alpha spectromtery 200 150 100 50 300 250 200 150 25 100 100 20 150 200 250 300 350 400 Gamma spectrometry 15 0 10 -50 5 -100 -100 Y= 1.44 X 2 R = 0.99 (a) 450 0 -50 0 50 100 150 200 250 300 350 0 5 10 15 20 25 30 35 40 Gamma spectrometry Gamma spectrometry 300 300 (c) (b) 250 Y= 1.04 X 2 R =1 Beta counting 200 Beta counting 250 150 100 200 150 100 50 50 0 0 0 50 100 150 200 Gamma spcetrometry 250 300 Y = 0.73 X 2 R=1 0 50 100 150 200 250 300 350 400 450 Alpha spectrometry Figure 5: Correlations between the specific activity of 210Pb in environmental samples using three different analytical techniques 450 25 450 Alpha spectrometry Beta counting (a) Geological and processed samples 400 (b) Soil samples 24 400 linear fit of alpha spec. 2 R = 0.2 Y=17.9+.12X 300 Liner fit of alpha spec. 2 R = 0.99 Y=- 8.59+1.47X 250 200 250 200 Liner fit of beta counting 2 R = 0.59 Y = - 34.2 + 0.88X 150 150 100 22 21 Beta counting 300 Alpha spectrometry 350 Beta couting Alpha spectrometry 23 350 20 19 18 17 16 100 linear fit of beta couning 2 R =0.31 Y=12.8+0.16X 15 50 50 0 0 Alpha spectrometry Beta counting 14 0 50 100 150 200 250 13 300 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Gamma spectrometry Gamma spectrometry 400 Alpha spectrometry linear fit 95% confidence limit 200 Linear fit of beta counting 2 R = 0.98 Y= -0.78+0.85X 100 Beta counting Linear fit of alpha spec. 2 R =0.99 Y=-5.85+1.44X Alpha spectrometry 80 300 Alpha spectrometry (c) Sediment samples 100 Alpha spectrometry Beta counting (d) All samples Y= 1.16 X 2 R = 0.81 35 30 25 20 15 10 5 0 0 0 50 100 150 200 Gamma spectrometry 250 300 -5 0 5 10 15 20 25 30 35 60 70 80 90 Gamma spectrometry Fig 6: Correlations between the specific activity of 210Pb in different environmental samples types using three different analytical techniques Gamma spectrometry Alpha spectrmetry Reference value Uranium ore 5000 specific activity of 210 Pb (Bq/kg) 6000 Soil Soil 60 Sediment 40 Sediment 20 0 IAEA 384 IAEA326 IAEA 327 IAEA 135 RGU Refrence samples Fig 7: Specific activity of 210Pb (Bq/kg) in some selected reference samples using different analytical techniques with their reference values Journal of Environmental Radioactivity 75 (2004) 47–57 www.elsevier.com/locate/jenvrad Occupational exposure of phosphate mine workers: airborne radioactivity measurements and dose assessment Ashraf E. Khater , M.A. Hussein, Mohamed I. Hussein National Center for Nuclear Safety and Radiation Control, Atomic Energy Authority, P.O. Box 7551, Nasr City, Cairo 11762, Egypt Received 1 June 2003; received in revised form 1 September 2003; accepted 1 October 2003 Abstract Under the Egyptian program for radiation safety and control, airborne radioactivity measurements and radiological dose assessment were conducted in some phosphate and uranium mines. Abu-Tartor mine is one of the biggest underground phosphate mines in Egypt. Airborne radioactivity, radon (222Rn) and its short-lived decay products (progenies) and thoron (220Rn), were measured in selected locations along the mine. The environmental gamma and workers dose equivalent rate (mSv/y) were measured inside and outside the mine using thermo-luminescence dosimeters (TLD). The results were presented and discussed. The calculated annual effective dose due to airborne radioactivity is the main source of occupational exposure and exceeding the maximum recommended level by ICRP-60 inside the mine tunnels. A number of recommendations are suggested to control the occupational exposures. # 2004 Published by Elsevier Ltd. Keywords: Occupational exposure; Phosphate; Airborne Radioactivity; Dose calculation 1. Introduction Among the decay products of uranium, special attention has been directed towards radon (222Rn), a noble gas, that disseminates into the atmosphere and reaches radioactive equilibrium with its relatively short-lived daughters in about 2 h. Its highenergy alpha particles are known to contribute substantially to the induction of lung neo-plasias and skin cancer (Santo et al., 1995). Phosphate rock is the starting raw Corresponding author. Tel./fax: +20-2-274-0238. E-mail address: [email protected] (A.E. Khater). 0265-931X/$ - see front matter # 2004 Published by Elsevier Ltd. doi:10.1016/j.jenvrad.2003.11.001 48 A.E. Khater et al. / J. Environ. Radioactivity 75 (2004) 47–57 material for all phosphate products. The concentration of 238U and its decay products tend to be elevated in phosphate deposits of sedimentary origin. A comparison of the radiological impacts associated with the phosphate industry with those of uranium mining and milling indicates that most impacts are within one order of magnitude of each other per unit uranium production (Othman et al., 1992). A typical concentration of 238U in sedimentary phosphate deposits is 121 mg kg1 (1500 Bq/ kg) with a range of 30–260 mg kg1 (372–3224 Bq/kg) (UNSCEAR, 1993; Altschuler, 1980). The uranium contents of some Egyptian phosphate rocks in the Red Sea coast and several Nile valley sites are in the ranges of 19–142 mg kg1 (235–1761 Bq/ kg) and 48–185 mg kg1 (595–2294 Bq/kg), respectively (Bigu et al., 2000). The average 238U content in Abu-Tartor phosphate rock is about 32.9 mg kg1 (408 Bq/kg) (Khater et al., 2001). The primary potential environmental radiation problem is associated with phosphate rock mining and processing concerns, mining spoils and processing waste products. Occupational exposures mainly occur during mining process and transportation of phosphate rock, as well as during transportation and utilization of phosphate fertilizers. It has been indicated that 222Rn gas (a decay product of 238 U–226Ra series) and its progeny constitute the largest single contributors to human radiation exposure from natural and man-made radioactive sources (UNSCEAR, 1988, 1977). Inhalation of radon and its short-lived decay products constitutes the most important occupational exposure of workers in mines (Amer et al., 2002). It is obvious that extraction of phosphate ore presents potential health hazards in addition to its chemical toxicity, particularly when the ore requires building subterranean facilities, i.e. underground mines, for its extraction. The problem is a consequence of poor or inadequate air ventilation which has a close relationship to 222 Rn concentration in the underground mine tunnels (Altschuler, 1980; Bigu et al., 2000). The increased incidence of lung cancer in uranium miners and fluorspars miners due to radon daughters’ concentrations in an underground miner has been documented (Boothe, 1977). Radiation monitoring of workers engaged in phosphate mining and processing activities is essential. In spite of the fact that monitoring itself does not improve working conditions, but demonstrates if operational radiation protection measures function as intended, or whether further protection measures should be considered (Othman et al., 1992). A number of studies have been made to evaluate the occupational exposure in uranium, phosphate, and coal mines (Bigu et al., 2000; Kenawy et al., 1999, Hussein et al., 1997; Amer et al., 2002). Our work aims at the evaluation of the occupational radiation exposure in Abu-Tartor phosphate mine through airborne radioactivity measurements and, assessment of environmental and personal radiation dose rate. Since the mine is still in the experimental operation stage, the results of this work are preliminary. The present work has been conducted under the national program for radiation safety and control of the Egyptian Atomic Energy Authority. 2. Experimental work This study reports the occupational radiation doses received by the workers in Abu-Tartor phosphate mine. Occupational exposures arise from conventional A.E. Khater et al. / J. Environ. Radioactivity 75 (2004) 47–57 49 mining activities. Abu-Tartor mine is a close cast underground mine. The current reserve estimate in the exhaustively investigated area is in the order of a billion tons of phosphate ore (Said, 1990). The planned annual production is 4 million tons of ore rock and 2.2 million tons of wet rock. The ore rock are crushed, sieved, and transported to beneficiation plant to produce the wet rock. The wet rocks are stocked in large open piles for sale or transport to a phosphate chemical plant (Khater et al., 2001). The chart plan of the mine site and ore processing activities are shown in Fig. 1. There are two mechanical ventilation stations, one for the east side and another one for the west side. Auxiliary air pumps are used for ventilation of the side tunnels during build up of the side tunnels and long wall retreats (ore rock cutting). During sampling, the west side ventilation station was not in operation. As a safety procedure, temperature, humidity and air flow rate in the working places inside the mine tunnels are measured and recorded on a routine basis. v Average ranges from 18 to 46 (36.6) C temperatures, from 18 to 56 (39.5)% 3 humidity, and 7–21 (15) m /s air flow rates were recorded during sampling (personal communication). Two types of measurements were carried out in this work: airborne radioactivity measurements (222Rn, 222Rn daughters, and 220Rn), and area and personal gamma dose rate (mSv/y) measurements. Airborne radioactivity measurements were carried out in 20 locations along the mine tunnels, Fig. 2. Radon gas concentration measurements were conducted by the scintillation cell method (Lucas method) (Lucas, 1957). The air sample was sucked into an alpha scintillation chamber. The scintillation chamber, of 160-ml capacity, has inside walls coated with silver activated zinc sulphide, which emit light flashes when struck by alpha particles. The scintillations emitted are measured by placing the transparent surface of the chamber in contact with a photo-cathode detector in a light tight enclosure. Alpha particle count (radioactive gas and decay products) was done using an alpha particle Fig. 1. Chart plan of the mine site and ore processing. 50 A.E. Khater et al. / J. Environ. Radioactivity 75 (2004) 47–57 Fig. 2. Sampling locations for airborne radioactivity measurement in the mine tunnels. counter/scalar; model RDR-511, manufactured by EDA Instruments (Toronto, Canada). A sensitivity of 0.19–0.37 Bq/l (5–10 pCi/l) is attainable with a short counting period. The radon concentration is evaluated by dividing the counts due to alpha particles over the cell factor, which is determined using standard radon gas source. The standard radon gas source is composed mainly of a standard solid radium slat source model Pylon-150 developed by Pylon Electronic Development (Ottawa, Canada), traceable to the National Institute of Standards and Technology (NIST, USA). The estimated cell factor usually ranges from 1.6 to 1.8. Radon (222Rn) progeny concentrations were measured using the Rolle method (Rolle, 1972). Air samples were collected for 5 min at a flow rate about 6 l min1 on high efficiency filter paper (Millipore, diameter 2.5 cm), followed by alpha counting after a delay time of about 5 min. The period of delay was selected to minimize the error resulting from variations in radon daughter ratios. The filter papers were counted using an EDA (RDA-200 Radon Daughter detector, EDA Instrument Inc.) type counting system by placing the filter paper on a scintillation tray coated with silver-activated zinc sulphide. A Pylon RN-190 radon progeny standard source was used for calibration to determine the counting efficiency calibration of the scintillation tray. It houses a dry 226Ra source, which emanates radon gas into a sealed chamber. Radon decays into its daughters, which deposit on the inner surface of the chamber and on an enclosed filter paper. The RN-190 is designed so that the radon progeny are deposited uniformly over the filter and the chamber surface with an activity deposition of 73:16 Bq cm2 4%. For 4 min A.E. Khater et al. / J. Environ. Radioactivity 75 (2004) 47–57 51 counting time measurement, a radon progeny of 0.03 WL (working level) can be measured with a reproducibility of 15%. The radon progeny concentration, expressed as WL, was calculated using the following equation: WL ¼ R=EvtF ð1Þ where R is the alpha count rate in count min1 , E is the counting efficiency, v is the volumetric sampling rate in l min1 , t is the sampling time in min, and F is a conversion factor, which may be approximated by 212 for sampling periods of 1–20 min. One working level represents any combination of short-lived radon daughters’ concentration in 1 l of air that results in the ultimate emission of 1:3 105 MeV of alpha energy, taking no account of the radon (Amer et al., 2002). Thoron (220Rn) progeny concentrations were measured using Rock method (Rock, 1975). Thoron progeny was collected on a high efficiency membrane filter paper for 5 min at a flow rate of about 6 l min1 , followed by alpha counting of the filter after a delay of 5 h or more after the end of sampling. The 212Pb (ThB), a beta emitter, is in transient equilibrium with its alpha-emitting daughters, enabling its air concentration at the time of sampling to be calculated readily from the alpha count. A minimum detectable activity of 0.02 Bq/l is obtained using such technique. Thoron was calculated using the following equation: CThB ¼ 0:411Re0:001086T =Evt ð2Þ where CThB is the ThB concentration, R is the count rate at T min from the end of sampling (count min1 ), T is the interval from the end of sampling until counting (>300 min) in min, E is the counting efficiency, v is the volumetric sampling rate in l min1 and t is the sampling time in minutes. Forty locations and 45 workers were chosen to carry out area and personal effective dose measurements using TLD, respectively. The TLD Dosimeters for area monitoring of the mine tunnels were hung in the middle of the tunnels. The 45 workers were provided with TLD Dosimeters. They wore the dosimeter on the part of the body between their neck and waist that was most likely to be exposed to the greatest amount of radiation. The dosimeter assemblies consist of two parts, a TLD card and a holder. The TLD card consists of four hot-pressed LiF-100 (LiF:Mg,Ti) TL chips of 3 3 0:38 mm3 encapsulated between two sheets of Teflon 10 mg/cm2 thick and mounted on an aluminium substrate. The holder is made of durable, tissue-equivalent, ABS plastic, and is sealed to retain the card in a light and moisture excluding environment. It also protects the card from environmental damage and retains the filtration media. A Harshaw 6600 reader was used. 3. Results and discussion 3.1. Airborne radioactivity measurements The results of airborne radioactivity measurements in Abu-Tartor phosphate mine are shown in Table 1. The average standard deviation (range) values of 222 Rn (Bq/m3), 222Rn daughters (WL, mSv/y) and 220Rn (Bq/m3) in Abu-Tartor, 52 A.E. Khater et al. / J. Environ. Radioactivity 75 (2004) 47–57 Table 1 Activity concentrations of radon gas (222Rn) and thoron gas (220Rn) in Bq/m3, and radon daughter products (222Rn daughters) estimated in level unit (WL) and annual effective dose (mSv/y) in Abu-Tartor phosphate mine Serial no. Sample code Distance (m)a Distance (m)b 222 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 17 18 19 20 451 385 193 0 250 500 800 1000 1200 1400 1600 2148 2532 2632 2672 2723 2865 2905 3206 3232 93 66 40 – – – – – – – – – – 190 51 – 436 463 776 790 4903:0 242 5153:0 248 – – – – – – – – – – – – 1801.3 147 – 3543:0 208 – – 5535.0 258 10 11 12 13 14 15 16 17 18 19 20 6 3 7 2 1 5 4 9 8 Rn (Bq/m3) 222 Rn daughters 220 Rn (Bq/m3) c WL mSv/y 0.25 0.67 0.52 0.14 0.10 0.08 0.07 0.06 0.07 0.06 0.04 0.17 0.03 0.23 0.10 0.01 0.42 0.45 0.43 0.60 30.46 80.99 63.00 16.34 11.65 10.10 7.86 7.20 7.93 7.28 4.63 20.99 3.12 27.80 11.61 0.69 50.22 53.52 51.53 71.56 3.40 16.37 9.05 5.17d – – – – – – – 1.98 1.00 5.74d 1.66d – 5.15d – 13.15 8.81d Minimum and maximum values are italicized. a Distance from mechanical ventilation station. b Distance from the side tunnel entrance. c C:F: ¼ 62:5 lSv h1 =WL. d Natural ventilation. Red Sea phosphate mines, El-Missikat uranium mine, and Erediya uranium mine are given in Table 2. The 222Rn concentrations in Bq/m3 were measured in five locations in the side tunnels. All measurements are exceeding the limits for occupational exposure to radon (1000 Bq/m3) (IAEA, 1996). The mean 222Rn concentration standard error (SE) is 4187 685 Bq=m3 with a range of 1801–5535 Bq/m3. The mean 222Rn concentration in other Egyptian phosphate mines is 5772 Bq/m3 where some of these mines depend on the natural ventilation as in the west side of AbuTartor mine during our field measurements (Bigu et al., 2000). The mean conce ntration SE (range) of 222Rn decay products in working level unit and its effective annual dose rate in mSv/y are 0:22 0:05 (0.01–0.67) and 26:90 5:67 (0.69–80.99), respectively. The annual effective dose rate due to 222Rn decay products is exceeding the recommended limit, 20 mSv/y (ICRP-60), especially in the side tunnels locations by a factor of up to 4-fold because of the inadequate and bad ventilation (Bigu et al., 2000; ICRP, 1991). The relationship between the concentration of 222Rn decay products in units of working level and distance A.E. Khater et al. / J. Environ. Radioactivity 75 (2004) 47–57 53 Table 2 The average standard deviation (range) values of 222Rn (Bq/m3), 222Rn daughters (mSv/y and WL) and 220Rn (Bq/m3) in Abu-Tartor phosphate mine and other Egyptian phosphate and uranium mine 222 Rn (Bq/m3) Abu-Tartor phosphate mine Red Sea phosphate mines El Missikat uranium mine Erediya uranium mine 4187 685 (1801–5535) – (1311–12448) – – – – 26:90 5:70 (0.69–81.99) 0:22 0:05 (0.01–0.67) – – – – – – – (1.40–5.60) – – – (2.26–6.22) 6:50 1:48 (1.00–16.40) – – – – – – 222 Rn daughters mSv/y WL 220 Rn (Bq/m3) from the main mechanical ventilation station in the main tunnel, RG3, (sample codes: 13–20) is shown in Fig. 3. This relationship shows clearly the effect of ventilation efficiency on the concentration of 222Rn daughters and subsequently Fig. 3. The concentration of 222Rn daughters (WL) in Abu-Tartor phosphate mine tunnels and the distance from the main ventilation station (A). 54 A.E. Khater et al. / J. Environ. Radioactivity 75 (2004) 47–57 on the other airborne radioactivity and worker radiation exposure. This relation does not fit to the other locations especially in the side tunnels because of the complex layout of the mine and the different ventilation mechanisms. The mean 220 Rn concentration SE was 6:50 1:48 Bq/m3 with a range of 1.00–16.40 Bq/m3. The inhalation hazard of 220Rn daughters is almost entirely dependent on the air concentration of only one radionuclide, 212Pb. The concentrations of 222 Rn (Bq/m3), 222Rn daughters (Bq/m3), and 220Rn in units of Bq/m3 inside the mine tunnels are given in Fig. 4. There is an inverse relationship between the concentration of airborne radioactivity in the mine tunnels and the air ventilation. In the side tunnels, only auxiliary fans were used for air ventilation, which are not enough to control the airborne radioactivity within the recommended limit. For this reason, mechanical ventilation is conventionally used as Fig. 4. Activity concentration of 222Rn (Bq/m3), tance (m) from the ventilation station (A). 222 Rn daughters (WL) and 222 Rn (Bq/m3), and the dis- A.E. Khater et al. / J. Environ. Radioactivity 75 (2004) 47–57 55 an effective way to control airborne radioactivity and other airborne pollutants in the underground mines (Bigu et al., 2000). The correlations between 222Rn and 222Rn daughters, and 220Rn and 222Rn daughter concentrations are given in Fig. 5, with correlation coefficient values of 0.87 and 0.86, respectively. Fig. 5. The correlations between the concentrations of 222Rn (Bq/m3) and 222 Rn daughters and 220Rn (Bq/m3) in Abu-Tartor mine tunnels. 222 Rn daughters (WL), and 56 A.E. Khater et al. / J. Environ. Radioactivity 75 (2004) 47–57 3.2. Dose assessment The environmental and personal effective dose rate (mSv/y) measured using TLD are shown in Table 3. Forty locations in three sites in the mine were selected for environmental gamma dose rate measurements. The mean environmental effective dose rate was 8.97 mSv/y. Forty-five workers in five sites in different mining activity areas were selected. The mean value of the workers effective dose rate was 11.66 mSv/y. The maximum values were measured for the mine tunnel workers. The average total effective dose rate (due to 222Rn, 222Rn progeny, and 220Rn progeny) in other Egyptian phosphate mines was 70.2 mSv/y with a range of 12.2–136.9 mSv/y. The workers response should be considered, which may be affecting the precision of any survey results in radiation safety and control application (Hussein, 1998). 3.3. Conclusion and recommendations The occupational radiation exposure in the underground conventional mines is one of the major aspects in the Egyptian national program of radiation safety and control. This study, in addition to pervious studies in uranium and phosphate underground mines, implies the urgent need to impose the radiation regulations and standards through improving the working conditions to reduce the occupational radiation exposure to the accepted levels recommended by ICRP-60 and IAEA-Safety series 115. In such working condition, it is a necessity to impose a periodical radiation-monitoring program in order to continuously define and assess possible radiological problems and to carry out the proper countermeasures. So, we can summarize our conclusion in the following prevention and remedialmeasures and recommendations: efficient ventilation is a must. Job rotation of Table 3 Environmental and personal effective dose rate (mSv/y) measured in Abu-Tartor phosphate mine tunnels using TLD Worker effective dose rate (mSv/y) Mine worker Mine maintenance worker Ore crushing and transport workers Beneficiation factory workers Ore drying and storage workers Average Mean SE SD Minimum Maximum No.a 15.55 10.25 11.34 10.95 10.21 11.66 2.73 0.97 1.03 0.35 0.15 – 12.20 3.64 1.78 0.79 0.26 – 6.78 5.90 9.83 10.09 9.97 6.78 53.52 18.23 13.31 12.11 10.49 53.52 20 14 3 5 3 – 0.60 0.31 0.52 – 3.36 0.70 1.08 – 2.19 8.94 6.82 2.19 17.09 10.81 9.07 17.07 31 5 4 – Environmental gamma effective dose rate (mSv/y) Mine 8.51 Ore crushing 10.06 Beneficiation factory 8.35 Average 8.97 SE, Standard error (1 r); SD, standard deviation. a Number of measurements. A.E. Khater et al. / J. Environ. Radioactivity 75 (2004) 47–57 57 workers is very important to decrease occupational radiation dose. Radiological safety should be considered in conventional mines. Regulations should be issued and applied by the administration of these sites. Radiological follow up should be a routine. Medical follow up system should be applied. Acknowledgements Authors wish to express their deep gratitude to Abu-Tartor phosphate mine project authority and Mr. Walid El-Moafy for their assessment and support during field measurement activities. References Altschuler, Z.S., 1980. The geochemistry of trace element in marine phosphorites. Soc. Econ. Paleontologists Mineralogist Spc. Pub. 29, 19–30. Amer, A.H., Shawky, S., Hussein, M.I., Abd El-Hady, M.L., 2002. Radiological study of exposure levels in El Maghara underground coal mine. J. Environ. Monit. 4, 583–587. Bigu, J., Hussein, M.I., Hussein, A.Z., 2000. Radioactivity measurements in Egyptian phosphate mines and their significance in the occupational exposure of mine workers. J. Environ. Radioact. 47, 229–243. Boothe, G.F., 1977. The need for radiation controls in the phosphate and related industries. Health Phys. 32, 285–290. Hussein, A.Z., Hussein, M.I., Huwait, M., 1997. On the study of some engineering problems related to airborne radioactivity in underground phosphate mines. In: Al-Azhar Engineering Fifth International Conference, December 19–22, Cairo, Egypt. Hussein, M.I., 1998. Human error in radiation safety applications. New Egyptian J. Med. 11, 45–46. International Atomic Energy Agency, 1996. Safety standard series no. 115. International Commission on Radiological Protection, 1991. Publication no. 60. Oxford: Pergamon Press. Kenawy, M.A., Sayyah, T.A., Hussein, M.I., Morsy, A.A., Said, A.F., 1999. Detailed study of radiation exposure problem in uranium underground sites in Egypt. Al-Azhar Bulletin of Science. Khater, A.E.M., Higgy, R., Pimpl, M., 2001. Radiological impacts of natural radioactivities in Abu-Tartor phosphate deposit, Egypt. J. Environ. Radioact. 55, 255–267. Lucas, H.F., 1957. Improved low level alpha scintillation counter for radon. Rev. Sci. Instrum. 28, 680– 683. Othman, I., Al-Hushari, M., Raja, G., 1992. Radiation level in phosphate mining activities. Radiat. Prot. Dosimet. 45 (1/4), 197–201. Rock, R.I., 1975. Sampling mine atmospheres for potential alpha energy due to the presence of radon220 (Thoron) daughters. MESA Information Report IR-1015. Washington, DC, USA: US Dept. of the Interior. Rolle, R., 1972. Rapid working level monitoring. Health Phys. 22, 233–238. Said, R., 1990. Geology of Egypt. A.A. Balkema/Brookfield, Rotterdam. Santo, P.L., Gouvea, R.C., Dutra, I.R., 1995. Human occupational radioactive contamination from the use of phosphated fertilizers. Sci. Total Environ. 162, 19–22. UNSCEAR, 1977. Sources and effects of ionizing radiation. United Nations Scientific Committee on the Effects of Atomic Radiation. Report to General Assembly, United Nations, New York. UNSCEAR, 1988. Sources and effects of ionizing radiation. United Nations Scientific Committee on the Effects of Atomic Radiation. Report to General Assembly, United Nations, New York. UNSCEAR, 1993. Sources and Effects of Ionizing Radiation. United Nations Scientific Committee on the Effects of Atomic Radiation. Report to General Assembly, United Nations, New York. International Congress Series 1276 (2005) 407 – 408 www.ics-elsevier.com Natural radioactivity contents in tobacco N. Abd El-Aziza, A.E.M. Khatera,*, H.A. Al-Sewaidanb a b National Center for Nuclear Safety and Radiation Control, Atomic Energy Authority, Cairo, Egypt Physics Department, College of Science, King Saud University, Riyadh, Kingdom of Saudi Arabia, P.O. Box 7551, Nasr City, Cairo, Egypt Abstract. Tobacco contains minute quantities of radioactive isotopes of uranium series and thorium series (210Pb, 210Po and 226Ra), which are radioactive carcinogenic. Smoking of tobacco and its products increases the internal intake and radiation dose due to natural radionuclides. In a number of studies, inhalation of some naturally occurring radionuclides via smoking has been considered to be one of the most significant causes of lung cancer. In this work, Moasel tobacco samples were collected from the Saudi and Egypt markets. Natural radionuclides (234Th, 226Ra, 210Pb, 214Bi, 228Ac, 40K and 210 Po) in tobacco were measured using g-ray spectrometer and a spectrometer. The measured data were presented and discussed. D 2004 Published by Elsevier B.V. Keywords: Tobacco; Moasel; Natural radioactivity; Polonium; Smoking 1. Introduction Tobacco contains minute quantities of radioactive isotopes such as uranium series and thorium series isotopes (210Pb, 210Po and 226Ra), that are radioactive carcinogenic and could be found in smoke from burning tobacco. People who intentionally or passively inhale tobacco smoke are exposed to higher concentrations of radioactivity than nonsmokers. Deposits of radioactive isotopes in the lungs of smokers, delivered to sensitive tissues for long periods of time, generating localized radiation exposures, may induce cancer both alone and synergistically with non-radioactive carcinogens. In a number of studies, inhalation of some naturally occurring radionuclides via smoking has been considered to be one of the most significant causes of lung cancer [1]. Jurak and Moasel tobacco products, smoked using hubble-bubble (water-pipe), are popular in the Middle Eastern and North African countries. It is unlike smoking cigarettes, where the filter * Corresponding author. Present address: Physics Department, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Kingdom of Saudi Arabia. Tel.: +966 50 241 8292; fax: +9661 46 76 448. E-mail address: [email protected] (A.E.M. Khater). 0531-5131/ D 2004 Published by Elsevier B.V. doi:10.1016/j.ics.2004.11.166 408 N. Abd El-Aziz et al. / International Congress Series 1276 (2005) 407–408 Table 1 Specific activity of Th-234, Ra-226, Pb-210, Ac-228 and K-40 (Bq/kg dry weight) in different types of Moasel tobacco Th-234 Ra-226 Pb-210 Bi-214 Ac-228 K-40 Po-210 No. of samples Type K Type S Type Z Average 8.80F1.40, 3.43*(5.41–13.24) 7.54F0.89, 2.37 (3.60–9.85) 16.42F2.21, 6.98 (5.14–25.7) 2.42F0.42, 1.19 (1.17–4.28) 6.49F1.0, 2.91 (1.6–10.28) 617.0F28.1, 88.9 (474.6–725.8) 10.55F2.13, 3.69 (6.67–14.02) 10 9.38F1.44, 3.22 (5.56–12.32) 6.32F0.76, 2.15 (4.43–9.31) 14.44F1.34, 4.24 (10.27–22.2) 2.00F0.40, 0.69 (1.20–2.40) 0.82F0.21 5.69F0.28 795.9F38.7, 116.0 (701.0–1043.0) 15.02F5.65, 11.30 (6.94–31.75) 10 607.9F50.2, 100.3 (511.9–747.0) – 8.76F0.92, 3.18 (5.41–13.24) [12]** 6.98F0.56, 2.3 (3.6–10.14) [17] 15.62F1.21, 5.94 (5.14–25.67) [24] 2.02F0.26, 1.02 (1.15–4.28) [15] 5.78F1.19, 3.36 (0.82–10.28) [8] 685.4F27.8, 133.1 (568.7–1043.3) [23] 13.10F3.25 (6.67–31.75) [7] 4 24 7.68F2.46, 3.48 (5.22–10.14) 16.59F3.96, 7.91 (5.49–22.92) 1.25F0.04, 0.07 (1.15–1.30) – * MeanFstandard error, standard deviation (range); ** Number of data. removes a minimum of 96% of the particulate phase of smoke [1]. This study aimed at assessment of radioactivity content in Moasel tobacco products to provide the necessary data to estimate the possible health effects of tobacco smoking. 2. Experimental techniques Three most frequently smoked brands of Moasel tobacco were chosen. Samples were collected randomly from those available on the Saudi and Egypt markets. Samples were dried, pulverized, homogenized and transferred to polyethylene containers of 100-cm3 capacity. Gamma-ray spectrometry: 234Th, 226Ra, 210Pb and 214Bi (238U series), 228Ac (232Th series), and 40K were measured using calibrated gamma-ray spectrometer; based on Hyper Pure Germanium detector with efficiency of 40% and full width at half maximum (FWHM) of 1.95 keV for 60Co g-line at 1332 keV[2]. 210Pb-210Po analysis: Polonium-210 was measured after chemical separation and plating on stainless steel disk using alpha spectrometers (CANBERRA, Mod. 7401 VR) based on passivated implanted planar silicon (PIPS) [3]. 3. Results and discussion Specific activity (Bq/kg) of 234Th, 226Ra, 210Pb, 214Bi, 228Ac, 40K and 210Po in 3 Moasel tobacco types and their averages are given in Table 1. Abdul-Majid (1995) reported that the average specific activity of 226Ra, 223Th and 40K in Egyptian’s Moasel tobacco were 2.1, 2.8 and 471 Bq/kg, which is lower than our results. Estimation of internal dose due to inhalation of 234Th, 226Ra, 210Pb, 214Bi, 228Ac, 40K and 210Po via Moasel tobacco smoking will be performed in the near future work because several parameters are required, e.g. particulate size distribution, inhalation pattern, particle aerodynamics and the distribution factors of these radionuclides between smoke, ash and cooling water of hubble-bubble [1]. References [1] S. Abdul-Majid, I.I. Kutbi, M. Basabrain, J. Radioanal. Nucl. Chem., Artic. 194 (2) (1995) 371 – 377. [2] M. El-Tahawy, et al., J. Nucl. Sci. 29 (1992) 361 – 363. [3] A.J. Khater, Environ. Radioact. 71 (2004) 33 – 41. Egyptian Atomic Energy Authority National Center for Nuclear Safety and Radiation Control PROCEDURES MANUAL RADIOCHEMICAL ANALYSIS OF CERTAIN NATURALLY OCCURING AND MAN-MADE RADIONUCLIDES IN ENVIRONMENTAL SAMPLES Edited by Randa H. Higgy, Ashraf E.M. Khater & M. Pimpl 2003 2 Contents Page 1- Abstract : 6 2-Naturally Occurring radionuclides: 7 2-1 Determination of Uranium isotopes 7 2-1-1 Introduction 7 2-1-2 Principle of the analytical procedure 7 2-1-3 Sample preparation 7 2-1-3-1 Soil and sediment samples 7 2-1-3-2 Biological Sample materials 8 2-1-3-3 Plants 8 2-1-3-4 Milk 9 2-1-3-5 Meat and fish 9 2-1-4 Determination 10 2-1-5 Calculation of the results 12 2-1-5-1 Calculation of the chemical yield 12 2-1-5-2 Calculation of uranium isotopes specific activities in the sample 2-1-5-3 Calculation of standard deviation 13 14 2-1-5-4 Calculation of the lower limit of detection 14 2-1-5-5 Calculation of the limit of decision 15 2-1-6 Quality control 15 2-1-7 References 16 2-2 Determination of Thorium isotopes 17 2-2-1 Introduction 17 2-2-2 Principle of the analytical procedure 17 2-2-3 Sample preparation 17 2-2-3-1 Soil and sediment samples 17 2-2-3-2 Biological Sample materials 18 2-2-3-3 Plants 18 3 2-2-3-4 Milk 19 2-2-3-5 Meat and fish 19 2-2-4 Determination 21 2-2-5 Calculation of the results 22 2-2-5-1 Calculation of the chemical yield 22 2-2-5-2 Calculation of uranium isotopes specific activities in the sample 2-2-5-3 Calculation of standard deviation 23 23 2-2-5-4 Calculation of the lower limit of detection 24 2-2-5-5 Calculation of the limit of decision 25 2-2-6 Quality control 25 2-2-7 References 26 2-3 Determination of Lead-210 27 2-3-1 Introduction 27 2-3-2 Principle of the analytical procedure 27 2-3-3 Sample preparation 27 2-3-3-1 Soil and sediment samples 27 2-3-3-2 Biological Sample materials 28 2-3-3-3 Plants 28 2-3-3-4 Milk 28 2-3-3-5 Meat and fish 29 2-3-4 Determination 31 2-3-5 Calculation of the results 32 2-3-5-1 Calculation of the chemical yield 32 2-3-5-2 Calculation of uranium isotopes specific activities in the sample 2-3-5-3 Calculation of standard deviation 32 33 2-3-5-4 Calculation of the lower limit of detection 33 2-3-6 Quality control 33 2-3-7 References 34 2-4 Determination of Polonium-210 2-4-1 Introduction 35 35 4 2-4-2 Principle of the analytical procedure 35 2-4-3 Sample preparation 35 2-4-3-1 Soil and sediment samples 35 2-4-3-2 Biological Sample materials 36 2-4-3-3 Plants 36 2-4-3-4 Milk 36 2-4-3-5 Meat and fish 36 2-4-4 Determination 37 2-4-5 Calculation of the results 38 2-4-5-1 Calculation of the chemical yield 38 2-4-5-2 Calculation of uranium isotopes specific activities in the sample 2-4-5-3 Calculation of standard deviation 38 38 2-4-5-4 Calculation of the lower limit of detection 39 2-4-6 Quality control 39 2-4-7 References 40 3-Man-Made radionuclides; 3-1 Determination of Plutonium isotopes 41 41 3-1-1 Introduction 41 3-1-2 Principle of the analytical procedure 41 3-1-3 Sample preparation 42 3-1-3-1 Soil and sediment samples 42 3-1-3-2 Biological Sample materials 43 3-1-3-3 Plants 43 3-1-3-4 Milk 43 3-1-3-5 Meat and fish 43 3-1-4 Determination 46 3-1-5 Calculation of the results 47 3-1-5-1 Calculation of the chemical yield 47 3-1-5-2 Calculation of uranium isotopes specific activities in the sample 3-1-5-3 Calculation of standard deviation 48 48 5 3-1-5-4 Calculation of the lower limit of detection 49 3-1-5-6 Calculation of the limit of decision 50 3-1-6 Quality control 50 3-1-7 References 51 6 1- ABSTRACT: The aim of the present report is to provide a detailed description of the radiochemical procedures for the determination of some radionuclides in the environmental samples, which are routinely analyzed in the Central Laboratory for Environmental Radiation Measurement (CLERMIT) – National Center for Nuclear Safety and Radiation Control, Egyptian Atomic Energy Authority. This procedures manual is an essential part of the laboratory quality control documents, which should be followed to perform any routine analysis in the CLERMIT. The principle scheme for radiochemical separation and analysis of radionuclides in the environmental samples are start with the addition of the suitable radioactive tracers or stable carriers, sample dissolution, radionuclides separation and purification, source preparation and measurement and, finally, activity concentration and uncertainty calculations. The calculations of activity concentration, uncertainties, and lower limits of detection for the analyzed radionuclides are given in details. Other radionuclides such as Strontium-90, Americium-241 and Radium-226 are not analyzed routinely using radiochemical separation in our laboratory. It is planned to include these radionuclides in the procedures manual in the near future. 7 2- Naturally Occurring radionuclides 2-1 DETERMINATON OF URANIUM ISOT OPES 2-1-1 INTRODUCTION Natural uranium can be detected in low concentrations in nearly all materials from the environment. Uranium is the fuel for about 1000 nuclear reactors of various kinds that exist in the world. These reactors produce electricity, produce plutonium for nuclear and thermonuclear weapons, and serve the search need of physical and biological scientists. In addition to the natural uranium, uranium is discharged into the environment due to mining activities, using special military weapons and liquid and gaseous effluents from nuclear facilities. In the radiochemical equilibrium, it consists of the isotopes 234 U, 235 U and 238 U with the natural activity ratio of 1:0.0462:1, corresponding to a mass ratio of 0.0054: 0.711:99.2836 percent. All of these three nuclides are alpha-emitters. From nuclear facilities, additional amounts of uranium are discharged into the environment. In effluents from nuclear facilities, the ratios of uranium isotopes differ very much. To be able to compare them with that from natural background, it is necessary to determine not only the concentration of total uranium but also the ratio of the different uranium isotopes. 2-1-2 PRINCIPLE OF THE ANALYTICAL PROCEDURE: The ashed sample is spiked with uranium tracer (232U) for chemical yield and activity calculation. The ashed sample is dissolved using HNO3, HCl and HF acids. Uranium in the dissolved sample solution is extracted from most of the matrix elements with TOPO (Trioctylphosphine oxide) and backextracted with 1M NH4F/0.1 M HCl solution. The uranium fraction is purified by coprecipitation with LaF3 and anion exchange. Finally, the pure uranium fraction is electrodeposited on a stainless steel disk from HCl/oxalate solution and measured by mean of alpha spectrometry. 2-1-3 SAMPLE PREPARATION: 2-1-3-1 Soil and Sediment Samples 1. Dry the sample at 110 0C until the weight remains constant, then ground, homogenize and sieve the dried sample through a 2 mm sieve. 2. Weigh about 10 g of dried sample and moisture it with HNO3 till no further reaction occurs. Dry the sample on a sand bath. 8 3. Ash the dried sample at 550 0C at least for 6-8 hours. Ground and homogenize the sample ash. Note (A): If the residue is not free of organic carbon, which can be recognized by a dark brown or black coloured ash, then repeat the ashing process again. 4. Weigh up to 5 g ashed sample into a Pt- or Teflon dish and add 232 U tracer (50-100mBq) for chemical yield determination. 5. Add 40 ml HNO3 and 10 ml HF, and digest on a medium temperature (70-800C) hot plate. 6. Repeat step (5) until no further dissolution takes place (white residue). 7. Add 3 ml HNO3 (65%) for three times and evaporate to near dryness. 8. Dissolve the sample residue in 100 ml 8 M HNO3 in a 250 ml glass beaker and cover it with a watch glass. 9. Boil the sample solution for 30 min., cool it to room temperature and adjust the solution volume to 100 ml 10. Continue with determination. 2-1-3-2. Biological Sample Materials (plants, milk, meat and fish) 2-1-3-2-1 Plants: 1. Dry the sample at 110 0C until the weight remains constant, then ground and homogenize the dried sample. 2. Ash the dried sample material at 550 0C at least for 6-8 hours. Ground and homogenize the sample ash (see Note A) . 3. Weigh up to 20 g of ashed sample material into an Erlenmeyer flask (1 L) and add 232 U tracer (50-100 mBq) for chemical yield determination. 4. Add 100 ml of HNO3 and digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 5. Repeat the addition of HNO3 and digestion till you have a clear solution. 6. Evaporate the solution to near dryness and dissolve the sample residue in 100 ml 8M HNO3 in a 250 ml glass beaker and cover it with a watch glass. 7. Boil the sample solution for 30 min., cool it to room temperature and adjust the solution volume to 100 ml 9 8. Continue with determination. 2-1-3-2-2 Milk: 1. Dry up to 3 l of milk under an infrared lamp in a porcelain dish. 2. Cover the samples with HNO3 (65%) and add 232U tracer (50-100 mBq) for chemical yield determination. 3. Digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 4. Repeat the addition of HNO3 and digestion till you have a clear solution. 5. Evaporate the solution to near dryness and ash the residue at 550 0C for 6-8 hours (see Note A). 6. Dissolve the sample residue in 100 ml 8M HNO3 in a 250 ml glass beaker and cover it with a watch glass. 7. Boil the sample solution for 30 min., cool it to room temperature and adjust the solution volume to 100 ml 8. Continue with determination. 2-1-3-2-3 Meat and fish: 1. Cut up to 100 g of the sample to small pieces and transfer it into a 2 l beaker. 2. Cover the samples with HNO3 (65%) and add 232U tracer (50-100 mBq) for chemical yield determination. 3. Digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 4. Repeat the addition of HNO3 and digestion till you have a clear solution. 5. Evaporate the solution to near dryness and ash the residue at 550 0C for 6-8 hours (see Note A). 6. Dissolve the sample residue in 100 ml 8M HNO3 in a 250 ml glass beaker and cover it with a watch glass. 7. Boil the sample solution for 30 min., cool it to room temperature and adjust the solution volume to 100 ml 8. Continue with determination. 10 Schematic Representation of the Radiochemical Procedure of Uranium Ashed Samples Material add yield tracer U-232 Digestion with HNO3,HCl and HF Dissolved Sample Material Extraction with TOPO/Cyclohexane Aqueous Phase : discard Organic Phase: wash 3 times with 3 M HCl Backextraction with NH4F/HCL Organic Phase: discard Aqueous Phase: wash 3 times with CHCl3 add TiCl3, La(NO3)3, HF Coprecipitation with LaF3 wash precipitation with 1.5 M HF dissolve in H3BO3 (saturated)/HNO3 (65%) add H2O2 (30%) evaporate to dryness dissolve in 9 M HCl Anion-Exchange Dowex 1x2, 50 - 100 mesh Cl- form wash with 9 M HCl elute with 1M HNO3 evaporate to dryness dissolve with 4 M HCl add (NH4)2C2O4 (4%) Electrodeposition Alpha-Spectrometry 11 2-1-4 DETERMINATION: 1. Transfer the dissolved sample into a 250 ml separation funnel. 2. Extract uranium isotopes with 25 ml 0.2 M TOPO/Cyclohexane by shaking for 15 min each. 3. After phase separation, transfer the organic phase into another 250 ml separation funnel. 4. Extract again uranium isotopes with 25 ml 0.2 M TOPO/Cyclohexane by shaking for 15 min each. Combine the organic phases in the 250 ml separation funnel. Discard the aqueous phase. 5. Wash the organic phase three times with 50 ml 3 M HCl by shaking for 5 minutes each. Discard the washing solutions. 6. Backextract uranium isotopes two times with 25 ml 1 M NH4F / 0.1 M HCl by shaking for 15 min each. Combine the aqueous phases and discard the organic phase. 7. Wash the aqueous phase two times with 50 ml CHCl3 by shaking for 2 min each. Discard the organic phases. 8. Transfer the solution into a 100 ml polyethylene centrifuge tube. Add dropwise 2-3 ml of TiCl3 (15%) until you have a violet colour. The colour should stay visible for 10 minutes. 9. Add 20 ml HF (40%) and 2 ml La(NO3)3 (25 mg La3+/ml). After a short interval of agitation, centrifuge the sample solution for 5 minutes at 3000 rpm to separate the fine crystalline precipitate. 10. Repeat the addition of two times 2 ml La(NO3)3 (25 mg La3+/ml) each, centrifuge the sample solution for 5 minutes at 3000 rpm then discard the aqueous phase after decanting. 11. Wash the precipitate carefully with 15 ml 1.5 M HF and centrifuge the sample solution for 5 min at 3000 rpm. Discard the aqueous phase after decanting. 12. Dissolve the precipitate in 10 ml hot saturated HBO3 and 10 ml concentrated HNO3. 13. Add 1 ml H2O2 (30%) and leave the sample solution for 15 minutes. 14. Evaporate the sample solution to dryness. 15. Dissolve the sample residue in 10 ml 9 M HCl by heating for a while. Cool the sample solution to room temperature. 12 Column Preparation: Transfer about 1 g Dowex (1 x 2, 50-100 mesh, Cl-form) with distilled water into a glass column of 15 cm length with inner diameter of 8mm. Condition the column by passing 50 ml 9 M HCl at a rate of 1 ml/min. 16. Pass the sample through the conditioned anion exchanger column at a rate of 1ml/min. 17. Wash the column with 50 ml 9 M HCl at a rate of 1 ml/min. Discard the washing solutions. 18. Elute uranium isotopes with 50 ml 1 M HNO3 in a crystallizing dish. 19. Evaporate to dryness. Add twice 1 ml HCl (32%) and fume to dryness each time. 20. Rinse carefully the crystallizing dish with 0.4 ml 4 M HCl and transfer the solution into a cleaned electrolytic cell for electrodeposition on a stainless steel plate. 21. Rinse the crystallizing dish again three times with 1 ml (NH4)2C2O4, 4 %, each and transfer the solutions into the cell. 22. Rinse the crystallizing dish again with 0.6 ml distilled H2O and transfers the solution into the cell. 23. Perform electrodeposition for 3 hours with 300 mA. 24. Before switching off the current, add 1 ml NH3, 25 %, and continue the electrolysis for 1 min. 25. Discard the solution, then rinse the cell with distilled H2O, discard the water and then disconnect the current. 26. Remove the stainless steel disk out of the cell and rinse it with distilled H2O and then ethanol. 27. Measure the alpha activity on the stainless steel disk by mean of alpha spectrometry. 2-1-5 Calculation of the Results 2-1-5-1 Calculation of the Chemical Yield η= where: η Cn,U-232 CEx,U-232 C n ,U − 232 C Ex ,U − 232 ⋅ 100 chemical yield, in % measured net count rate in the U-232-Peak, in s-1 expected count rate in the U-232-Peak, in s-1 13 C Ex ,U − 232 = AU − 232 ⋅ t M ⋅ ε AU-232 tM ε added U-232-activity, in Bq time of measurement of the sample, in s counting efficiency of the measuring device 2-1-5-2 Calculation of uranium isotopes specific activities in the sample; The activities are calculated as it is done commonly for isotope dilution analysis: AU − 238 = AU − 232 ⋅ [CU − 238 − C 0,U − 238 − CT ,U − 238 ] M ⋅ (CU − 232 − C 0,U − 232 ) AU − 235 = AU − 232 ⋅ [CU − 235 − C 0,U − 235 − CT ,U − 235 ] ρ U − 235 ⋅ M ⋅ (CU − 232 − C 0,U − 232 ) AU − 234 = AU − 232 ⋅ [CU − 234 − C 0,U − 234 − CT ,U − 234 ] M ⋅ (CU − 232 − C 0,U − 232 ) where: AU-238 AU-235 AU-234 M CU-238 C0,U-238 CU-235 C0,U-235 CU-234 C0,U-234 CU-232 C0,U-232 CT,U-238 CT,U-235 CT,U-234 AU-232 ρU-235 specific activity or concentration of U-238, in Bq/g or Bq/l specific activity or concentration of U-235, in Bq/g or Bq/l specific activity or concentration of U-234, in Bq/g or Bq/l amount of sample taken for analysis, in g or l count rate in the U-238-peak, in s-1 background count rate in the U-238-peak, in s-1 count rate in the U-235-peak, in s-1 background count rate in the U-235-peak, in s-1 count rate in the U-234-peak, in s-1 background count rate in the U-234-peak, in s-1 count rate in the U-232-peak, in s-1 background count rate in the U-232-peak, in s-1 background in the U-238-Peak, in s-1 (count rate, which is not produced by the decay of U-238, but is a consequence of peak tailing) background from peak tailing in the U-235-Peak, in s-1 background from peak tailing in the U-234-Peak, in s-1 activity of U-232, added for yield determination, in Bq emission probability for α-decay of U-235 (ρU-235 = 0,816) 14 2-1-5-3 Calculation of the standard deviation; The standard deviations of the uranium activities are obtained with the following equations: 2 s D ,U − 238 AU − 232 CU − 238 C 0,U − 238 CT ,U − 238 C n ,U − 238 CU − 232 C 0,U − 232 ⋅ = ⋅ + + + + C t M ⋅ C n ,U − 232 tM t0 tM t0 , − 232 n U M 2 s D ,U − 235 = s D ,U − 234 ρ U − 235 AU − 232 CU − 235 C 0,U − 235 CT ,U − 235 C n ,U − 235 CU − 232 C 0,U − 232 ⋅ ⋅ + + + + C tM t0 tM t0 ⋅ M ⋅ C n ,U − 232 n ,U − 232 t M AU − 232 CU − 234 C 0,U − 234 C T ,U − 234 C n ,U − 234 = ⋅ + + + M ⋅ C n ,U − 232 tM t0 tM C n ,U − 232 2 CU − 232 C 0,U − 232 ⋅ + t t 0 M where: sD,U-238 sD,U-235 sD,U-234 Cn,U-238 Cn,U-235 Cn,U-234 CU-232 tM t0 standard deviation of the U-238 specific activity or concentration, in Bq/g or Bq/l standard deviation of the U-235 specific activity or concentration, in Bq/g or Bq/l standard deviation of the U-234 specific activity or concentration, in Bq/g or Bq/l net count rate in the U-238-Peak net count rate in the U-235-Peak net count rate in the U-234-Peak net count rate in the U-232-peak time of measurement of the sample, in s time of measurement of the background, in s 2-1-5-4 Calculation of the lower limit of detection (according to German standard DIN 25 482) DU, − 238 = DU, − 235 = ( k1−α + k 1− β ) ⋅ AU − 232 M ⋅ C n,U − 232 ( k1−α + k 1− β ) ⋅ AU − 232 ρ U − 235 ⋅ M ⋅ C n ,U − 232 ⋅ C 0,U − 238 t M ⋅ 1 + tM t0 C T ,U − 238 + tM ⋅ C 0,U − 235 t M ⋅ 1 + tM t0 C T ,U − 235 + tM 15 DU, − 234 = (k 1−α + k1− β ) ⋅ AU − 232 M ⋅ C n ,U − 232 ⋅ C 0,U − 234 t M ⋅ 1 + tM t0 C T ,U − 234 + tM where: k1-α Quantil of the Gaussian distribution for errors of 1st order (pre-select risk for concluding falsely that activity is present) k1-β Quantil of the Gaussian distribution for errors of 2nd order (predetermined degree of confidence for detecting the presence of activity) DIN 25 482-1 recommends for the errors of 1st and 2nd order a probability of 0.05. This means that k1-α = k1-β = 1.645 at the 95 % confidence level. The alpha-spectra of blank samples very often show more counts than background measurements of clean stainless steel plates. This means that the analytical procedure is not able to separate other alpha emitting nuclides completely. To minimize the risk that you falsely conclude that activity is present, it is advisable to pre-select an error probability of 0.0014 for errors of 1st order. This means that k1-α = 3.000. 2-1-5-5 Calculation of the limit of decision The limits of decision DU-238, DU-235 and DU-234 can be calculated with the following equations: t ⋅ 1 + M t0 DU − 238 = k1−α ⋅ AU − 232 C 0,U − 238 ⋅ M ⋅ C n ,U − 232 tM DU − 235 = C 0,U − 235 k 1−α ⋅ AU − 232 ⋅ ρ U − 235 ⋅ M ⋅ C n,U − 232 tM DU − 234 = k1−α ⋅ AU − 232 C 0,U − 234 ⋅ M ⋅ C n ,U − 232 tM C T ,U − 238 + tM t ⋅ 1 + M t0 t ⋅ 1 + M t0 C T ,U − 235 + tM C T ,U − 234 + tM 2-1-6 Quality Control Quality control measurements are necessary to provide documentation to show the reliability of the achieved results. The results reliability is a function of precision (reproducibility) and accuracy (the closeness to the true value). Precision can easily be determined by additional 16 internal determinations. The accuracy of the results can be determined through performing control analysis with reference materials that are as similar as possible to the analyzed material samples, and through participating in inter-comparison and/or proficiency measurements at least once per year. After performing 10-12 assays, a blank has to be performed with the same equipment and the same chemicals to ensure that there is no cross contamination. A blank is always recommended when samples with high uranium content have been analyzed or when there are symptoms for a contamination of the laboratory, the equipment, or the chemicals. The status of the equipment should be checked routinely by measuring background, blanks and standards. These results often give the first indication of analytical difficulties. Analytical control samples generally constitute about 10-15 % of the total samples. 2-1-7 References • R. Winkler, E. Frenzel, H. Rühle, J. Steiner: Schnellmethoden zur Analyse von Plutonium und anderen Aktiniden in Umweltproben. Publikationsreihe Fortschritte im Strahlenschutz, FS-90-51-AKU, Verlag TÜV Rheinland, Köln 1991 • Meßanleitungen für die Überwachung der Radioaktivität in der Umwelt und zur Erfassung radioaktiver Emissionen aus kerntechnischen Anlagen (Herausgeber: Der Bundesminister für Umwelt, Naturschutz und Reaktorsicherheit), Gustav Fischer Verlag, Stuttgart, Jena, New York 1995 • E. Holm: Review of Alpha-Particle Spectrometry Measurements of Actinides. • Int. J. Appl. Radiat. Isot. 35, 285-290 (1984) • O. Frindik: Alphaspektrometrische Methode zur Bestimmung von Plutonium und Uran in Lebensmitteln, biologischem Material und Böden. BFE-Bericht 1980/6, Karlsruhe 1980 • M. Pimpl, B. Yoo, I. Yordanova: Optimization of a Radioanalytical Procedure for the Determination of Uranium Isotopes in Environmental Samples. J. Radioanalyt. Nucl. Chem., Articles, 161 (No. 2), 437-441 (1992). 17 2-2 DETERMINATON OF THORIUM ISOTOPES 2-2-1 INTRODUCTION: Thorium (chemical symbol Th) is a naturally occurring radioactive metal found at very low levels in soil, rocks and water. It has several different isotopes, both natural and manmade, all of which are radioactive. Mineral such as monazite, thorite and thorianite are rich in thorium and may be mined for the metal. Generally, artificial isotopes come from decay of other man-made radionuclides, or absorption in nuclear reactions. Naturally, it exists as six isotopes (234Th, 232 Th, 231 Th, 230 Th, 228 Th and 227 Th) and found in the three natural decay series (238U series, 235U series and 232Th series). The most common form of thorium is thorium 232, found naturally. Thorium-232 has a half life time of 14 109 y, and decays by alpha emission, with accompanying gamma radiation. Thorium-232 is the top of a long decay series that contains key radionuclides such as radium-228 and radon-220. Two other isotopes of thorium, which can be significant in the environment, are 230 Th (75400 y)and 228 Th (1.9 y). Both decay by alpha emission, with accompanying gamma radiation. The 4+ oxidation state is the only oxidation state of thorium. It is quit insoluble. Although transport of thorium can occur by the movement of particulate matter to which thorium is adsorbed. 2-2-2 PRINCIPLE OF THE ANALYTICAL PROCEDURE: The ashed sample is spiked with thorium tracer (229Th) for chemical yield and activity calculation. The ashed sample is dissolved using HNO3, HCl and HF acids. Thorium in the dissolved sample solution is extracted from most of the matrix elements with TOPO (Trioctylphosphine oxide) and backextracted with 1M NH4F/0.1 M HCl solution. The thorium fraction is purified by coprecipitation with LaF3 and anion exchange. Finally, the pure thorium fraction is electrodeposited on a stainless steel disk and measured by mean of alpha spectrometry. 2-2-3 SAMPLE PREPARATION: 2-2-3-1 Soil and Sediment Samples 11. Dry the sample at 110 0C until the weight remains constant, then ground, homogenize and sieve the dried sample through a 2 mm sieve. 12. Weigh about 10 g of dried sample and moisture it with HNO3 till no further reaction occurs. Dry the sample on a sand bath. 18 13. Ash the dried sample at 550 0C at least for 6-8 hours. Ground and homogenize the sample ash. Note (A): If the residue is not free of organic carbon, which can be recognized by a dark brown or black coloured ash, then repeat the ashing process again. 14. Weigh up to 5 g ashed sample into a Pt- or Teflon dish and add 229 Th tracer (50-100mBq) for chemical yield determination. 15. Add 40 ml HNO3 and 10 ml HF, and digest on a medium temperature (70-800C) hot plate. 16. Repeat step (5) until no further dissolution takes place (white residue). 17. Add 3 ml HNO3 (65%) for three times and evaporate to near dryness. 18. Dissolve the sample residue in 100 ml 8 M HNO3 in a 250 ml glass beaker and cover it with a watch glass. 19. Boil the sample solution for 30 min., cool it to room temperature and adjust the solution volume to 100 ml 20. Continue with determination. 2-2-3-2 Biological Sample Materials (plants, milk, meat and fish) 2-2-3-2-1 Plants: 9. Dry the sample at 110 0C until the weight remains constant, then ground and homogenize the dried sample. 10. Ash the dried sample material at 550 0C at least for 6-8 hours. Ground and homogenize the sample ash (see Note A) . 11. Weigh up to 20 g of ashed sample material into an Erlenmeyer flask (1 L) and add 229 Th tracer (50-100 mBq) for chemical yield determination. 12. Add 100 ml of HNO3 and digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 13. Repeat the addition of HNO3 and digestion till you have a clear solution. 14. Evaporate the solution to near dryness and dissolve the sample residue in 100 ml 8M HNO3 in a 250 ml glass beaker and cover it with a watch glass. 15. Boil the sample solution for 30 min., cool it to room temperature and adjust the solution volume to 100 ml 19 16. Continue with determination. 2-2-3-2-2 Milk: 9. Dry up to 3 l of milk under an infrared lamp in a porcelain dish. 10. Cover the samples with HNO3 (65%) and add 229Th tracer (50-100 mBq) for chemical yield determination. 11. Digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 12. Repeat the addition of HNO3 and digestion till you have a clear solution. 13. Evaporate the solution to near dryness and ash the residue at 550 0C for 6-8 hours (see Note A). 14. Dissolve the sample residue in 100 ml 8M HNO3 in a 250 ml glass beaker and cover it with a watch glass. 15. Boil the sample solution for 30 min., cool it to room temperature and adjust the solution volume to 100 ml 16. Continue with determination. 2-2-3-2-3 Meat and fish: 9. Cut up to 100 g of the sample to small pieces and transfer it into a 2 l beaker. 10. Cover the samples with HNO3 (65%) and add 229Th tracer (50-100 mBq) for chemical yield determination. 11. Digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 12. Repeat the addition of HNO3 and digestion till you have a clear solution. 13. Evaporate the solution to near dryness and ash the residue at 550 0C for 6-8 hours (see Note A). 14. Dissolve the sample residue in 100 ml 8M HNO3 in a 250 ml glass beaker and cover it with a watch glass. 15. Boil the sample solution for 30 min., cool it to room temperature and adjust the solution volume to 100 ml 16. Continue with determination. 20 Schematic Representation of the Radiochemical Procedure of Thorium Ashed Samples Material add yield tracer Th-229 Digestion with HNO3,HCl and HF Dissolved Sample Material Extraction with TOPO/Cyclohexane Aqueous Phase : discard Organic Phase: wash 3 times with 3 M HCl Backextraction with HN4F/HCL Organic Phase: discard Aqueous Phase: wash 3 times with CHCl3 add TiCl3, La(NO3)3, HF Coprecipitation with LaF3 wash precipitation with 1.5 M HF dissolve in H3BO3 (saturated)/HNO3 (65%) Anion-Exchange Dowex 1x2, 50 - 100 mesh NO3- form wash with 8 M HNO3 elute with 9M HCl evaporate to dryness dissolve with 4 M H2SO4 add electrolytic solution, pH=1.7 Electrodeposition Alpha-Spectrometry 21 2-2-4 DETERMINATION: 1. Transfer the dissolved sample into a 250 ml separation funnel. 2. Extract thorium isotopes with 25 ml 0.2 M TOPO/Cyclohexane by shaking for 15 min each. 3. After phase separation, transfer the organic phase into another 250 ml separation funnel. 4. Extract again thorium isotopes with 25 ml 0.2 M TOPO/Cyclohexane by shaking for 15 min each. Combine the organic phases in the 250 ml separation funnel. Discard the aqueous phase. 5. Wash the organic phase three times with 50 ml 3 M HCl by shaking for 5 minutes each. Discard the washing solutions. 6. Backextract thorium isotopes two times with 25 ml 1 M NH4F / 0.1 M HCl by shaking for 15 min each. Combine the aqueous phases and discard the organic phase. 7. Wash the aqueous phase two times with 50 ml CHCl3 by shaking for 2 min each. Discard the organic phases. 8. Transfer the solution into a 100 ml polyethelene centrifuge tube. 9. Add 20 ml HF (40%) and 2 ml La(NO3)3 (25 mg La3+/ml). After a short interval of agitation, centrifuge the sample solution for 5 minutes at 3000 rpm to separate the fine crystalline precipitate. 10. Repeat the addition of two times 2 ml La(NO3)3 (25 mg La3+/ml) each, centrifuge the sample solution for 5 minutes at 3000 rpm then discard the aqueous phase after decanting. 11. Wash the precipitate carefully with 15 ml 1.5 M HF and centrifuge the sample solution for 5 min at 3000 rpm. Discard the aqueous phase after decanting. 12. Dissolve the precipitate in 10 ml hot saturated HBO3 and 10 ml concentrated HNO3. Cool the sample solution to room temperature. Column Preparation: Transfer about 1 g Dowex (1 x 2, 50-100 mesh, NO3-form) with distilled water into a glass column of 15 cm length with inner diameter of 8mm. Condition the column by passing 50 ml 8 M H NO3 at a rate of 1 ml/min. 13. Pass the sample 1ml/min. through the conditioned anion exchanger column at a rate of 22 14. Wash the column with 50 ml 8 M H NO3 at a rate of 1 ml/min. Discard the washing solutions. 15. Elute thorium isotopes with 50 ml 9 M HCl in a crystallizing dish. 16. Evaporate to dryness. Add twice 1 ml H2SO4 and fume to dryness each time. 17. Rinse carefully the cold crystallizing dish with 1 ml H2SO 4and transfer the solution into a cleaned electrolytic cell for electro-deposition on a stainless steel plate. 18. Electroplating solution: 30 g Ammonium oxalate (NH4)2(COO)2.H2O, 50 g Ammonium Sulfate (NH4)2 SO4, 1 g Hydroxyl- Ammonium Sulfate (NH3OH)2SO4 , 2 g DTPA (Diethyltriaminopenta acetic acid) Dissolved and filled up to one liter H2O adjusted to pH =1.7 with 0.5 M H2SO4 . 19. Rinse the crystallizing dish again three times with 1 ml electrolytic solution, pH =1.7, each and transfer the solutions into the cell. 20. Perform electro-deposition for 3 hours with 300 mA. 21. Before switching off the current, add 1 ml NH3, 25 %, and continue the electrolysis for 1 min. 22. Discard the solution, then rinse the cell with distilled H2O, discard the water and then disconnect the current. 23. Remove the stainless steel disk out of the cell and rinse it with distilled H2O and then ethanol. 24. Measure the alpha activity on the stainless steel disk by mean of alpha spectrometry. 2-2-5 Calculation of the Results 2-2-5-1 Calculation of the Chemical Yield η= where: η Cn,Th-229 CEx,Th-229 C n ,Th − 229 C Ex ,Th − 229 ⋅ 100 chemical yield, in % measured net count rate in the Th-229-Peak, in s-1 expected count rate in the Th-229-Peak, in s-1 C Ex ,Th − 229 = ATh − 229 ⋅ t M ⋅ ε ATh-229 added Th-229-activity, in Bq 23 tM ε time of measurement of the sample, in s counting efficiency of the measuring device 2-2-5-2 Calculation of thorium isotopes specific activities in the sample; The activities are calculated as it is done commonly for isotope dilution analysis: ATh − 232 = ATh − 230 = ATh − 228 = where: ATh-232 ATh-230 ATh-228 M CTh-232 C0,Th-232 CTh-230 C0,Th-230 CTh-228 C0,Th-228 CTh-229 C0,Th-229 CT,Th-232 CT,Th-230 CT,Th-229 CT,Th-228 ATh-229 M ⋅ (CTh − 229 ATh − 229 ⋅ [CTh − 232 − C 0,Th − 232 − CT ,Th − 232 ] − C 0,Th − 229 − CT ,Th − 229 ) ⋅ M ⋅ (CTh − 229 M ⋅ (CTh − 229 ATh − 229 ⋅ [CTh − 230 − C 0,Th − 230 − CT ,Th − 230 ] − C 0,Th − 229 − CT ,Th − 229 ) ATh − 229 ⋅ [CTh − 228 − C 0,Th − 228 − CT ,Th − 228 ] − C 0,Th − 229 − CT ,Th − 229 ) specific activity or concentration of Th-232, in Bq/g or Bq/l specific activity or concentration of Th-230, in Bq/g or Bq/l specific activity or concentration of Th-228, in Bq/g or Bq/l amount of sample taken for analysis, in g or l count rate in the Th-232-peak, in s-1 background count rate in the Th-232-peak, in s-1 count rate in the Th-230-peak, in s-1 background count rate in the Th-230-peak, in s-1 count rate in the Th-228-peak, in s-1 background count rate in the Th-228-peak, in s-1 count rate in the Th-229-peak, in s-1 background count rate in the Th-229-peak, in s-1 background in the Th-232-Peak, in s-1 (count rate, which is not produced by the decay of Th-232, but is a consequence of peak tailing) background from peak tailing in the Th-230-Peak, in s-1 background from peak tailing in the Th-229-Peak, in s-1 background from peak tailing in the Th-228-Peak, in s-1 activity of Th-229, added for yield determination, in Bq 2-2-5-3 Calculation of the standard deviation; The standard deviations of the thorium isotopes activities are obtained with the following equations: 24 2 s D ,Th − 232 ATh − 229 CTh − 232 C 0,Th − 232 C T ,Th − 232 C n ,Th − 232 = ⋅ + + + M ⋅ C n ,Th − 229 tM t0 tM C n ,Th − 229 CTh − 229 C 0,Th − 229 C T ,Th − 229 ⋅ + + t t t M 0 M s D ,Th − 230 ATh − 229 CTh − 230 C 0,Th − 230 C T ,Th − 230 C n ,Th − 230 = ⋅ + + + C M ⋅ C n ,Th − 229 tM t0 tM n ,Th − 229 CTh − 229 C 0,Th − 229 C T ,Th − 229 ⋅ + + t t0 tM M s D ,Th − 228 ATh − 229 C Th − 228 C 0,Th − 228 C T ,Th − 228 C n ,Th − 228 C Th − 229 C 0,Th − 229 CT ,Th − 229 ⋅ = ⋅ + + + + + M ⋅ C n ,Th − 229 tM t0 tM t0 tM C n ,Th − 229 t M 2 2 where: sD,Th-232 sD,Th-230 sD,Th-228 Cn,Th-232 Cn,Th-230 Cn,Th-228 Cn,Th-229 tM t0 standard deviation of the Th-232 specific activity or concentration, in Bq/g or Bq/l standard deviation of the Th-230 specific activity or concentration, in Bq/g or Bq/l standard deviation of the Th-228 specific activity or concentration, in Bq/g or Bq/l net count rate in the Th-232-Peak net count rate in the Th-230-Peak net count rate in the Th-228-Peak net count rate in the Th-229-Peak time of measurement of the sample, in s time of measurement of the background, in s 2-2-5-4 Calculation of the lower limit of detection (according to German standard DIN 25 482) , DTh − 232 = , DTh − 230 = , DTh − 228 = (k 1−α + k1− β ) ⋅ ATh − 229 M ⋅ C n ,Th − 229 (k 1−α + k1− β ) ⋅ ATh − 229 M ⋅ C n ,Th − 229 (k 1−α + k 1− β ) ⋅ ATh − 229 M ⋅ C n,Th − 229 ⋅ C 0,Th − 232 t M ⋅ 1 + tM t0 C T ,Th − 232 + tM ⋅ C 0,Th − 230 t M ⋅ 1 + tM t0 C T ,Th − 230 + tM ⋅ C 0,Th − 228 t M ⋅ 1 + tM t0 C T ,Th − 228 + tM where: k1-α Quantil of the Gaussian distribution for errors of 1st order (preselect risk for concluding falsely that activity is present) k1-β Quantil of the Gaussian distribution for errors of 2nd order (predetermined degree of confidence for detecting the presence of activity) 25 DIN 25 482-1 recommends for the errors of 1st and 2nd order a probability of 0.05. This means that k1-α = k1-β = 1.645 at the 95 % confidence level. The alpha-spectra of blank samples very often show more counts than background measurements of clean stainless steel plates. This means that the analytical procedure is not able to separate other alpha emitting nuclides completely. To minimize the risk that you falsely conclude that activity is present, it is advisable to pre-select an error probability of 0.0014 for errors of 1st order. This means that k1-α = 3.000. 2-2-5-5 Calculation of the limit of decision The limits of decision DTh-232, DTh-230 and DTh-228 can be calculated with the following equations: DTh − 232 = k 1−α ⋅ ATh − 229 C 0,Th − 232 ⋅ M ⋅ C n,Th − 229 tM t ⋅ 1 + M t0 C T ,Th − 232 + tM DTh − 230 = k 1−α ⋅ ATh − 229 C 0,Th − 230 ⋅ M ⋅ C n,Th − 229 tM t ⋅ 1 + M t0 C T ,Th − 230 + tM DTh − 228 = k1−α ⋅ ATh − 229 C 0,Th − 228 ⋅ M ⋅ C n,Th − 229 tM t ⋅ 1 + M t0 C T ,Th − 228 + tM 2-2-6 Quality Control Quality control measurements are necessary to provide documentation to show the reliability of the achieved results. The results reliability is a function of precision (reproducibility) and accuracy (the closeness to the true value). Precision can easily be determined by additional internal determinations. The accuracy of the results can be determined through performing control analysis with reference materials that are as similar as possible to the analyzed material samples, and through participating in inter-comparison and/or proficiency measurements at least once per year. After performing 10-12 assays, a blank has to be performed with the same equipment and the same chemicals to ensure that there is no cross contamination. A blank is always recommended when samples with high thorium content have been analyzed or when there are symptoms for a contamination of the laboratory, the equipment, or the chemicals. 26 The status of the equipment should be checked routinely by measuring background, blanks and standards. These results often give the first indication of analytical difficulties. Analytical control samples generally constitute about 10-15 % of the total samples. 2-2-7 References • R. Winkler, E. Frenzel, H. Rühle, J. Steiner: Schnellmethoden zur Analyse von Plutonium und anderen Aktiniden in Umweltproben. Publikationsreihe Fortschritte im Strahlenschutz, FS-90-51-AKU, Verlag TÜV Rheinland, Köln 1991 • Meßanleitungen für die Überwachung der Radioaktivität in der Umwelt und zur Erfassung radioaktiver Emissionen aus kerntechnischen Anlagen (Herausgeber: Der Bundesminister für Umwelt, Naturschutz und Reaktorsicherheit), Gustav Fischer Verlag, Stuttgart, Jena, New York 1995 • E. Holm: Review of Alpha-Particle Spectrometry Measurements of Actinides. • Int. J. Appl. Radiat. Isot. 35, 285-290 (1984) • Durham R.W., Joshi S.R. Determination of Th-228, Th-230 and Th-232 in Environmental Samples from Mining and Milling Operations. J. Radioanal. Chem. 52, 181-188, 1979. • Frindik O., Thorium in Böden, Gemüse, Getreide und Obst. Z. Lebensm. Unters. Forsch. 189, 236-240, 1989. • Frindik O., Thorium and Uran in Lebensmitteln tierischer Herkunft. Z. Lebensm. Unters. Forsch. 194, 377-380, 1992. 27 2-3 DETERMINATON OF LEAD-210 2-3-1 INTRODUCTION: Lead-210 (physical half-life time, 22.2 y) occurs naturally as one of the decay products of the 238 U series. Disequilibrium between 210 Pb and its parent nuclide, 226 Ra (physical half- life time, 1600 y), arises through the diffusion of the intermediate gaseous isotope, (physical half life-time, 3.8 d). A fraction of 222 222 Rn Rn atoms diffuse into the atmosphere and its decay products (mainly 210Pb and its daughter 210Po) are removed from the atmosphere by wet and dry deposition. Measurements of 210 Pb have found extensive applications in the 210 Pb geo-chronometry of rapidly accumulating sediment environment, as well as in studies of the behavior of aerosols in the atmosphere. Also, 210Pb and its grand daughter radionuclide (210Po) are included in the group of most highly toxic radioisotopes and provide the major natural radiation dose to man. For the determination of 210 Pb, stable lead is used as a carrier and tracer. Where possible a source of stable lead should be used, which is old enough that most of the 210 210 Pb activity was decayed. Lead-210 is determined via beta counting of its daughter Bi after build up time (at least two weeks) using a low background gas proportional counter. 2-3-2 PRINCIPLE OF THE ANALYTICAL PROCEDURE: After addition of Pb2+ carrier to the ashed sample, the ashed sample is dissolved. Lead is leached with HBr as tetrabromo-complex, extracted with trioctylamin/toluene and backextracted with HCl. After addition of Bi3+ carrier, Bi3+ traces are separated by precipitation as BiOCl. Finally lead is precipitated as PbCrO4 and collected on a filter paper. After waiting for 8-10 days, the filter is covered with a filter paper of equal size to hold back the low energy beta particles of 210Pb and the alpha particles of ingrown 210Po. The high energy beta particles of 210Bi are counted using a calibrated low background gas proportional counter. 2-3-3 SAMPLE PREPARATION: 2-3-3-1 Soil and Sediment Samples 1. Dry the sample at 110 0C until the weight remains constant, then ground, homogenize and sieve the dried sample through a 2 mm sieve. 2. Weigh about 10 g of dried sample and moisture it with HNO3 (65%) till no further reaction occurs. Dry the sample on a sand bath. 3. Ash at 550 0C at least for 6-8 hours. Ground and homogenize the sample ash. 28 Note (A): If the residue is not free of organic carbon, which can be recognized by a dark brown or black coloured ash, then repeat the ashing process again. 4. Weigh up to 5 g ashed sample into a Pt- or Teflon dish and add 1ml of Pb carrier solution (20 mg/ml) for chemical yield determination. 5. Add 40 ml HNO3 (65%) and 10 ml HF (40%), and digest on a medium temperature (70-80 0C) hot plate. 6. Repeat the digestion with HNO3 and HF until no further dissolution takes place (white residue). 7. Add 3 ml HNO3 for three times and evaporate to near dryness. 8. Continue with determination. 2-3-3-2 Biological Sample Materials (plants, milk, meat and fish) 2-3-3-2-1 Plants: 1. Dry the sample at 110 0C until the weight remains constant, then ground and homogenize. 2. Weigh up to 100 g of dried sample material into an Erlenmeyer flask (1 L) and add 1ml of Pb carrier solution (20 mg/ml) for chemical yield determination. 3. Add 100 ml of HNO3 and digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 4. Repeat the addition of HNO3 and digestion till you have a clear solution. 5. Evaporate the solution to near dryness and ash the residue at 550 0C for 6-8 hours (see Note A). 6. Continue with determination. 2-3-3-2-2 Milk: 1. Dry up to 3 l of milk under an infrared lamp in a porcelain dish. 2. Transfer the dried sample material into an Erlenmeyer flask (1 L) and add 1ml of Pb carrier solution (20 mg/ml) for chemical yield determination. 3. Add 100 ml of HNO3 and digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 29 4. Repeat the addition of HNO3 and digestion till you have a clear solution. 5. Evaporate the solution to near dryness and ash the residue at 550 0C for 6-8 hours (see Note A). 6. Continue with determination. 2-3-3-2-3 Meat and fish: 1. Cut up to 100 g of the sample to small pieces and transfer it into 2 l beaker. 2. Cover the samples with HNO3 (65%) and add 1ml of Pb carrier solution (20 mg/ml) for chemical yield determination. 3. digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 4. Repeat the addition of HNO3 and digestion till you have a clear solution. 5. Evaporate the solution to near dryness and ash the residue at 550 0C for 6-8 hours (see Note A). 6. Continue with determination. 30 Schematic Representation of the Radiochemical Procedure of Lead Ashed Sample Material add yield tracer Pb2+ digest with HNO3, HCl and HF fume off with HBr (47%) leach with 3 M HBr Dissolved Sample Solution Aqueous phase: discard Extraction with TOA/Toluene Organic phase: wash with 0.1 M HBr Organic phase: discard Back-extraction with HCl (32%) Aqueous phase: wash with CHCl3 add Bi3+ - carrier and HNO3 evaporate to dryness dissolve in HCl(32%) dilute with H2O, adjust pH=8 with NH3 Bi/Pb- Precipitation supernatant solution: discard dissolve precipitation with HCl (32%) dilute with H2O Pb/Bi- Precipitation Note date and time filtrate, discard the precipitation add 5 g CH3COONH4 heat to boiling, add Na2CrO4 solution PbCrO4 - Precipitation Filtrate Wash filter with Ethanol/Acetone Determine chemical yield by weighing After 8-10 days Cover precipitate with filter paper Gross- Beta Measurement Calculate 210Pb activity from measured 210Bi activity 31 2-3-4 DETERMINATION: 1. Transfer the dissolved sample into a 400 ml glass beaker, cover it with HBr (47%) and fume it off to dryness. 2. Dissolve the sample in 100 ml 3 M HBr (aqueous phase). Filtrate the solution, if necessary, and wash the filter with 5 ml 3 M HBr. Trioctylamine/Toluene (organic phase) preparation: Shake 75ml of organic phase twice with 75 ml 1.5 HBr for 30 s each in a 250 ml separating funnel, then discard the HBr solution. 3. Transfer the aqueous phase to the separating funnel with the organic phase, then extract lead by shaking for 30 s and discard the aqueous phase. 4. Wash the organic phase three times with 50 ml 0.1 M HBr for 30 s each and discard the washing solutions. 5. Back-extract lead with 50 ml 32% HCl by shaking for 30 s. Discard the organic phase. 6. Wash the aqueous phase twice with 50 ml CHCl3 by shaking for 30 s each. Discard the organic phases. 7. Transfer the solution into a 400 ml glass beaker. Add 1 ml Bi3+ - carrier (20 mg/ml) and 50 ml 65% HNO3, and evaporate the solution to dryness on the sand bath. 8. Dissolve the residue in 1 ml 32% HCl and transfer it with 30 ml H2O to a centrifuge tube. Adjust the pH to 8 with 1-2 ml NH3 using phenolphthalein as indicator (red colour). 9. Under occasional stirring, warm the sample in a water bath for 10 min., then cool it in an ice bath for 10 min and subsequently centrifuge for 5 min. at 3000 rpm. Discard the supernatant solution. 10. Add 5 drops 32% HCl to the light yellow residue and dissolve it. Add 40 ml H2O. 1. Pb-Bi SEPARATION: NOTE DATE AND TIME 11. Under occasional stirring, warm the sample in a water bath for 10 min., then cool it in an ice bath for 10 min and subsequently centrifuge for 5 min. at 3000 rpm. Filtrate the supernatant with Pb2+ in a 250 ml beaker. 12. Dissolve BiOCl precipitate and re-precipitate two times according to steps 10 and 11. 13. Add 5 g Ammonium-acetate to the Pb2+ containing solution. Cover the beaker with a watch glass and heat up to boiling, then add 1 ml Na2CrO4 30% solution and let it boil for 15 min. Cool down the solution to room temperature. 32 1. FILTER PREPARATION: wash the filter paper ( blue band, about 48mm diameter) with H2O, ethanol and acetone, 20 ml each. Dry the filter for 20 min. at 110 0C and cool it down to room temperature in a desiccator. Weigh the empty filter. 14. Filtrate the solution over the prepared filter. Wash the filter with the yellow precipitation with H2O, ethanol and acetone, 20 ml each. Dry the filter for 20 min. at 110 0C and cool it down to room temperature in a desiccator. Weigh the filter with the precipitate. 15. Preserve the filter in a desiccator at least for 8-10 days for 210 Bi ingrowth. Cover the filter with a filter of the same size and measure it using a low level proportional gas beta counter. Bi MEASUREMENT: Note date, time and measuring time 2-3-5 Calculation of the results: 2-3-5-1 Determination of the chemical yield; η chem = (WF + P − WF ) ∗ 0.641 Vcarrier ∗ M carrier where: WF+P WF 0.641 Vcarrier Mcarrier weight of filter with precipitation in g weight of the empty filter conversion factor: Pb-chromate to Pb2+ added volume of Pb-carrier solution in l concentration of Pb2+ in the carrier solution in g/l 2-3-5-2 Calculation of 210Pb specific activity in the sample; APb − 210 = Where: APb-210 M ε RG − R0 M ∗ ε ∗η chem (1 − e −λ ( Bi −210 )∗∆t ) Pb-210 activity in Bq/g or Bq/l amount of sample taken for analysis in g or l mean counting efficiency of the counter used 33 ηchem RG R0 λ(Bi-210) ∆t T1 T2 TM chemical yield gross count rate of the sample in s-1 background count rate of the counter in s-1 decay constant of Bi-210 in s-1 (=1.6.10-6) T1+1/2. TM –T2 date and time of starting the measurement date and time of the Pb/Bi- separation counting time in s. 2-3-5-3 Calculation of the standard deviation S A, Pb− 210 = RG R0 1 ∗ + −λ ( Bi − 210 )∗∆t M ∗ ε ∗η chem ∗ (1 − e tm t0 ) 2-3-5-4 Calculation of the lower limit of detection (according to German standard DIN 25 482) LLD A, Pb − 210 = k1-α k1-β k1−α + k1− β M ∗ ε ∗η chem ∗ (1 − e −λ ( Bi − 210 )∗∆t ) ∗ R0 t0 t ∗ 1 + 0 tm Quantil of the Gaussian distribution for errors of 1st order (preselect risk for concluding falsely that activity is present) Quantil of the Gaussian distribution for errors of 2nd order (predetermined degree of confidence for detecting the presence of activity) DIN 25 482-1 recommends for the errors of 1st and 2nd order a probability of 0.05. This means that k1-α = k1-β = 1.645 at the 95 % confidence level. The beta measurements of blank samples very often show more counts than background measurements of empty filters. This means that the analytical procedure is not able to separate other beta emitting nuclides completely. To minimize the risk that you falsely conclude that activity is present, it is advisable to pre-select an error probability of 0.0014 for errors of 1st order. This means that k1-α = 3,000. 2-3-6 Quality Control Quality control measurements are necessary to provide documentation to show the reliability of the achieved results. The results reliability is a function of precision (reproducibility) and accuracy (the closeness to the true value). Precision can easily be determined by additional internal determinations. The accuracy of the results can be determined through performing control analysis with reference materials that are as similar as 34 possible to the analyzed material samples, and through participating in inter-comparison and/or proficiency measurement at least once per year. After performing 10-12 assays, a blank has to be performed with the same equipment and the same chemicals to ensure that there is no cross contamination. A blank is always recommended when samples with high lead content have been analyzed or when there are symptoms for a contamination of the laboratory, the equipment, or the chemicals. The status of the equipment should be checked routinely by measuring background, blanks and standards. These results often give the first indication of analytical difficulties. Analytical control samples generally constitute about 10-15 % of the total samples. 2-3-7 References • Gibson, W., The radiochemistry of Lead, Report NAS-NS-3040 • Kolthoff, I.M., Elving, P.J. (1964). A systematic analytical chemistry of the elements: Part 2, Vol. 6, 71-175 (Gilbert T.W.) Interscience publishers. • Godoy, J.M. (1983). Development of an analysis method for the determination of 238U, 234U, 232Th, 230Th, 228Th, 228Ra, 226Ra, 210Pb and 210Po and their application on environmental samples. KFK- Report 3502. • International Atomic Energy Agency (1989). Measurement of radionuclides in food and the environment. Technical Report Series No. 295. 35 2-4 DETERMINATON OF POLONIUM-210 2-4-1 INTRODUCTION: Polonium-210 (physical half life time, 138 d) is the last radioactive member of the 238 U decay series and is the only naturally occurring polonium isotope with a sufficiently long half-life time to allow its measurement. It is an alpha emitting radionuclide. It is present in trace amounts in most plants and foodstuffs as well as in human tissues. The polonium isotopes are amongst the most radiotoxic nuclides to human beings. 210 Po is reported to account for up to 75% of the alpha-radiation in marine organisms and up to 50% of the internal alpha-radiation dose in people. Of the 26 known radioactive polonium isotopes, only 208 Po (2.9 y, 4.9 MeV) and 209Po (109 y, 5.12 MeV) have physical half-life times long enough to make them useful as internal tracers. The 208 Po is preferred because it is more easily available and in case of contamination, it is decontaminated easier than 209 Po because of its relatively short half-life time. 2-4-2 PRINCIPLE OF THE ANALYTICAL PROCEDURE: The dried sample is spiked with polonium tracer (208Po or 209 Po). The sample is dissolved using mineral acid (HNO3,HCl and HF). Polonium isotopes are quantitatively deposited on a stainless steel, silver, cupper or nickel disk. The deposition is very specific and can be carried out in the presence of other radionuclides. By rapid rotation of the stainless steel disk during deposition, polonium is recovered efficiently from diluted HCl solution as a thin and uniform activity deposit suitable for high resolution alpha spectrometry. 2-4-3 SAMPLE PREPARATION: 2-4-3-1 Soil and Sediment Samples 1. Dry the sample at 110 0C until the weight remains constant, then ground, homogenize and sieve the dried sample through a 2 mm sieve. 2. Weigh up to 3 g dried sample into a Pt- or Teflon dish and add an aliquot (50-100 mBq) of Po tracer (209Po or 208Po) for chemical yield determination. 3. Add 40 ml HNO3 and 10 ml HF, and digest on a medium temperature (70-80 0C) hot plate. 4. Repeat the step (3), until no further dissolution takes place (white residue). 5. Add 3 ml HNO3 for three times and evaporate to near dryness. 6. Add 3 ml HCl for three times and evaporate to near dryness. 36 7. Continue with determination. 2-4-3-2 Biological Sample Materials (plants, milk, meat and fish) 2-4-3-2-1 Plants: 1. Dry the sample at 110 0C until the weight remains constant, then ground and homogenize. 2. Weigh up to 20 g of dried sample materials into an Erlenmeyer-flask (1 L) and add an aliquot (50-100 mBq) of Po tracer (209Po or 208Po) for chemical yield determination. 3. Add 100 ml of HNO3 and digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 4. Repeat the addition of HNO3 and digestion till you have a clear solution. 5. Add 3 ml HNO3 for three times and evaporate to near dryness. 6. Add 3 ml HCl for three times and evaporate to near dryness. 7. Continue with determination. 2-4-3-2-2 Milk: 1. Dry up to 3 l of milk under an infrared lamp in a porcelain dish. 2. Transfer the dried sample material into an Erlenmeyer flask (1 L) and add an aliquot (50-100 mBq) of Po tracer (209Po or 208Po) for chemical yield determination. 3. Add 100 ml of HNO3 and digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 4. Repeat the addition of HNO3 and digestion till you have a clear solution. 5. Add 3 ml HNO3 for three times and evaporate to near dryness. 6. Add 3 ml HCl for three times and evaporate to near dryness. 7. Continue with determination. 2-4-3-2-3 Meat and fish: 1. Cut up to 100 g of the sample to small pieces and transfer it into 2 l beaker. 2. Cover the samples with HNO3 (65%) and add an aliquot (50-100 mBq) of Po tracer (209Po or 208Po) for chemical yield determination. 3. Digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 4. Repeat the addition of HNO3 and digestion till you have a clear solution. 37 5. Add 3 ml HNO3 for three times and evaporate to near dryness. 6. Add 3 ml HCl for three times and evaporate to near dryness. 7. Continue with determination. Schematic Representation of the Radiochemical Procedure of Polonium Dried Sample Material Add yield tracer 208Po or 209Po Digest with HNO3, HCl and HF Fume off with HCl (32%) Dissolve in 0.5 M HCl Dissolved Sample Material Heat to boiling, Add 200 mg Ascorbic acid Po deposition on a rotating stainless steel disk Rotate the disk for one hour at 90 oC Alpha Spectrometry 2-4-4 DETERMINATION: 1. Transfer the dissolved sample quantitatively into a 80 ml glass beaker with 40 ml 0.5 M HCl and cover it with a watch glass. 2. Heat the solution to about 90 0C on a hot plate stirrer, add about 200 mg Ascorbic acid and immerse the Teflon holder with the stainless steel disc. Stir the holder for an hour at a speed that gives maximum agitation without splashing. 3. Pour off the solution in another beaker and reserve it for 210 Pb determination, if required. 4. Remove the disc, rinse it with HO2 then ethanol. Air dry the disc. 5. Measure the alpha activity on the stainless steel disk by mean of alpha spectrometry. 38 2-4-5 Calculation of the results: 2-4-5-1 Determination of the chemical yield; η chem = Rn , Po −tracer APo−tracer ∗ TM ∗ ε where: R n, Po-tracer A Po-tracer TM ε measured net count rate in the Po-tracer peak in s-1 activity of the Po-tracer in Bq time of measurement of the sample in s Counting efficiency of the measuring device. 2-4-5-2 Calculation of 210Po specific activity in the sample; APo − 210 = Where: Apo-210 M Rb,Po-tracer R0,Po-tracer Rb,Po-210 R0,Po-210 APo −tracer ∗ (Rb , Po − 210 − R0, Po −210 ) M ∗ ( Rb , Po−tracer − R0, Po −tracer ) Po-210 activity in Bq/g or Bq/l amount of sample taken for analysis in g or l count rate in the Po-tracer peak, s-1 background count rate in the Po-tracer peak, s-1 count rate in the Po-210 peak, s-1 background count rate in the Po-210 peak, s-1 2-4-5-3 Calculation of the standard deviation S A, Po− 210 Rb , Po −210 R0, Po −210 Rn , Po −210 APo −tracer = ∗ + + M ∗ Rn , Po −tracer tM t0 Rn , Po −tracer Where: Rn, Po-tracer Rn, Po-210 tM t0 net count rate in the Po-tracer peak, s-1, net count rate in the Po-210 peak, s-1, time of measurement of the sample, s, time of measurement of background, s, 2 Rb , Po −tracer R0, Po −tracer ∗ + t t0 M 39 2-4-5-4 Calculation of the lower limit of detection (according to German standard DIN 25 482) LLD A, Po − 210 = k1-α (k 1−α + k1− β ) ∗ APo −tracer M ∗ Rn , Po −tracer ∗ R0, Po − 210 t ∗ 1 + 0 tM tM Quantil of the Gaussian distribution for errors of 1st order (preselect risk for concluding falsely that activity is present) k1-β Quantil of the Gaussian distribution for errors of 2nd order (predetermined degree of confidence for detecting the presence of activity) DIN 25 482-1 recommends for the errors of 1st and 2nd order a probability of 0.05. This means that k1-α = k1-β = 1.645 at the 95 % confidence level. The alpha-spectra of blank samples very often show more counts than background measurements of clean stainless steel plates. This means that the analytical procedure is not able to separate other alpha emitting nuclides completely. To minimize the risk that you falsely conclude that activity is present, it is advisable to pre-select an error probability of 0.0014 for errors of 1st order. This means that k1-α = 3,000. 2-4-6 Quality Control Quality control measurements are necessary to provide documentation to show the reliability of the achieved results. The results reliability is a function of precision (reproducibility) and accuracy (the closeness to the true value). Precision can easily be determined by additional internal determinations. The accuracy of the results can be determined through performing control analysis with reference materials that are as similar as possible to the analyzed material samples, and through participating in inter-comparison and/or proficiency measurement at least once per year. After performing 10-12 assays, a blank has to be performed with the same equipment and the same chemicals to ensure that there is no cross contamination. A blank is always recommended when samples with high polonium content have been analyzed or when there are symptoms for a contamination of the laboratory, the equipment, or the chemicals. The status of the equipment should be checked routinely by measuring background, blanks and standards. These results often give the first indication of analytical difficulties. Analytical control samples generally constitute about 10-15 % of the total samples. 40 2-4-7 References • Hamilton T.F., Smith J.D., (1989). Improved alpha energy resolution for the determination of polonium isotopes by alpha spectrometry. Applied Radiation Isotopes, 37 (1), 17-27. • Godoy, J.M. (1983). Development of an analysis method for the determination of 238U, 234 U, 232Th, 230Th, 228Th, 228Ra, 226Ra, 210Pb and 210Po and their application on environmental samples. KFK- Report 3502. • International Atomic Energy Agency (1989). Measurement of radionuclides in food and the environment. Technical Report Series No. 295. • UNSCEAR, United Nations Scientific Committee on the Effect of Atomic Radiation, (1988). Source, effects, and risks of ionizing radiation. Report on general assembly with annexes, United Nations, New York. 41 3- MAN-MADE RADIONUCLIDES 3-1 DETERMINATON OF PLUTONIUM ISOTOPES 3-1-1 INTRODUCTION: Recent studies have confirmed that the earth crust and its surface contain only negligible quantities of natural plutonium. The sources of plutonium isotopes in nature nowadays are the atmospheric nuclear weapons testing, the burn up of a 238 Pu auxiliary powered navigational satellite (SNAP-9A), the nuclear fuel reprocessing plants, nuclear accident and the nuclear reactor influents. The determination of Pu in environmental samples is mainly directed to the alpha emitting isotopes and 240 238 Pu, 239 Pu Pu which have high radiotoxicity. However, the largest contributor to the total plutonium radioactivity in the environmental samples is the 241 Pu isotope, a beta emitter with a half-life of 14.4 years and maximum beta energy of 21 keV. Although the radiotoxicity of the 241 Pu itself is much lower than that of the alpha emitting plutonium isotopes, the ingrowth of 241 Pu daughter, 241 Am, an alpha emitter of high radiotoxicity, has to be considered. In the environment, the mean specific activity of the man-made 239 Pu isotope is very close to 10-13g/g (0.23 Bq/kg) for surface soil. In some places, nuclear weapon test sites, plutonium producing nuclear reactor sites and close to the chemical factories of plutonium extraction from the nuclear fuel elements, the specific activity of Pu can exceed the “normal” level by a factor greater than 102. The Pu isotopes activity ratios can provide information to identify of the source(s) of these isotopes in the environment. Global fallout has deposited Pu isotopes world wide. The 241Pu/239+240Pu and 238Pu/239+240Pu activity ratios vary very much depending on the origin of plutonium isotopes. For fresh fallout from nuclear weapon tests, the 241 Pu/239+240Pu activity ratio is about 12-16 and for spent nuclear fuel from power reactors about 130. 3-1-2 PRINCIPLE OF THE ANALYTICAL PROCEDURE: The ashed sample is spiked with plutonium tracer (236Pu or 242Pu) for chemical yield determination and activity calculation. The ashed sample is leached twice using HNO3/HF and HNO3/Al(NO3)3 solution mixtures, with the addition of NaNO2 which transfers Pu3+ to Pu4+. Plutonium is extracted from the leached sample solution with 42 TOPO (Trioctylphosphine Oxide, TOPO) and backextracted with ascorbic in HCl solution. The plutonium fraction is purified by coprecipitation with LaF3 and anion exchange. Finally, the pure Pu fraction is electrodeposited on a stainless steel disk from HCl/oxalate solution and measured using alpha spectrometry. 3-1-3 Samples preparation 3-1-3-1 Soil and Sediment Samples 1. Dry the sample at 110 0C until the weight remains constant, then ground, homogenize and sieve the dried sample through a 2 mm sieve. 2. Weigh about 120 g of dried sample and moisture it with HNO3 till no further reaction occurs. Dry the sample on a sand bath. 3. Ash the dried sample at 550 0C at least for 6-8 hours. Ground and homogenize the sample ash. Note (A): If the residue is not free of organic carbon, which can be recognized by a dark brown or black coloured ash, then repeat the ashing process again. 4. Weigh up to 100 g ashed sample into an Erlenmeyer-flask (1l) and add Pu tracer (50100 mBq) for chemical yield determination. 5. Add 290 ml 8 M HNO3/ 0.9 M HF and boil with stirring on a hot plate stirrer for 30 min 6. Add carefully to the hot solution 2.5 g NaNO2. Cool the solution to room temperature. 7. Filter the leached sample under pressure reduced using a Buchner funnel with a Whatman No. 42 filter paper. Transfer the solution into 600 ml glass beaker. Transfer the filter with the ashed sample residue back into the Erlenmeyer-flask (1l). 8. Add 250ml 5M HNO3/1M Al(NO3)3 and boil the sample solution with stirring on hot plate stirrer for 30 min. 9. Add carefully to the hot solution 2.5 g NaNO2. Cool the solution to room temperature. 10. Filter the leached solution under reduced pressure using a Buchner funnel with a Whatman No. 42 filter paper. Combine the leaching solutions. Discard the filter and the sample residue. 11. Continue with determination. 43 3-1-3-2 Biological Sample Materials (plants, milk, meat and fish) 3-1-3-2-1 Plants: 1. Dry the sample at 110 0C until the weight remains constant, then ground and homogenize. 2. Ash the dried sample material at 550 0C at least for 6-8 hours. Ground and homogenize the sample ash. 3. Weigh up to 20 g of ashed sample material into an Erlenmeyer flask (1 L) and add Pu tracer (50-100 mBq) for chemical yield determination. 4. Add 100 ml of HNO3 and digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 5. Repeat the addition of HNO3 and digestion till you have a clear solution. 6. Evaporate the solution to near dryness and dissolve the sample residue in 100 ml 8M HNO3. 7. Boil the sample solution and add carefully to the hot solution 2.5 g NaNO2. Cool the solution to room temperature. 8. Continue with determination. 3-1-3-2-2 Milk: 1. Dry up to 3 l of milk under an infrared lamp in a porcelain dish. 2. Cover the samples with HNO3 (65%) and add Pu tracer (50-100 mBq) for chemical yield determination. 3. Digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 4. Repeat the addition of HNO3 and digestion till you have a clear solution. 5. Evaporate the solution to near dryness and ash the residue at 550 0C for 6-8 hours. 6. Dissolve the sample residue in 100 ml 8M HNO3 . 7. Boil the sample solution and add carefully to the hot solution 2.5 g NaNO2. Cool the solution to room temperature. 8. Continue with determination. 3-1-3-2-3 Meat and fish: 1. Cut up to 100 g of the sample to small pieces and transfer it into a 2 l beaker. 2. Cover the samples with HNO3 (65%) and add Pu tracer (50-100 mBq) for chemical yield determination. 44 3. Digest on a medium temperature (70-80 0C) hot plate and stir using a Teflon-coated magnetic bar. 4. Repeat the addition of HNO3 and digestion till you have a clear solution. 5. Evaporate the solution to near dryness and ash the residue at 550 0C for 6-8 hours (see Note A). 6. Dissolve the sample residue in 100 ml 8M HNO3. 7. Boil the sample solution and add carefully to the hot solution 2.5 g NaNO2. Cool the solution to room temperature. 8. Continue with determination. 45 Schematic Representation of the Radiochemical Procedure of Plutonium Ashed Samples Material add yield tracer Pu-236 leaching with 8 M HNO3 / 0.9 M HF add NaNO2, filtrate leaching with 5 M HNO3/ 1 M Al(NO3)3 add NaNO2, filtrate Dissolved Sample Material Extraction with TOPO/Cyclohexane Aqueous Phase: discard Organic Phase: wash 3 times with 3 M HCl Backextraction with 0.5 M Ascorbic Acid/1 M HCl Organic Phase: discard Aqueous Phase: wash 3 times with CHCl3 Coprecipitation with LaF3 wash precipitation with 1.5 M HF dissolve in H3BO3 (saturated)/HNO3 (65%) add NaNO2 Anion-Exchange Dowex 1x2, 50 - 100 mesh wash with 7.2 M HNO3 wash with 9 MHCl eluate with 0.36 M HCl/0.01 M HF evaporate to dryness dissolve with 4 M HCl add (NH4)2C2O4 (4%) Electrodeposition Alpha-Spectrometry 46 3-1-4 DETERMINATION: 1. Transfer the dissolved sample into a separation funnel (250 or 1000 ml). 2. Extract plutonium isotopes with 25 ml 0.2 M TOPO/Cyclohexane by shaking for 15min. 3. After phase separation, transfer the organic phase into another 250 ml separation funnel. 4. Extract again plutonium isotopes with 25 ml 0.2 M TOPO/Cyclohexane by shaking for 15 min. Combine the organic phases in the 250 ml separation funnel. Discard the aqueous phase. 5. Wash the organic phase three times with 50 ml 3 M HCl by shaking for 5 minutes each. Discard the washing solutions. 6. Backextract plutonium isotopes two times with 25 ml 0.5 M Ascorbic acid/ 1 M HCl by shaking for 15 min each. Combine the aqueous phases in a 250 ml separation funnel and discard the organic phase. 7. Wash the aqueous phase two times with 50 ml CHCl3 by shaking for 2 min each. Discard the organic phases. 8. Transfer the solution into a 100 ml polyethelene centrifuge tube. 9. Add 20 ml HF (40%) and 2 ml La(NO3)3 (25 mg La3+/ml). After a short interval of agitation, centrifuge the sample solution for 5 minutes at 3000 rpm to separate the fine crystalline precipitate. 10. Repeat the addition of 2 ml La(NO3)3 (25 mg La3+/ml) two times, centrifuge the sample solution for 5 minutes at 3000 rpm then discard the aqueous phase after decanting. 11. Wash the precipitate carefully with 15 ml 1.5 M HF and centrifuge the sample solution for 5 minutes at 3000 rpm. Discard the aqueous phase after decanting. 12. Dissolve the precipitate in 10 ml hot saturated HBO3 and 10 ml concentrated HNO3. 13. Add 0.25 ml 1.5 M NaNO2 (freshly preparaed). Column Preparation: Transfer about 1 g Dowex (1 x 2, 50-100 mesh, NO3 form) with distilled water into a glass column of 15 cm length with inner diameter of 8mm. Condition the column by passing 50 ml 7.2 M HNO3 at a rate of 1 ml/min. 47 14. Pass the sample solution through the conditioned anion exchanger column at a rate of 1 ml/min. 15. Wash the column with 50 ml 7.2 M HNO3 at a rate of 1 ml/min. Discard the washing solutions. 16. Wash the column with 10 ml 9 M HCl at a rate of 1 ml/min. Discard the washing solutions. 17. Elute plutonium isotopes with 10 ml 0.36 M HCl/0.01 M HF in a crystallizing dish. 18. Evaporate the eluted solution to dryness. Add twice 1 ml HCl (32%) and fume to dryness each time. 19. Rinse carefully the crystallizing dish with 0.4 ml 4 M HCl and transfer the solution into a cleaned electrolytic cell for electrodeposition on a stainless steel plate. 20. Rinse the crystallizing dish again three times with 1 ml 4 % (NH4)2C2O4 each and transfer the solutions into the cell. 21. Rinse the crystallizing dish again with 0.6 ml distilled H2O and transfer the solution into the cell. 22. Perform electrodeposition for 2 hours with 300 mA. 23. Before switching off the current, add 1 ml NH3, 25 %, and continue the electrolysis for 1 min. 24. Discard the solution, then rinse the cell with distilled H2O, discard the water and then disconnect the current. 25. Remove the stainless steel disk out of the cell and rinse it with distilled H2O and then ethanol. 26. Measure the alpha activity on the stainless steel disk by mean of alpha spectrometry. 3-1-5 Calculation of the Results 3-1-5-1 Calculation of the Chemical Yield η= where: η Cn,Pu-236 CEx,Pu-236 C n , Pu − 236 C Ex , Pu − 236 ⋅ 100 chemical yield, in % measured net count rate in the Pu-236-Peak, in s-1 expected count rate in the Pu-236-Peak, in s-1 48 C Ex , Pu − 236 = APu − 236 ⋅ t M ⋅ ε added Pu-236-activity, in Bq time of measurement of the sample, in s counting efficiency of the measuring device APu-236 tM ε 3-1-5-2 Calculation of plutonium isotopes specific activities The activities are calculated as it is done commonly for isotope dilution analysis: APu − 239 + 240 = APu − 238 = where: APu-239+240 APu-238 M CPu-239+240 C0,Pu-239+240 CPu-238 C0,Pu-238 CPu-236 C0,Pu-236 CT,Pu-239+240 CT,Pu-238 CT,Pu-236 APu-236 APu − 236 ⋅ [C Pu − 239+ 240 − C 0, Pu − 239+ 240 − CT , Pu − 239+ 240 ] M ⋅ (C Pu − 236 − C 0, Pu − 236 ) APu − 236 ⋅ [C Pu − 238 − C 0, Pu − 238 − CT , Pu − 238 ] M ⋅ (C Pu − 236 − C 0, Pu − 236 ) specific activity or concentration of Pu-239+240, in Bq/g or Bq/l specific activity or concentration of Pu-238, in Bq/g or Bq/l amount of sample taken for analysis, in g or l count rate in the Pu-239+240-peak, in s-1 background count rate in the Pu-239+240-peak, in s-1 count rate in the Pu-238-peak, in s-1 background count rate in the Pu-238-peak, in s-1 count rate in the Pu-236-peak, in s-1 background count rate in the Pu-236-peak, in s-1 background in the Pu-239+240-Peak, in s-1 (count rate, which is not produced by the decay of Pu-239+240, but is a consequence of peak tailing) background from peak tailing in the Pu-238-Peak, in s-1 background from peak tailing in the Pu-236-Peak, in s-1 activity of Pu-236, added for yield determination, in Bq 3-1-5-3 Calculation of the standard deviation; The standard deviations of the plutonium activities are obtained with the following equations: 2 s D , Pu − 239+ 240 APu − 236 C Pu − 239+ 240 C 0, Pu − 239+ 240 C T , Pu − 239 + 240 C n , Pu − 239 + 240 C Pu − 236 C 0, Pu − 236 ⋅ = ⋅ + + + + C t M ⋅ C n , Pu − 236 tM t0 tM t0 n , Pu − 236 M 49 2 s D , Pu − 238 APu − 236 C Pu − 238 C 0, Pu − 238 CT , Pu − 238 C n , Pu − 238 C Pu − 236 C 0, Pu − 236 ⋅ = ⋅ + + + + M ⋅ C n , Pu − 236 tM t0 tM t0 C n , Pu − 236 t M where: sD,Pu-239+240 sD,Pu-238 Cn,Pu-239+240 Cn,Pu-238 tM t0 standard deviation of the Pu-239+240 specific activity or concentration, in Bq/g or Bq/l standard deviation of the Pu-238 specific activity or concentration, in Bq/g or Bq/l net count rate in the Pu-239+240-Peak net count rate in the Pu-238-Peak time of measurement of the sample, in s time of measurement of the background, in s 3-1-5-4 Calculation of the lower limit of detection (according to German standard DIN 25 482) , D Pu − 239 + 240 = , D Pu − 238 = (k 1−α + k1− β ) ⋅ APu − 236 M ⋅ C n , Pu − 236 ( k1−α + k 1− β ) ⋅ APu − 236 M ⋅ C n, Pu − 236 ⋅ C 0, Pu − 239 + 240 t M ⋅ 1 + tM t0 ⋅ C 0, Pu − 238 t M ⋅ 1 + tM t0 C T , Pu − 239 + 240 + tM C T , Pu − 238 + tM where: k1-α Quantil of the Gaussian distribution for errors of 1st order (preselect risk for concluding falsely that activity is present) k1-β Quantil of the Gaussian distribution for errors of 2nd order (predetermined degree of confidence for detecting the presence of activity) DIN 25 482-1 recommends for the errors of 1st and 2nd order a probability of 0.05. This means that k1-α = k1-β = 1.645 at the 95 % confidence level. The alpha-spectra of blank samples very often show more counts than background measurements of clean stainless steel disk. This means that the analytical procedure is not able to separate other alpha emitting nuclides completely. To minimize the risk that you falsely conclude that activity is present, it is advisable to preselect an error probability of 0.0014 for errors of 1st order. This means that k1-α = 3.000. 50 3-1-5-5 Calculation of the limit of decision The limits of decision DPu-239+240, and DPu-238and can be calculated with the following equations: D Pu − 239 + 240 = D Pu − 238 = k1−α ⋅ APu − 236 C 0, Pu − 239 + 240 ⋅ S ⋅ C n , Pu − 236 tM k 1−α ⋅ APu − 236 C 0, Pu − 238 ⋅ S ⋅ C n , Pu − 236 tM t ⋅ 1 + M t0 t ⋅ 1 + M t0 C T , Pu − 239 + 240 + tM C T , Pu − 238 C T , Pu − 236 + + tM tM 3-1-6 Quality Control Quality control measurements are necessary to provide documentation to show the reliability of the achieved results. The results reliability is a function of precision (reproducibility) and accuracy (the closeness to the true value). Precision can easily be determined by additional internal determinations. The accuracy of the results can be determined through performing control analysis with reference materials that are as similar as possible to the analyzed material samples, and through participating in intercomparison and/or proficiency measurements at least once per year. After performing 10-12 assays, a blank has to be performed with the same equipment and the same chemicals to ensure that there is no cross contamination. A blank is always recommended when samples with high plutonium content have been analyzed or when there are symptoms for a contamination of the laboratory, the equipment, or the chemicals. The status of the equipment should be checked routinely by measuring background, blanks and standards. These results often give the first indication of analytical difficulties. Analytical control samples generally constitute about 10-15 % of the total samples. 51 3-1-7 References: • R. Winkler, E. Frenzel, H. Rühle, J. Steiner: Schnellmethoden zur Analyse von Plutonium und anderen Aktiniden in Umweltproben. Publikationsreihe Fortschritte im Strahlenschutz, FS-90-51-AKU, Verlag TÜV Rheinland, Köln 1991 • Meßanleitungen für die Überwachung der Radioaktivität in der Umwelt und zur Erfassung radioaktiver Emissionen aus kerntechnischen Anlagen (Herausgeber: Der Bundesminister für Umwelt, Naturschutz und Reaktorsicherheit), Gustav Fischer Verlag, Stuttgart, Jena, New York 1995 • E. Holm: Review of Alpha-Particle Spectrometry Measurements of Actinides.Int. J. Appl. Radiat. Isot. 35, 285-290 (1984) • O. Frindik: Alphaspektrometrische Methode zur Bestimmung von Plutonium und Uran in Lebensmitteln, biologischem Material und Böden. BFE-Bericht 1980/6, Karlsruhe 1980 • Pimpl M., Schüttelkopf H. The measurement of Pu in Environmental Samples and in Gaseous and Liquid Effluents of Nuclear Installations. In: Proc. 1st Intern. Contact Seminar in Radioecology, Report SLU-REK-61, Uppsalla,1986. • Pimpl M., Schüttelkopf H.. A Fast Radiochemical Procedure to measure Np, Pu, Am, and Cm in Environmental Samples for Application in Environmental Monitoring and Radioecological Research. 5th Intern. Conf. On Nuclear Methods in Environmental and Energy Research, Mayaguez, Puerto Rico, April 2-6, 1984. • Winkler R., Frenzel E., Rühle H., Steiner J. Rapid Methods for the Analysis of Plutonium and Other Actinides in Environmental Samples. Report FS-90-51-AKU, Verlag TÜV Rheinland, Köln, 1991. • R.H. Higgy and M. Pimpl. Natural and Man-Made Radioactivity in Soils and Plants around the Research Reactor of Inshass. Appl. Radiat. Isot., 49, p. 1709-1712, 1998. International Congress Series 1276 (2005) 405 – 406 www.ics-elsevier.com Distribution pattern of natural radionuclides in Lake Nasser bottom sediments Ashraf E. Khatera,*, Yasser Y. Ebaidb, Sayed A. El-Mongya a National Center for Nuclear Safety and Radiation Control, Atomic Energy Authority, Egypt b Physics Department, Faculty of Science, Fayum, Cairo University, Egypt Abstract. In Egypt, the Nile River water is the main source of water, providing nearly 95% of water requirements. The Nile water is impounded in Lake Nasser (LN) in the south of Egypt by the High Aswan Dam (HAD). In this study, we presented the radioactivity levels in LN sediments over the time period 1992–2000 and the distribution pattern of the measured radionuclides (238U series, 232Th series, 40 K and 137Cs). In addition, the uranium concentration in water samples was measured. The distribution pattern of these radionuclides in sediments reflects the geochemical behavior and weathering processes of uranium series, thorium series and the heavy minerals in the Nile pathway and in Nasser Lake. D 2004 Published by Elsevier B.V. Keywords: Natural radioactivity; Nasser Lake; Sediment; Uranium; Laser flourimetry; Polonium 1. Introduction Since the construction of High Aswan Dam (HAD) in 1964, a large reservoir, Lake Nasser (LN), has been formed at the dam’s upstream side. The reservoir length is calculated to be approximately 500 km; accordingly, the largest surface area and maximum storage capacity of the reservoir are estimated at 600 and 162 km3, respectively [1]. This study aims at monitoring the radioactivity levels in the lake sediment and water, and to investigate the distribution pattern of different radionuclides in the lake sediments. 2. Experimental techniques During four sampling trips (1992–2000), 84 bottom sediment samples and 18 surface water samples were collected from Lake Nasser. The collected sediment samples were prepared and sealed in polyethylene containers to reach secular equilibrium between * Corresponding author. Present address: Physics Department, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Kingdom of Saudi Arabia. Tel.: +966 50 241 8292; fax: +966 146 76 448. E-mail address: khater _ [email protected] (A.E. Khater). 0531-5131/ D 2004 Published by Elsevier B.V. doi:10.1016/j.ics.2004.11.112 406 A.E. Khater et al. / International Congress Series 1276 (2005) 405–406 Table 1 Mean specific activity of U-238 (Ra-226) series, Th-232 (Ra-228) series, K-40 and Cs-137 (Bq/kg) and activity ratio of Ra-226/ Ra-228 in Nasser Lake sediments Ra-226/Ra-228 0.85F0.05 0.83F0.05 0.96F0.07 0.77F0.02 – a (0.19, (0.27, (0.31, (0.11, 12) 24) 20) 21) Cs-137FE K-40FE 7.6F0.8 (2.6, 11) 4.5F0.5 (2.4, 19) 5.25F0.5 (2.2, 20) 2.3F0.3 (1.3, 18) 8.9F0.6 309.1F12.1 221.6F17.0 326.2F16.4 317.6F18.1 310F4.3 (420, 12) (99.8, 25) (73.3, 20) (82.7, 21) Ra-228FE Ra-226FE 19.4F1.4 20.9F2.6 24.4F2.0 18.4F1.1 24.8F0.8 15.7F0.6a (2.06, 12) 15.3F1.6 (7.9, 25) 22.0F1.8 (8.1, 20) 14.3F1.1 (4.8, 21) 19.1F0.4 (4.4, 12) (12.5, 24) (9.1, 20) (5.2, 21) 1992 1998 1999 2000 [4] Mean valueFstandard error (standard deviation, number of samples). Fig. 1. Longitudinal profile of Ra-226, Ra-228, Pb-210, K-40 and Cs-137 (Bq/kg) in Lake Nasser sediments and U-238 (mBq/l) in water. radium and thorium and their progenies [2]. Gamma spectrometer based on hyper pure germanium detector and uranium analyzer of model Sintrex UA-3 were used for radioactivity measurements of sediment and water samples [2,3]. 3. Results and discussion The mean specific activity of 238U (226Ra) series, 232Th series, 40K and 137Cs in Bq/kg dry weight of sediment and activity ratio of 226Ra/228Ra in Lake Nasser sediments are given in Table 1. Longitudinal profile of 226Ra, 228Ra, 40K and 137Cs (Bq/kg) in Lake Nasser sediments and 238U (mBq/l) in water are shown in Fig. 1. The average concentration of uranium in the lake’s water is 3.26 mBq/l, which is comparable to that in the purified Nile River water in Cairo (3.47 mBq/l) and less than that in the purified Nile water in other northern Cities (5.7–9.2 mBq/l) [5]. References [1] [2] [3] [4] [5] M.S. El-Manadely, et al., Lake Reserv. Res. Manage. 7 (2002) 81 – 86. A.J. Khater, Environ. Radioact. 71 (2004) 33 – 41. H. Diab, M. El-Tahawy, S. El-Mongy, Radiochim. Acta 89 (2001) 179 – 185. S.S. Ismail, E. Unfied, F. Grass, Radioanal. Nucl. Chem. Lett. 186 (2) (1994) 143 – 155. M.S. El-Tahawy, S.A.M. El-Mongy, S.Y. Omar, Isotopes Radiat. Res. 27 (2) (1995) 95 – 101. IAEA-CN-98/5/06P DETERMINATION OF 238PU AND 239+240PU BY DESTRUCTIVE ASSAY TECHNIQUE A.E.M. KHATER, Y.Y. EBAID, S. EL-MONGY, M.S. EL-TAHAWY National Center for Nuclear Safety and Radiation Control, Atomic Energy Authority, Cairo, Egypt Abstract. Analysis of plutonium in environmental samples is one of the recent measures of the international safeguards. Plutonium with some other actinides, and fission and activation products in environmental samples are currently used as indication of undeclared nuclear activities. This work presents two destructive assay (DA) procedures for determination of 238PU and 239+240PU in environmental samples. Alpha spectrometers were utilized to identify the isotopic composition of Pu in the samples. The results show coincidence of the determined Pu concentration with the certified values. U-test was used as a quality control indicator of the presented procedures and results. The concentration levels of 238PU and 239+240PU in the analyzed samples ranged from 1.6 x 107 to 4.2 x 108 atoms, and from 2.2 x 1010 to 2.6 x 1011atoms respectively. Both methods could be applied for accurate low-level analysis to indicate plutonium origin. Introduction In the framework of the modern approaches of the international community to strengthen the non-proliferation measures, analysis of environmental samples by destructive (DA) and nondestructive (NDA) techniques is going to be used for discovery of undeclared nuclear activities [1&2]. The problem of accurately detecting of extremely low level of Pu is gaining increased importance in application of nuclear counter-proliferation, verification, and environmental and waste management. The sources of Pu isotopes in the nature are the atmospheric nuclear weapons testing, the re-entry burn up of a 238Pu auxiliary powered navigational satellite (SNAP-9A), the nuclear fuel reprocessing plants, nuclear accident and the nuclear reactor effluents. Discrimination between different sources of anthropogenic Pu requires both precise and accurate isotopic ratio determination at environmental levels [3]. The earth crust and its surface contain only negligible quantities of natural Pu [4]. In the environment, the mean specific activity of man-made 239Pu isotope is very close to 10 -13 g/g (0.23 mBq/g) for the surface soil. In some places, nuclear weapon testing sites, Pu producing nuclear reactor sites and close to the chemical factories of Pu extraction from nuclear fuel element, the specific activity of Pu can exceed the normal level by a factor greater than 10 2 [5]. Observation of any significant changes in the isotopic ratio of plutonium; 238Pu/239+240Pu, can probably indicate the presence of material from sources other than the global fallout. Whereas the activity ratio 238Pu/239+240Pu due to the fallout of weapons tests and the burning of the power supplies of satellites was 0.081, the ratios in the discharges of nuclear installations were up to 2.4 [6]. The 241Pu/239+240Pu activity ratio varies very much depending on the origin of plutonium isotopes. For Fresh fallout from nuclear weapon tests, this activity ratio is about 12-16, while for spent nuclear fuel from power reactor it is about 130 [5]. 1 Ashed sample material add yield tracer Pu-236 leaching with 8 M HNO3 / 0.9 M HF leaching with 5 M HNO3/ 1 M Al(NO3)3 add NaNO2, filtrate Dissolved Sample Material Extraction with TOPO/ Cyclohexane Aqueous Phase: discard Organic Phase: wash 3 times with 3 M HCl Back-extraction with 0.5 M Ascorbic Acid/1 M HCl Organic Phase: discard Aqueous Phase: wash 3 times with CHCl3 Coprecipitation with LaF3 wash precipitation with 1.5 M HF dissolve H3BO3 (saturated)/HNO3 (65%) add NaNO2 Dowex 1x2, 50 - 100 mesh Anion-Exchange wash with 7.2 M HNO3 wash with 9 M HCl eluate with 0.36 M Hcl/0.01 M HF evaporate to dryness dissolve with 4 M HCl add (NH4)2C2O4 (4%) Electro-deposition Alpha-Spectrometry Fig. (1): Flow chart illustrating the basic elements of the radiochemical procedure for plutonium analysis (LLE). Ashed sample material add yield tracer Pu-242 Totally dissolved with HNO3, HF, HCl and H3BO3 Dissolved Sample Material Anion-Exchange Dowex 1x2, 50 -100 mesh wash with 7.2 M HNO3 wash with 9 M HCl eluate with NH4I/1M HCl evaporate to dryness dissolve with 0.1 M HCl add (NH4)2C2O4 (4%) 1 Amp current applied for 30 min Electro-deposition Alpha-Spectrometry Fig. (2): Flow chart illustrating the basic elements of the radiochemical procedure for plutonium analysis (IEC). 2 The objective of this work is to study the convenience of two destructive procedures for plutonium isotopic composition analysis of different sample types. Description of the Procedures Two radiochemical analysis procedures for plutonium isotopes (238Pu and 239+240Pu) analysis have been investigated as for their convenience. Flow charts of the two procedures are given in figs. 1 and 2. Determination of Pu in environmental samples by alpha spectrometry involves tedious radiochemical procedure to separate this radionuclide from the matrix. The first step in Pu isotopes separation from the matrix is the conversion of the Pu into acid soluble form. For Pu activity concentration and chemical yield determination, 236Pu or 242Pu was used as internal tracer. In the first procedure (LLE), Pu isotopes were quantitatively converted into acid soluble form by leaching from the 100 g ashed samples in two steps with HNO3/HF and HNO3/Al(NO3)3 solutions. While, the second procedure (IEC), the 10g ashed samples were totally dissolved with HNO3, HF and HCl acids. In LLE procedure, Pu was separated from most of the matrix elements by extraction with TOPO/Cyclohexa and back extraction with HCl/Ascorbic acid. Then, the Pu fraction was purified radio-chemically by coprecipitation with LaF3 and anion exchange chromatography. While, in IEC procedure, Pu was separated from most of the matrix element and purified using ion exchange chromatography. The concentration of the alpha 238PU and 239+240PU were measured using alpha spectrometers after electroplating in Oxalate/HCl medium [7,8]. For determination of plutonium isotopes activity concentration and their ratio, the electroplated disks were measured using alpha spectrometers based on passivated implanted planar silicon (PIPS) detectors with 450 mm2 surface area and about 25 % efficiency and about 20 keV resolution at 4.41 MeV of 241Am was used. The detector was calibrated by using mixed standard source containing 239Pu, 241Am and 244Cm. The samples were measured for 60000 - 80000 second. Both of them have been tested against standard reference materials and certified samples to estimate the accuracy and reliability of the results. The accuracy of the results was evaluated using the u-test [9]. Results and Discussion The results of 238Pu and 239+240Pu obtained by LLE and IEC procedures are given in tables 1 and 2, respectively. The concentration levels of 238PU and 239+240PU in the analyzed samples ranged from 1.56.107 to 4.24.108 atoms (from 3.92 to 106.0 mBq/g), and from 2.2.1010 to 2.6.1011 atoms (from 20.3 to 236.0 mBq/g), respectively. The results were evaluated using the U-test score as given in the following equation [9] and the physical meaning of the u score value is given in Table 3. U test = ValueIAEA − ValueAnalyst Unc.2IAEA + Unc.2Analyst 3 Table 1. Quality control data for reference and certified samples analyzed using LLE procedure and alpha spectrometry for plutonium isotopes. 238 239+240 Pu Pu Comments Sample code Certified (mBq.g-1) Measured (mBq.g-1) U-test Certified (mBq.g-1) Measured (mBq.g-1) U-test IAEA-384 39.0± 1.1 35.4 ± 2.3 2.5 108 ± 2.5 100.5 ± 6.3 1.11 Accepted 1.66 Accepted 0.41 Accepted 0.02 Accepted Sediment SOIL-131* (1.41.108 atom) 35.9 ±0.7 34.0± 3.0 (1.1.1014 atom) 0.61 77.0± 1.6 8 10 (7.4.10 atom) (1.36.10 atom) Standard 114.0 ±2.3 Sol. 134 106.0 ± 9.0 0.86 244.0+4.9 (2.6.10 atom) (4.24.10 atom) - - 236.0+18.0 11 8 Standard 68.0± 5.0 - 191.0+3.8 190.0+4.3 11 Sol. 635 (2.1.10 atom) * mBq/Sample 1 Bq 239 Pu = 1.09x10 12 atoms, 1 Bq 238 Pu = 3.99x109 atoms Table 2. Quality control data for certified soil samples analyzed using IEC procedure and alpha spectrometry for plutonium isotopes. 238 239+240 Pu Pu Comments Sample code Certified (mBq.g-1) Measured (mBq.g-1) U-test Certified (mBq.g-1) Measured (mBq.g-1) U-test 00.38894 3.81 ± 0.15. 3.92 ± 0.31 0.3 25.90 ± 0.74 25.70 ± 1.33 0.1 Accepted 0.5 Accepted 0.03 Accepted 7 10 (2.8.10 atom) (1.56.10 atom) 00.38890 11.47 ± 0.37 12.16 ± 0.56 1.0 22.20 ± 0.74 (4.85.107 atom) 00.32154 20.72 ± 0.70 18.5 ± 0.78 23.03 ± 0.96 (2.5.1010 atom) 2.1 20.35 ± 0.63 7 20.32 ± 0.84 10 (2.2.10 atom) (7.38.10 atom) Table 3. Physical Meaning of the U –Test Score Value. Condition u<1.64 Probability Greater than 0.1 1.95>u>1.64 Between 0.1 and 0.05 2.58>u>1.95 Between 0.05 and 0.01 3.29>u>2.58 Between 0.01 and 0.001 u>3.29 Less than 0.001 4 Status The reported result does not differ significantly from expected value The reported result probably does not differ significantly from expected value It is not clear whether the reported result differ significantly from expected value The reported result is probably significantly different from the expected value The reported result significantly differs from expected value Regarding the samples preparation (double leaching with HNO3/HF and HNO3/Al(NO3)3 , and total sample dissolution), it was noted that both of them showed results that passed the Utest which means that both of them have succeeded to bring the refractory compounds of plutonium in the reference samples into an acid soluble form [10]. In regards to the time needed for analysis, namely a batch of four samples, the LLE procedure showed a shorter time for analysis. However, for larger batches (up-to-18 samples) the IEC procedure showed better performance. The LLE procedure results in a mixed organic radioactive waste while the IEC procedure produces only an aqueous radioactive waste, which is easier in handling from the waste management point of view. The lower limits of detection obtained by the LLE and IEC procedures are 1.0 and 0.74 mBq/sample (3.99 x 106 and 2.9 x 106 atoms for 238Pu, and 1.09x 109 and 8.1x 108 atoms for 239Pu) respectively. Lower Limits of detection, as low as 2.9 x 103 atoms for 238Pu, could be reached depending on the procedure parameters such as sample size and counting time. CONCLUSIONS It was observed that the analysis of plutonium isotopic composition in environmental samples by the presented destructive assay procedures are very promising and fulfil the requirement of the recent approaches of the international safeguards. As low as 3.99 x 104 and 2.9 x 105 atoms of 238Pu and 1.09x 107 and 8.1x 107 of 239Pu for LLE and IEC procedures respectively could be obtained. The presented procedures could also be used for swipe sample analyses. Development of the procedure to reach lower detection limit of Pu is an on-going activity. REFERENCES [1] Andrew, G.: Prospects for Environmental Monitoring in International Safeguards. London, United Kingdom (1994). [2] The Additional Protocol to the NPT (INFCIRC/540), IAEA, Vienna , Austria , 1997 [3] Linsalata P., Wrenn M.E., Cohen N., and Singh N.P. Pu-239+240 and Pu-238 in sediment of the Hudson River Estuary. American Chemical Society 14 (2), 1519-1523 (1980). [4] Pimpl M. and Scuettelkopf H. The measurement of Pu in Environmental samples and in Gaseous and liquid effluents of nuclear installations. Swedish University of Agricultural Sciences, Uppsala. Report SLU-REC-61, 53-62 (1986). [5] Hakanen, M., Jaakola, T. and Korpela, H. 1984 “ Simoultineous determination of 241Pu, 238 Pu and 239+240Pu in low activity environmental samples. Nucl. Instrum. Methods Phys. Res. 223, 382-383. [6] Holgye, z., Filgas, F. and peskova, V. 1989 “ Results of three Years of Monitoring 239+240 Pu and 238Puconcentrations in airborne effluents from the V-1 nuclear power plant with VVER 440reactors in Jaslovske Bohunice in Czechoslovakia. J. Radioanal. Nucl. Chem. Lett. 17, 135, (1989). [7] Strezov, A., Yordanova, I., Pimpl, M. and Stoilova. Natural radionuclide and plutonium content in Black Sea bottom sediments. Health Physics, Vol. 70 (1), 70-80, (1996). 5 [8] Peters, R. J., Knab, D., Eberhardt, W. Plutonium in Soil and Water Samples-Alpha Spectrometry” Method No. ER160, Health and Environmental Chemistry Analytical Techniques, Data Management, and Quality Assurance, LA-10300-M, Vol. II Manual, Los Alamos National Laboratory, (1984). [9] Brookes, C.J. Bettekey, I. G., and Loxton, S. M., 1979 “Fundamentals of Mathematics and Statistics” Wiley, New York, (1979). [10] UNSCEAR: United Nations Scientific Committee on the Effect of Atomic Radiation, Report to the General Assembly, (1982). 6 224 Int. J. Low Radiation, Vol. 3, Nos. 2/3, 2006 Polonium-210 in cigarette tobacco Ashraf E.M. Khater* National Center for Nuclear Safety and Radiation Control Atomic Energy Authority P.O. Box 7551, Nasr City, Cairo 11762, Egypt E-mail: [email protected] *Corresponding author Physics Department, College of Science King Saud University P.O. Box 2455, Riyadh 11451 Kingdom of Saudi Arabia Hamed A.I. Al-Sewaidan Physics Department, College of Science King Saud University P.O. Box 2455, Riyadh 11451 Kingdom of Saudi Arabia E-mail: [email protected] Abstract: Tobacco and tobacco smoke contain minute amounts of some natural radionuclides such as 210Pb and 210Po, which are carcinogens. Intake of these radionuclides results in an increase of radiation doses to lung cells and tissues. Samples of the most frequently smoked cigarette brands were collected from the local market of Riyadh City, Saudi Arabia. Activity concentrations of 210 Po were measured by alpha spectrometers, following the radiochemical separation of polonium. The average activity concentration (range) of 210Po was 15.1 (5.5–22.2) mBq/cigarette. Cigarette smokers who consume one pack (20 cigarettes) per day are inhaling an average of 151 mBq/day of 210Po and 210Pb each. The mean values of the annual effective dose for smokers (one pack per day) were estimated to be 237 and 309 µSv from 210Po and 210Pb, respectively. Keywords: cigarette smoking; lead-210; polonium-210; radiation dose; Saudi Arabia; tobacco. Reference to this paper should be made as follows: Khater, A.E.M. and Al-Sewaidan, H.A.I. (2006) ‘Polonium-210 in cigarette tobacco’, Int. J. Low Radiation, Vol. 3, Nos. 2/3, pp.224–233. Biographical notes: Ashraf Khater received his Doctorate in Medical Biophysics at Cairo University in 1998. He is Assistant Professor in the Physics Department of King Saud University. He began his scientific career at the Egyptian Atomic Energy Authority, where he conducted research from 1986 to 2003. His research focuses on environmental radioactivity studies. He has experience in the fields of low-level radioactivity measurements and radiochemical separation and measurement of actinides. Since 2002, he has been a qualified radiation protection expert in Egypt. He has published about 20 research papers in the field of environmental radioactivity and radiation measurements. Copyright © 2006 Inderscience Enterprises Ltd. Polonium-210 in cigarette tobacco 225 Hamed Al-Sewaidan is Assistant Professor of Physics at King Saud University (KSU), Riyadh, Saudi Arabia. He obtained his BSc in Physics in 1980 and worked as Demonstrator at the same university for several years. Later, he obtained his MSc and PhD from Birmingham University, UK, and the University College of Wales, Swansea, UK, respectively. Since 1991, he has been conducting research at KSU mainly in the fields of radiation physics and biophysics. In addition, he has taught many subjects areas in physics for both undergraduate and postgraduate students, while continually supervising the research work of his students. 1 Introduction A large body of medical research indicates that tobacco smoking has serious consequences for human health. Chronic smokers run the risk of lung cancer, respiratory infections, heart disease and other health complications. The annual worldwide mortality due to tobacco use is estimated at 3 million. Cigarette Mainstream Smoke (MS) is a complex aerosol consisting of a vapour and a particulate phase. The particles range from 0.1 to 1 µm in diameter (average 0.2 µm) and undergo very rapid coagulation, resulting in mean diameter increases (Dhar, 2004; Smith and Fischer, 2001). Since the 1960s, studies have suggested that the two radionuclides present in tobacco – lead-210 and polonium-210 (decay products of radon gas) – might promote cancer when deposited in lungs. Lead and polonium were believed to enter tobacco as airborne fallout on the leaves and as natural contaminants of phosphate fertilizers absorbed through tobacco roots (Tso et al., 1964; Tso et al., 1966). Polonium-210, which has a physical half-life of 138 days, is a member of the natural uranium-238 series and one of the relatively long-lived radionuclides of radon decay products. It is an alpha emitting radionuclide and is present in trace amounts in most plants and foodstuffs as well as in human tissues. The polonium isotopes are among the most radiotoxic nuclides to human beings (Batarekh and Teherani, 1987). The concentrations of 210Po in cigarette tobacco are in the range of 2.8–37 Bq/kg and vary with the cigarette brand due to the different varieties of tobacco used and different manufacturing procedures (Skwarzec et al., 2001a). The results obtained by Radford and Hunt (1964) indicate that 210Po in cigarettes is volatilised at temperatures from 600°C to 800°C. This range is characteristic of burning cigarettes and inhaled into the lungs along with the cigarette smoke (mainstream smoke). It might effectively be a factor in the increased incidence of lung cancer among cigarettes smokers (Radford and Hunt, 1964). Lead-210 is not sublimated at this temperature but is rather a component of the resulting smoke and ash (Watson, 1985). Lead is inhaled with the particulate fraction of mainstream smoke and acts as a long-term source of 210Po exposure. Numerous investigators have studied both the sources and behaviour of 210Po and 210Pb in relation to smoking and the biological effects of these on lung tissues and other organs (Batarekh and Teherani, 1987; Black and Brethauer, 1968; Boltzman and Ilcewicz, 1966; Cohen et al., 1979a; Cohen et al., 1979b; Fletcher, 1994; Godoy et al., 1992; Karali et al., 1996; Martell, 1974; Mussealo-Rauhammaa and Jaakkola, 1985; Nada et al., 1999; Rajewsky and Stahlhofen, 1966; Shabana et al., 2000; Sinh and Nilekani, 1976; Tso et al., 1964; Tso et al., 1966; Watson, 1985). 226 A.E.M. Khater and H.A.I. Al-Sewaidan About 6.5%–22% of the 210Po contained in cigarettes was found in mainstream smoke (Mussealo-Rauhammaa and Jaakkola, 1985; Radford and Hunt, 1964). Other authors have reported different percentage values, ranging from 3.7% to 58%. On average, approximately 50% of the 210Po in cigarette tobacco is transferred to the smoke, 35% remains in the butt and approximately 15% is found in the ash (Parfenov, 1974). Khater (2004) studied the quantitative distribution of 210Po in tobacco cigarette between the cigarette smoke and ash. It was concluded that the relatively low 210Po activity measured in the cigarette ash is due to the volatilisation of polonium at the cigarette burning temperature. On average, about 25% of the total polonium in cigarette tobacco was retained in the cigarette filter and ash, while the rest (i.e., 75% of the polonium content in cigarette tobacco) was contained in the cigarette smoke. Numerous variables govern the degree of exposure via the pathway tobacco smoke: the geographic region where the tobacco is grown, the fineness of the tobacco cut, the presence or absence of a filter, the size and composition of the filter and smoking habits (Watson, 1985). It has been reported that the content of other carcinogens in tobacco today has been greatly reduced by the changes in tobacco processing methods and the use of modern cigarette filters. However, these have little effect in terms of reducing radioactivity levels (Khater, 2004). This work was aimed at determining 210Po specific activity in most frequently smoked cigarettes in Saudi Arabia in order to estimate the annual effective dose to cigarettes smokers due to 210Po and 210Pb inhalation via smoking. 2 Experimental work Twenty-one samples of five different brands of most frequently smoked cigarettes in Saudi Arabia were randomly selected from those available on the local market of Riyadh City. Although each brand has several types of cigarettes, only the most popular one was chosen for analysis. Six cigarettes were taken from each pack to provide combined samples of cigarette tobacco. Samples of known weights (3.3–6.4 g) were spiked with 209 Po (Eα = 4.9 MeV) tracer in order to calculate the chemical recovery of polonium from the analysed samples after chemical treatment. The samples were dissolved in rounded flasks using three portions of a 50 ml HNO3 (65%) and evaporated to near dryness on a sand bath at a temperature of about 90°C. The sample residuals were treated with three portions of 10 ml HCl (32%) and evaporated to near dryness. Finally, the samples were transferred into 50 ml glass beakers and dissolved in 35 ml 0.5 M HCl. Polonium was spontaneously plated from the solution at temperatures between 80°C and 90°C onto rotating stainless steel disks fixed in a Teflon disk holder (Flynn, 1968; Hamilton and Smith, 1986). The plated disks were measured using alpha spectrometers (Alpha Analyst CANBERRA), employing PIPS detectors with efficiencies about 17% and an average resolution of 17 keV in 241Am alphas and connected to a computerised multi-channel analyser operating with Genie 2000 software (CANBERRA). The samples were measured for about 85 000 seconds. Minimum Detectable Activity (MDA), of 1 mBq, determined for the detection system and radiochemical procedures adopted in this study (Currie, 1968). The average chemical recovery was 75%, and the individual values ranged from 50% to 100%. Analytical quality control measurements were Polonium-210 in cigarette tobacco 227 regularly performed through reference samples analyses, blank samples analyses and participation in IAEA inter-comparison exercises. The uncertainties of the reported results are evaluated considering counting statistics and calibration error only. 3 Results and discussions The activity concentration of 210Po, mBq/g and mBq/cigarette in five different cigarette brands, which were collected from the local market of Riyadh City, Saudi Arabia, are presented in Table 1. The mean, standard error, standard deviation, median and range of the activity concentration of 210Po, mBq/g and mBq/cigarette, in each of the five cigarette brands, their average and world average are presented in Table 2. The mean activity concentration of 210Po, mBq/g and mBq/cigarette, in each of the five cigarette brands, their average and world average are shown in Figure 1. The average activity concentration (range) of 210Po in cigarette tobacco was 15.1 (5.5–22.2) mBq/cigarette, which is comparable to the calculated world average (range), 14.5 (4.0–23.2) mBq/cigarette. The presented data shows a relatively wide range of activity concentration of 210Po in the different cigarette brands and even within the same brand. A probable reason for this is that all cigarette brands available in the local markets of Saudi Arabia are imported from different countries. Table 1 Specific radioactivity (mBq/g and mBq/cigarette) of 210Po in five brands of cigarettes from the local market of Saudi Arabia Serial number 1 Brand Sample code mBq/g ± E* mBq/Cig ± E A ME 1 16.13 ± 1.35 13.17 ± 1.10 2 ME 5 21.14 ± 2.04 11.98 ± 1.16 3 ME 7 15.88 ± 1.36 8.73 ± 0.75 4 ML 1 15.05 ± 1.41 13.30 ± 1.25 5 B ML 3 19.56 ± 1.56 17.93 ± 1.43 6 ML 5 22.48 ± 1.80 15.36 ± 1.23 7 ML 7 7.80 ± 0.81 5.46 ± 0.57 8 ML 9 20.60 ± 1.79 13.73 ± 1.20 MO 1 23.33 ± 2.12 22.16 ± 2.01 10 MO 3 19.74 ± 1.72 21.38 ± 1.87 11 MO 5 20.98 ± 2.66 14.69 ± 1.86 12 MO 7 25.90 ± 2.35 18.56 ± 1.68 9 Note: C *Only counting statistics and calibration error 228 Table 1 A.E.M. Khater and H.A.I. Al-Sewaidan Specific radioactivity (mBq/g and mBq/cigarette) of 210Po in five brands of cigarettes from the local market of Saudi Arabia (continued) Serial number Brand Sample code mBq/g ± E* mBq/Cig ± E D MR 1 20.95 ± 2.47 19.55 ± 2.30 14 MR 4 20.51 ± 2.04 19.15 ± 1.90 15 MR 10 20.28 ± 1.92 13.86 ± 1.31 16 MR 13 21.14 ± 2.19 14.45 ± 1.50 17 MR 7 18.43 ± 1.37 12.29 ± 0.91 RO 1 16.16 ± 1.96 13.73 ± 1.66 RO 3 25.15 ± 3.94 20.96 ± 3.28 13 18 E 19 20 RO 5 20.28 ± 1.84 12.17 ± 1.10 21 RO 7 24.47 ± 2.23 13.87 ± 1.26 Note: Table 2 Brand A B C D E All World average* Note: *Only counting statistics and calibration error Statistical summary of 210Po activity concentration, mBq/g and mBq/cigarette, in five brands of cigarettes from the local market of Saudi Arabia Number of samples 3 5 4 5 4 21 – Mean SE SD Median Range Unit 17.7 1.7 3.0 16.1 15.9–21.14 11.3 1.3 2.3 12.0 8.7–13.2 mBq/Cig 17.1 2.6 5.9 19.6 7.8–22.5 mBq/g 13.2 2.1 4.7 13.7 5.5–17.9 mBq/Cig 22.5 1.4 2.7 22.2 19.7–25.9 mBq/g 19.2 1.7 3.4 20.0 14.7–22.2 mBq/Cig 20.3 0.5 2.7 20.5 18.4–21.1 mBq/g 15.9 1.5 3.3 14.5 12.3–19.6 mBq/Cig 21.5 2.1 4.2 22.4 16.2–25.2 mBq/g 15.2 2.0 3.9 13.8 12.2–21.0 mBq/Cig 19.8 0.9 4.0 20.5 7.8–25.9 mBq/g 15.1 0.9 4.1 13.9 5.5–22.2 mBq/Cig 14.5 1.1 4.9 14.1 4–23.2 mBq/Cig *Based on the data presented in Table 3 mBq/g Polonium-210 in cigarette tobacco 229 Activity concentration of 210Po (Bq/g and mBq/cig.) in different cigarette brands from Saudi Arabia Figure 1 Po-210 activity concentration Bq/g mBq/Cig. 20 15 10 5 0 A B C D E e e erag rag Ave orld av W Cigarette brand Average activity concentrations for 210Po, mBq/cigarette, in cigarettes tobacco from Saudi Arabia and those from other countries are shown in Table 3 and Figure 2. These sets of data indicate that 210Po concentrations ranged from 3.3 mBq/g (about 4 mBq/cigarette, which is based on the normal value of cigarette weight of 1.2 g/cigarette) in Indian cigarettes to a maximum value of 23.2 mBq/cigarette in the French cigarettes. The average activity concentrations of 210Po in cigarette tobacco from Saudi Arabia and in those from other countries, expressed in mBq/cigarette Table 3 Country 210 Reference England 17.3 Black and Brethauer, 1968 Canada 7.9 Black and Brethauer, 1968 Egypt 14.1 Black and Brethauer, 1968 Po Finland 10.8 Black and Brethauer, 1968 Germany 19.2 Black and Brethauer, 1968 Japan 22.4 Black and Brethauer, 1968 Norway 8.6 Black and Brethauer, 1968 France 23.2 Black and Brethauer, 1968 Philippines 10.7 Black and Brethauer, 1968 Russia 14.1 Black and Brethauer, 1968 Turkey 14.3 Karali et al., 1996 Various 18.1 Parfenov, 1974 Notes: *In mBq/g Assuming 1.2 g tobacco per cigarette + 230 A.E.M. Khater and H.A.I. Al-Sewaidan The average activity concentrations of 210Po in cigarette tobacco from Saudi Arabia and in those from other countries, expressed in mBq/cigarette (continued) Table 3 Country 210 Reference Czechoslovakia 11.7 Parfenov, 1974 Brazil 16.9 Parfenov, 1974 Bulgaria 14.0 Parfenov, 1974 Finland 11.1 Mussalo-Rauhamaa and Jaakkola, 1985 Po 3.3* (3.96)+ India Poland 13.3 Sinh and Nilekani, 1976 Skwarzec et al., 2001c + Brazil 21.2* (25.4) Egypt 16.3 Egypt 21.0* Khater, 2004 Greece 10.5 Savidou et al., 2005 Saudi Arabia 15.1 This study Saudi Arabia 19.8* This study Notes: Peres and Hiromoto, 2002 Khater, 2004 *In mBq/g Assuming 1.2 g tobacco per cigarette + Activity concentration of different countries 210 Po, mBq/cigarette, in cigarette tobacco from 25 Po-210, mBq/Cig 20 15 10 5 0 En gl a C nd an ad a Eg y Fi pt nl G and er m an y Ja p No an rw a F y Ph ranc ilip e pi ne R s us si C ze T a ch urk os ey lo va kia Br az Bu il lg ar Fi ia nl an d In d Po ia la nd Br az Sa E il ud gyp iA t ra bi a Figure 2 Polonium-210 in cigarette tobacco 231 On account of the time interval between the harvesting of tobacco leaves and cigarette production (often more than two years ≅ about six half-lives of 210Po), 210Po in cigarette tobacco approaches a secular equilibrium with 210Pb (Godoy et al., 1992; Carvalho, 1995; Skwarzec et al., 2001b; Peres and Hiromoto, 2002). Activity concentration of 210Po (210Pb) in cigarette tobacco (mBq/cig.) and inhaled via smoking per day (mBq/d) and year (mBq/y) and annual committed effective dose (µSv/y) due to 210Po and 210Pb inhalation via smoking are shown in Table 4. Assuming that 50% of the total 210Po and 210Pb activity concentrations in cigarette smoke is inhaled during smoking (Skwarzec et al., 2001b), it means that for a smoker consuming one pack (20 cigarettes) per day, the average activity concentrations of both 210Po and 210Pb intake with cigarette smoke will thus be 152 mBq. This value may change depending on the number and size of puffs per cigarette (smoking habits) and the 210Po and 210Pb concentrations in the non-inhaled side smoke. By applying the dose conversion factor for adults of 5.6 µSv/Bq for 210Pb and 4.3 µSv/Bq for 210Po (Peres and Hiromoto, 2002; Savidou et al., 2005), the average annual committed effective dose is estimated to be 238.7 and 310.9 µSv due to cigarette smoking for 210Po and 210Pb, respectively, and 549.6 µSv due to inhalation of both 210Po and 210Pb in cigarette smoke. Average activity concentration of 210Po in cigarette tobacco, mBq/cig., and inhaled per day, mBq/d, and year, Bq/y, and annual committed effective dose, µSv/y, due to 210Po and 210Pb inhalation via smoking Table 4 210 Po(210Pb) activity concentration Brand Annual committed effective dose, µSv/y mBq/Cig. mBq/d Bq/y 210 210 Pbc Total A 11.3 113.0 41.3 177.5 231.1 408.6 B 13.2 131.6 48.1 206.7 269.2 475.9 C 19.2 192.0 70.1 301.6 392.7 694.3 D 15.9 159.0 58.1 249.7 325.2 574.9 E 15.2 152.0 55.5 238.7 310.9 549.6 All 15.1 151.0 55.2 237.2 308.9 546.0 14.5 145.0 53.0 227.7 296.6 524.3 World average Notes: a a 20 cigarette/day and 50% of b 210 Po ( Pob 210 Pb) in smoke inhaled. 210 4.3 µSv/Bq, Po dose conversion factor. Assuming 210 Po and 210Pb are in secular equilibrium and 210Pb dose conversion factor = 5.6 µSv/Bq. c Acknowledgements We wish to express our deep gratitude to Mr. M. Al-Husain of the Saudi Arabian Standards Organization for providing access to the alpha spectrometry system. The authors also acknowledge the financial support of the Research Center of the College of Sciences- King Saud University, Project No. phys/2005/05. 232 A.E.M. Khater and H.A.I. Al-Sewaidan References Batarekh, K. and Teherani, D.K. (1987) ‘Determination of polonium-210 in cigarettes from Syria’, Journal of Radioanalytical, Nuclear chemistry, Letters, Vol. 117, No. 2, pp.75–80. Black, S.C. and Brethauer, E.W. (1968) ‘Polonium-210 in tobacco’, Radiological Health Data and Report, pp.145–152. Boltzman, R.B. and Ilcewicz, F.H. (1966) ‘Lead-210 and polonium-210 in tissue of cigarette smokers’, Science, Vol. 153, pp.1259–1260. Carvalho, F.P. (1995) ‘210Po and 210Pb in take by Portuguese’s population: the concentration of seafood in the dietary intake of 210Po and 210Pb’, Health Physics, Vol. 69, pp.469–480. Cohen, B.S., Eisenbud, M. and Harley, N.H. (1979a) ‘Alpha radioactivity in cigarette smokes’, Radiation Research, Vol. 83, pp.190–196. 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(2005) ‘Concentration levels of 210Pb and 210Po in dry tobacco leaves in Greece’, Journal of Environmental Radioactivity, in press, www.sciencedirect.com. Polonium-210 in cigarette tobacco 233 Shabana, E.I., Abd Elaziz, M.A., Al-Arifi, M.N., Al-Dhwailie, A.A. and Al-Bokari, M.M. (2000) ‘Evaluation of the contribution of smoking to total blood Polonium-210 in Saudi population’, Applied Radiation and Isotopes, Vol. 52, pp.23–26. Sinh, D.R. and Nilekani, S.R. (1976) ‘Measurement of polonium activity in Indian tobacco’, Health Physics, Vol. 31, pp.393–394. Skwarzec, B., Struminska, D.I., Ulatowski, J. and Golebiowski, M. (2001a) ‘Determination and distribution of 210Po in tobacco plants from Poland’, Journal of Radioanalytical and Nuclear Chemistry, Vol. 250, No. 2, pp.319–322. Skwarzec, B., Ulatowski, J., Struminska, D.I. and Borylo, A. (2001b) ‘Inhalation of 210Po and 210 Pb from cigarette smoking in Poland’, Journal of Environmental Radioactivity, Vol. 57, pp.221–230. Skwarzec, B., Struminska, D.I., Borylo, A. and Ulatowski, J. (2001c) ‘Polonium 210Po in cigarettes produced in Poland’, J. Environ. Sci. Health, Vol. A36, No. 4, pp.465–474. Smith, C.J. and Fischer, T.H. (2001) ‘Particulate and vapor phase constituents of cigarette mainstream smoke and risk of myocardial infarction’, Atherosclerosis, Vol. 158, pp.257–267. Tso, T.C., Hallden, N.A. and Alexander, L.T. (1964) ‘Radium-226 and polonium-210 in leaf tobacco and tobacco soil’, Science, Vol. 146, pp.1043–1045. Tso, T.C., Harley, N. and Alexander, L.T. (1966) ‘Source of lead-210 and polonium-210 in tobacco’, Science, Vol. 153, pp.880–882. Watson, A.P. (1985) ‘Polonium-210 and lead-210 in food and tobacco products: transfer parameters and normal exposure and dose’, Nuclear Safety, Vol. 26, No. 2, pp.179–191. Lead-210 Specific Activity in Fish and Dose Assessment Ashraf E. M. Khater National Center for Nuclear Safety and Radiation Control, Atomic Energy Authority, P.O. Box 7551, Nasr City, Cairo 11762, Egypt. Email: [email protected] ABSTRACT Lead-210 is a member of uranium-238 series and has the longest half-live of radon-222 daughters. Fish samples of different species from two Egyptian Lakes (Bardawill and Qarun) were collected. Lead-210 activity concentration (Bq/kg dry weight) in fish muscle was determined through the measurement of Po-210 (daughter of Pb-210). Po-210 activity concentration was measured with alpha spectrometer after sample dissolution and platting of Po210 onto stainless steel disk from diluted HCl solution. Po-208 was used as a tracer for chemical yield determination. The chemical procedure of Po-210 is briefly described. Uranium series disequilibrium in fish muscle (Pb-210/Ra-226 activity ratio), distribution coefficient and absorbed dose via fish muscle consumption are calculated and discussed. Keyword: Lead-210, Fish, dose calculation, lake. INTRODUCTION Lead-210 (T =22.3 y), 210Bi (T1/2=5.01 d) and 210Po (T1/2 =138 d) are produced in the atmosphere by the decay of 222Rn (T1/2 = 3.82 d), which is the decay product of 226Ra (T1/2 = 1600 y). 210Pb and 210Po radionuclides are included in the group of most highly toxic radioisotopes and provide the major natural radiation dose due to internally deposited radionuclides[UNSCAER, 1988; Khater, 1997; Hameed, 1997]. 210Po and 210Pb enter the human body via inhalation of 222Rn (radon) gas and ingestion of food which is the major route of radionuclides intake. Studies on 210 Pb is particularly important because the metabolic properties of this radionuclides control the amounts of the daughters 210Bi and 210Po in the human and animal. Concerning the 210Po and 210 Pb intake via food consumption, the highest levels were observed in fish and sea-food (marine organisms) [Al-Masri, 2000; Cunha, 2001; Pietizak-Flis, 1997]. Since 1989, environmental monitoring program in Egypt have been implemented to set up the environmental radioactivity background data-base and to calculate the radiation dose due to natural radiation sources. The environmental radioactivity levels and the behavior of some natural radionuclides in the aquatic ecosystem of some Egyptian lakes were studied as a part of the Egyptian monitoring program. In this study, the natural (e.g. 238U series, 232Th series and 40K) and some artificial (e.g. 137Cs, 238Pu and 239+240Pu) radionuclides were measured in bottom and shore sediment, water and fish samples from three Egyptian lakes; namely Bardawill, Qarun and Edku lakes. The annual fish production of Bardawill and Qarun lakes are about 2500 tons (65 % Bream, 20 % Mullets, 6 % Sea-bass, 5 % Sole and 3 % others) and 956 tons, 1980-1990, (39 % Tilapias, 36 % Shrimps, 10 % Mullets, 10 % Sole, 2 % Sea-bass and 3 % others)[Khater 1997]. In the present work , in addition to brief reporting of the published data of 226Ra, 232Th and 40K specific activities (Bq/kg dry weight) in fish samples [Khater, 1997], the specific activity (Bq/kg dry weight) of 210Pb in selected fish muscle samples and the calculated annual individual effective dose (µSv/y) due to fish consumption have been evaluated. EXPERIMENT AND METHODS Fish samples were collected from the commercial collecting centers. The samples were washed with water to separate sand and any foreign materials. Depend on the fish species and size, the fish samples were filleted to have muscle and bone portions separately which were dried in an oven at 80 oC and crushed. The sample preparation and measurement of 226Ra, 232Th, 40K and 137 Cs using gamma spectrometers based on hyper pure Germanium detectors were described in our previous work [Khater, 1997]. Since the samples were collected four years ago, the measured 210 Po activity concentration is equivalent to 210Pb concentration in the sample. Up to 5 g of the dried samples were spiked, for chemical recovery and activity calculation, with about 80 mBq 208 Po, and dissolved using mineral acids (HNO3 and HCl). Finally the samples were dissolved in 30 ml 0.5 M HCl followed by the addition of ascorbic acid to reduce iron (III). Then, polonium was self-plated from the solution at temperatures 80 oC onto rotating stainless steel disk fixed in a Teflon disk holder [Hamilton and smith, 1986]. The plated disks were measured using alpha spectrometry (CANBERRA 4701 vacuum chambers) based on passivated implanted planar silicon (PIPS) detectors with 450 mm2 surface area, about 25 % efficiency and about 20 keV resolution, and connected up to a computerized multi-channel analyser operating with Genie 2000 software (CANBERRA). The samples were measured for 1000 min., applying a lower limit of detection of 1 mBq [Currie, 1968]. The average chemical recovery was 75 %, and the individual values ranged from 50 to 100%. The measured 210Po specific activity is equivalent to 210 Pb specific activity. RESULTS AND DISCUSSION: Specific activity (Bq/kg dry weight) of 226Ra, 232Th, 40K, 137Cs and 210Pb, and activity ratio of 210 Pb/226Ra in selected fish samples from Bardawill and Qarun lakes are given in table (1). The average specific activity ± standard error (range) of 210Pb in fish muscle samples from Baradwill and Qarun lakes were 1.82 ± 0.43 (0.32-5.78) and 0.49 ± 0.06 (0.32-0.70) Bq/kg dry weight respectively. The highest value in Bardawill and Qarun fish samples were observed in Mullets and Tilapias respectively. The average activity ratio ± standard error (range) of 210Pb/226Ra in fish muscle samples from Baradwill and Qarun lakes were 0.47 ± 0.10 (0.10-1.18) and 0.18 ± 0.04 (0.08-0.27) respectively. Although, it seems that the specific activity of 210Pb in Bream muscle is higher than in Mullet muscle in Bardawill lake samples. But the sample number is not large enough to have an obvious relationship between 210Pb specific activity and fish’s species which could be due to differences in metabolism and feeding patterns [Al-Masry, 2000]. Table 1: Specific activity (Bq/kg dry weight) of 226Ra, 232Th, 40K, 137Cs and 210Pb, and activity ratio of 210 Pb/226Ra in Bardawill and Qarun lakes fish samples. Ser. Species Sample* Ra-226 ± E Th-232 1 Bream B1 F 3.05 ± 0.49 1.48 2 Bream B11 F 2.98 3 Bream B13 F 3.76 4 Mullets B19 F 3.04 5 Mullets B20 F 3.24 ± E K-40 Pb-210 ± E Pb-210/ Ra-226 ± E Cs-137 ± E ± 0.36 288.2 ± 4.0 0.38 ± 0.17 1.06 ± 0.89 2.69 ± 0.73 324.8 ± 7.6 0.40 ± 0.31 2.24 ± 0.50 0.75 ± 0.70 1.50 ± 0.56 297.0 ± 3.5 <0.1 2.42 ± 0.41 0.64 ± 0.92 0.80 ± 0.33 632.4 ± 6.6 <0.1 3.25 ± 0.61 1.07 ± 1.14 1.81 ± 0.97 317.9 ± 8.0 0.49 ± 0.39 0.34 ± 0.16 0.10 Bardawill lake ± 0.57 0.35 6 Mullets B22 F 2.4 ± 1.44 0.64 ± 0.58 362.5 ± 12.1 <0.1 7 Bream B26 F 2.38 ± 0.81 1.57 ± 0.61 354.9 ± 6.8 0.32 8 Bream B34 F < 0.6 350.9 ± 9.8 < 0.1 9 Mullets B36 F 4.78 ± 1.08 2.48 ± 0.87 470.9 ± 7.6 0.58 ± 0.39 2.05 ± 0.65 0.43 10 Bream B37 F 4.67 ± 1.15 0.91 ± 0.43 135.4 ± 4.6 <0.1 0.72 ± 0.11 0.15 11 Bream B37HB 5.14 ± 1.57 4.73 ± 1.33 237.9 ± 0.8 1.37 ± 0.54 1.14 ± 0.28 0.22 12 Bream B38 F 3.30 ± 1.08 2.53 ± 1.40 229.2 ± 7.3 1.11 ± 0.68 0.62 ± 0.14 0.19 13 Bream B39 F 3.72 ± 0.67 1.59 ± 0.54 403.0 ± 4.2 < 0.1 14 Mullets B40 F 2.70 ± 0.46 1.90 ± 0.37 340.2 ± 4.0 15 Bream B41 F 3.10 ± 0.94 1.50 ± 0.54 303.4 16 Bream B41HB 6.06 ± 2.28 < 0.5 17 Bream B43 F 2.80 ± 2.45 1.00 1 Tilapias Q 4 FHB 2.63 ± 0.93 0.80 2 Tilapias Q 9 FHB 1.94 3 Tilapias Q29 FB 4.11 4 Sole 5 Mullets < 0.5 116.5 0.35 ± 0.15 0.15 ± 0.31 0.44 ± 0.20 0.18 5.78 ± 0.72 - 4.41 ± 0.44 1.18 0.50 ± 0.16 2.62 ± 0.40 0.97 ± 5.2 0.38 ± 0.37 0.32 ± 0.29 0.10 ± 9.3 < 0.1 0.70 ± 0.15 0.12 ± 12.3 0.99 ± 0.92 0.68 ± 0.28 0.24 ± 0.56 280.0 ± 7.0 0.22 ± 0.34 0.70 ± 0.21 0.27 ± 0.66 1.26 ± 0.63 247.8 ± 8.0 0.44 ± 0.31 0.51 ± 0.24 0.26 ± 0.76 1.75 ± 0.56 235.9 ± 4.3 0.4 ± 0.27 0.32 ± 0.11 0.08 Q 30 FHB 4.47 ± 1.28 0.61 ± 0.21 411.4 ± 8.2 < 0.1 0.46 ± 0.13 0.10 Q 35 FB ± 0.52 1.73 ± 0.39 353.8 ± 3.7 0.58 ± 0.17 0.43 ± 0.28 0.19 ± 0.65 426.9 Qarun Lake * F = muscle, 2.23 HB = Head and bone Average activity concentration of 226Ra, 232Th, 40K, 137Cs and 210Pb in bottom sediment, water and fish samples from Bardawill and Qarun Lakes were given in Table (2). In our previous study, we concluded that there is no obvious variation in 226Ra, 232Th and 137Cs specific activity with fish tissues and species. Although the highest activity concentration of 226Ra and 232Th, and 40K and 137Cs were measured in bone and muscle respectively. The average specific activity of 210Pb in Bardawill’s fish samples was higher than in Qarun’s fish samples, even in the same species. That could be due to the different in the chemical composition of water, where Barwaill’s water is highly saline (60 g/l) and the atmospheric flux of 210Pb in Bardawill lake is higher than in Qarun lake [Khater, 2000]. Table 2: Average activity concentration of 226Ra, 232Th, 40K, 137Cs and sediment, water and fish samples from Bardawill and Qarun Lakes. Lake Ra-226 ± E Bradawill Qarun 7.2 15.2 Bradawill Qarun Salinityx 60.5 <DL 32.4 <DL Bradawill [60]# Qarun [44] * Muscle F* B** F B ± 0.5 ± 0.2 3.3 4.3 2.9 3.6 ** Bone ± 0.2 ± 0.3 ± 0.6 ± 0.3 210 Pb in bottom Th-232 ± E K-40 ± E Cs-137 ± E Pb-210 ± E Bottom Sediment, Bq/kg dry weight 6.0 ± 0.6 205.5 ± 24.2 2.7 ± 0.02 21.3 ± 2.5 11.9 ± 0.5 255.3 ± 6.3 3.52 ± 0.2 25.2 ± 0.9 Water, Bq/l <DL 19.2 ± 0.9 <DL <DL 9.4 ± 0.4 <DL Fish, Bq/kg dry weight 1.5 ± 0.1 320.7 ± 14.2 0.71 ± 0.07 1.82 ± 0.43 2.4 ± 0.2 219.3 ± 11.6 0.68 ± 0.07 1.3 ± 0.2 341.6 ± 7.8 0.57 ± 0.12 0.49 ± 0.06 1.6 ± 0.1 174.2 ± 17.6 0.39 ± 0.09 x Total dissolved salts (g/l) # number of fish samples The concentration ratio (CR) is a transfer parameter calculated as the ratio between steady-state concentrations in connected compartments of a modul under equilibrium conditions. The following formula was used to calculate the 210Pb CR: CR = Xl / Xe , where: Xl = 210Pb concentration in fish muscle (Bq/kg wet weight), and Xe = 210Pb concentration in sediment (Bq/kg dry weight) [Clulow et al., 1998]. Concentration ratios of 210Pb were 0.086 and 0.019 in Bardawill and Qarun lake respectively. Average (range) specific activity of 210Pb (Bq/kg wet weight) in fish from different areas in the world is given in Table (3). Table 3: Average (range) specific activity of 210Pb (Bq/kg wet weight) and its annual consumption (Bq/y) via fish muscle from different areas in the world. Country Fish type 210 Pb Ref Bq/y Bq/kg wet weight Bardawill 1.82 (0.32 - 5.78)* 2.89 (0.53Egypt** This study Lake 0.55 (0.1 – 1.73) 9.09) 0.49 (0.32 - 0.7)* 0.79 (0.53Qarun Lake 0.15 (0.1 – 0.21) 1.11) 0.09 Syria Sea 0.05 - 0.38 Al-Masry 2000 River 0.05 - 0.10 UK 0.2 Maul, O’Hara 1989 Brazil 1.3 - 1.8 Cunha et al. 2001 8.04-15.34 Japan Sea 0.04 - 0.54 Yamaoto et al. 1994 India River 0.24 (0.21 - 0.32) Hameed et al. 1997 America Sea 0.1 - 7.0 Noshkin, Robtson and wong, 1994 Hong Kong Sea 0.047 Yu et al., 1997 France River 0.9 - 3.0 Lambrechts et al., 1992 Portugal 0.3 (0.08 – 0.69) Fernando P. Carvalho, 1995 84.0 Marshal Island Noshkin et al. 1994 * Bq/kg dry weight, ** Annual consumption rate = 7.5 kg fish = 5.25 kg fish’s muscle. Annual individual effective dose due to fish consumption was calculated using dose per unit activity conversion factors recommended by ICRP (1991), 1 µSv/Bq [Carvalho, 1995]. The average (range) annual effective dose due to 210Pb intake via fish muscle consumption was calculated and found to be 2.89 (0.53-9.09) and 0.79 (0.53-1.11) µSv/y for Bardawill and Qrun lake, respectively. The annual individual effective dose will be higher for those whom have a higher fish consumption rate in the coastal region and around the lakes. Conclusions: Specific activity of 210Pb was measured, in selected fish muscle samples from Bardawill and Qarun lakes, via determination of 210Po (210Pb daughter) using alpha spectrometry after chemical separation. The average 210Pb specific activity (Bq/kg wet weight) in fish (different species) muscle from Bardawill and Qarun lakes was 0.55 and 0.15, respectively. The differences in the average 210Pb specific activity in fish samples of the two lake could be due to differences in the metabolism, feeding patterns and the chemical consumption of the water. The average water salinity of Baradwill and Qarun lakes are 60.5 and 32.4 g/l, respectively. The average annual effective dose due to 210Pb intake via fish muscle consumption was 2.89 and 0.79 µSv/y for Bardawill and Qarun lakes, respectively. These values are higher than that for Syria and lower than that for Japan and Marshal Island, which depend on the specific activity and consumption rate. REFERENCES: Al-Masri, M.S., Mamish, S., Budeir, Y. and Nashwati, A., 2000. 210Po and fish consumed in Syria. Journal of Environmental Radioactivity 49, 345-352. 210 Pb concentrations in Carvalho P. Fernando, 1995. 210Po and 210Pb intake by the Portuguese population: the contribution of seafood in the dietary intake of 210Po and 210Pb. Health Physics 69 (4), 469-480. Clulow F.V., Dave N.K., Lim T.P. and Avadhanula R., 1998. Radionuclides (lead-210, polonium210, thorium-230 and –232) and thorium and uranium in water, sediments and fish from lake near the city of Elliot lake, Ontario, Canada. Environmental Pollution 99 , 199-213. Cunha, I.L., Bueno,L., Fauaro, D.I.T., Maihara, V.A. and Cozzollian, S., 2001. Analysis of 210Pb and Po in Barazillian foods and diets. Journal of Radioanalytical and Nuclear Chemistry 247 (2), 447456. 210 Currie, L.A. 1968. Limits for detection and quantitative determination. Analytical chemistry. 40(3), 586–593. Hameed Shahul, P., Shaheed, K., Somasundaram, S.S.N. and Iyengar, M.A.R., 1997. Bioaccumulation of 210Pb in Kaveri River ecosystem, India. Journal of Environmental Radioactivity 37 (1), 17-27. Hamilton Terry F. and Smith J. David, 1986. Improved alpha energy resolution for the determination of polonium isotopes by alpha-spectrometry. Applied Radiation and Isotopes, 37(7), 628-630. Khater E. Ashraf, 1997. Radiological study on the environmental behavior of some radionuclides in aquatic ecosystem, Ph.D. thesis, Cairo university, Egypt. Khater E. Ashraf, 2000. 210Pb in marine sediment, 5th international conference on High Levels of Natural Radiation and Radon Areas: Radiation Dose and Health Effects, Munich, September 4-7, 2000, Germany. Lambrechts, A., Foulquier, L. and Gariner-Laplace, J., 1992. Natural radioactivity in the aquatic component of the main French rivers. Radiation Protection and Dosimetry 45, 253-256. Noshkin, V.E. Robison, W.L. and Wong, K.M., 1994. Concentrations of 210Po and 210Pb in the diet at the marshall Island. Science of the total environment 155, 87-104. Pietizak-Fils, Z., Chrzanowski, E. and Dembinska, S., 1997. Intake of 226Ra , 210Pb and 210Po with food in Poland. The science of the Total environment 203, 157-165. UNSCEAR, Source, Effects and Risks of Ionizing Radiation. United Nations Scientific Committee on the Effect of Atomic Radiation, 1988. Report on general assembly with annexes, United Nations, New York. Yamamoto, M., Abe, T., Kuwabara, J., Komura, K. and Takiza, Y., 1994. Polonium-210 and Lead201 in marine organisms: intake levels for Japanses. Journal of Radioanalytical Nuclear Chemistry 178, 81-90. Yu, K.N., Moo, S.Y., Young, E.C.M. and Stokes, M.J., 1997. A study of radioactivity in six types of fish consumed in Hong Kong. Applied Radiation and Isotopes 48, 515-519. Journal of Radioanalytical and Nuclear Chemistry, Vol. 270, No.3 (2006) 609–619 Determination of 210Pb in environmental samples Y. Y. Ebaid,1 A. E. M. Khater,2,3* 1 Physics Department, Faculty of Science, Fayum, Cairo University, Cairo, Egypt Center for Nuclear Safety and Radiation Control, Atomic Energy Authority, Egypt 3 Physics Department, College of Sciences, King Saud University, Riyadh, Kingdom of Saudi Arabia 2 National (Received March 14, 2006) Measurement of 210Pb has gained a highly scientific attention due to its wide range of environmental applications. The most commonly used analytical techniques: gamma-spectrometry, beta-counting and alpha-spectrometry were used to measure environmental samples (geological, soil, sediment). Our paper is aiming at comparing the capabilities and limits of application of these three different analytical techniques for 210Pb measurement in various environmental samples. In addition, analytical data of 210Pb measurements with the three different techniques (gammaspectrometry, beta-counting and alpha-spectrometry) are discussed to highlight the degree of comparability and the most probable sources of discrepancies and errors. Based on the demanded investigation, one analytical technique will be chosen for routine analysis, while the other techniques, if they are available, could be used for analytical quality assurance measures. It was essential to compare the analytical efficacy of each technique, which differ concerning the detection limit (MDA), sensitivity, analytical effort, the duration of analysis and waiting time before analysis. Introduction Lead-210 is a very useful radioactive element for environmental studies. Measurements of 210Pb have found extensive applications in the 210Pb geochronometry (measuring the sedimentation rates) of rapidly accumulating sediments in lakes, estuaries and the coastal marine environments.1–10 Measurement of 210Pb in air and in surface soils will afford quantitative information about the flux of radon gas (222Rn) and its daughters in the atmosphere.11–16 It can help in uranium exploration and monitoring the transfer of radionuclides of uranium series in soils and aquatic systems. In the context of luminescence dating, the 210Pb/226Ra activity ratio can give the proportion of 222Rn that can escape from a given sediment, such data being important in the calculation of annual radiation dose rate. Also, 210Pb and its grand-daughter radionuclide (210Po) are included in the group of most highly toxic radioisotopes and provide the major internal natural radiation dose to man. It is approximately 18% of the average dose to the population from internal irradiation due to ingested radionuclides. For some members of the public the dose due to ingestion of 210Pb and 210Po may be far higher due to high intakes of specific foodstuffs such as shellfish.17–19 Lead-210 (T1/2 = 22.2 y) occurs naturally as one of the decay products of the 238U series. Disequilibrium between 210Pb and its parent nuclide, 226Ra (T1/2 = 1600 y), arises through the diffusion of the intermediate gaseous isotope, 222Rn (T1/2 = 3.8 d). A fraction of 222Rn atoms diffuse into the atmosphere and its decay products (mainly 210Pb and its daughter 210Po) are removed from the atmosphere by wet and dry deposition.18 Lead-210 decays by combined emission of weak beta- and gamma-rays and internal conversion electrons to the ground state of 210Bi (T1/2 = 5 d), which in turn decays by emission of beta-particles to a pure alphaemitter 210Po (Fig. 1). Because of the significant selfabsorption of the weak beta-particles of 210Pb and 210Bi (Eβmax = 16 and 63 keV, respectively) and the alphaparticles of 210Po (5.3 MeV), 210Pb measurements frequently need lead and polonium radiochemical separation prior to their individual analyses.20 A number of analytical techniques are available for the measurement of 210Pb, based on different physical and chemical principles. They differ concerning the reachable detection limit, selectivity, analytical effort, reproducibility and stability against differing chemical composition and levels of other natural radionuclides. There are three commonly used radiometric methods for 210Pb measurement in the environmental samples, which are gamma-ray spectrometry of 210Pb, which allows direct measurement in various media, including water, rocks, soil and sediment; beta counter and spectrometry, observing the growth of its daughter 210Bi; and alphaparticle spectrometry of its grand-daughter 210Po, assuming radioactive equilibrium between the two radionuclides.18,19,22 A systematic view of methodical principles and details of the 210Pb measurement methods is a prerequisite to compare the analytical power of the different techniques, to guarantee the comparability of the results from these different methods and to know the probable sources of data discrepancies and errors.19 * Present address; Physics Department, College of Sciences, King Saud University, P.O. Box 2455, Riyadh 11451 Kingdom of Saudi Arabia. E-mail: [email protected] 0236–5731/USD 20.00 © 2006 Akadémiai Kiadó, Budapest Akadémiai Kiadó, Budapest Springer, Dordrecht Y. Y. EBAID, A. E. M. KHATER: DETERMINATION OF 210Pb IN ENVIRONMENTAL SAMPLES This work is aimed at comparing the capabilities of different techniques (gamma-spectrometry, beta210Pb counting and alpha-spectrometry) for determination and their limits of application for the purposes of environmental samples analyses. Experimental Sample preparation The first step of analysis involves the drying of the sample matrix at an oven temperature lower than 100 °C, crushing, grinding and sieving through 2 mm sieve mesh size. For ashing, 10 grams of the dried sample was moistured with nitric acid (HNO3) till no further reaction occurs. The sample was dried on a sand bath then ashed at 550 °C for 6–8 hours. If the sample residue was not free of organic carbon, which can be recognized by a dark brown or black colored ash, the ashing process had been repeated again. Finally the sample ash was ground and homogenized. Analytical techniques for the determination of 210Pb in environmental samples Gamma-spectrometry: The dried samples were transferred to polyethylene containers of 100 cm3 capacity. Lead-210 specific activities were measured using well calibrated gamma-spectrometry based on hyper pure germanium (HpGe) detectors. The HpGe detector had a relative efficiency of 40% and full width at half maximum (FWHM) of 1.95 keV for 60Co gamma-energy line at 1332 keV. The gamma transmissions used for activity calculations was 46.5 keV with a branching ratio of 4.05%. The gammaspectrometers were calibrated using 210Pb standard solution in the same sample–detector geometry.23 The lower limit of detection, with 95% confidence, is 0.44 Bq for 1000 minute measuring time.24 Beta-counting: One milliliter of Pb2+ carrier (20 mg/ml) is added to 3–5 g of the ashed sample and then dissolved using mineral acids (HNO3, HF and HCl). Lead is leached with hydrobromic acid (HBr) as tetrabromo-complex, extracted with trioctylamin/toluene and back-extracted with HCl. After addition of Bi3+ carrier, Bi3+ traces are separated by precipitation as BiOCl. Finally lead is precipitated as PbCrO4 and collected on a filter paper. The chemical recovery of 210Pb on the filter was determined gravimetrically. After waiting for 8–10 days, the filter is covered with a filter paper of equal size to hold back the low energy betaparticles of 210Pb and the alpha-particles of ingrown 210Po. The high energy beta-particles of 210Bi (1.2 MeV) are counted using a calibrated low background gas proportional counter. The counter was calibrated using 210Pb standard solution sources prepared in the same condition as the analyzed samples. The counting efficiency is about 40% and the lower limit of the procedure, with 95% confidence, is 7 mBq/sample for 1000 minute counting time.24 The details of the analytical steps are given in Fig. 2. Alpha-spectrometry: The dried sample (1–2 g) is spiked, for chemical recovery and activity calculation, with about 80 mBq 208Po and dissolved using mineral acids (HNO3, HF and HCl). Finally the sample residuals is dissolved in about 30 ml 0.5M HCl. The sample is heated to 85 °C and about 100 mg of ascorbic acid is added to the hot solution to reduce the iron Fe(III) to Fe(II). Then, polonium isotopes are auto-deposited from the solution at temperatures between 80–90 °C onto rotating, clean mirror finishing, stainless steel disk fixed in a Teflon disk holder.25,26 The plated disk is measured using an alpha-spectrometer (Canberra 4701 vacuum chamber) based on passivated implanted planar silicon (PIPS) detector with 450 mm2 surface area, about 25% counting efficiency and 20 keV resolution for 241Am alpha-energy at 5.48 MeV, and connected to a computerized multichannel analyzer (MCA) operating with Genie 2000 software (Canberra). The average chemical recovery is 75%, and the individual values ranged from 50 to 100%. The sample is measured for 1000 minutes, applying a lower limit of detection of 1 mBq, with 95% confidence.24 The details of the analytical steps are given in Fig. 3. Fig. 1. Decay chart of 210Pb 610 Y. Y. EBAID, A. E. M. KHATER: DETERMINATION OF 210Pb IN ENVIRONMENTAL SAMPLES Fig. 2. Flowchart of the radiochemical analysis of 210Bi (210Pb) by beta-counting 611 Y. Y. EBAID, A. E. M. KHATER: DETERMINATION OF 210Pb IN ENVIRONMENTAL SAMPLES Fig. 3. Flowchart of the radiochemical analysis of 210Po (210Pb) by alpha-spectrometry Table 1. Comparison of parameters of various analytical techniques for the determination of 210Pb in environmental samples Method Sample size, g Counting time, minutes Sensitivity, s–1.Bq–1 Background, cpm Counting efficiency, % MDA,* mBq, in 1000 minutes Duration of complete analysis Gamma-ray spectrometry 100 1000 2.9.10–4 0.5 7 440 1 day Beta-counting 5 1000 2.5 0.5 40 7.1 >10 days Alpha-spectrometry 1–3 1000 5 0.005 20 1 3–6 moths** * MDA: Minimum detectable activity. ** 3 days, in the case of Pb–Po secular equilibrium existence. Results and discussion Comparison of the main parameters of the three different analytical techniques, gamma-spectrometry, beta-counting and alpha-spectrometry is given in Table 1. They differ over a wide range of analyzed sample size and counting system background and minimum detectable activity (MDA). It is noticeable that alpha-spectrometry achieves the lowest MDA (1 mBq/sample), amongst the three analytical techniques, while the MDA for gamma-spectrometry is the highest amongst all three techniques. Concerning the duration of the 210Pb complete analysis (source preparation and measurement), it is ranged from one day for gamma-spectrometry to more than 10 days for betacounting. While for alpha-spectrometry, the complete analysis duration is at least three days for sample dissolution, alpha-source preparation and alphaspectrometry, and varied widely according to the time of sample dissolution that depends on sample type. Also, the time needed before starting sample analysis differs and depends on the used analytical techniques. Analysis of 210Pb using both gamma-spectrometry and betacounting is possible without time delay before starting 612 the analysis. For alpha-spectrometry, the time delay before analysis depends on 210Pb–210Po secular equilibrium condition in the sample. If the secular equilibrium is already existed, the samples could be analyzed without time delay. Otherwise, it is essential to first get rid of 210Po existed in the samples via either auto plating of 210Po on a stainless steel disk or sample ashing at 600 °C.27 Accordingly, 210Po can be analyzed after 3–6 months delay. It should be mentioned that the ingrowth factor of 210Po as a decay product of 210Pb during the storage time should be taken into consideration. Ideally, to be sure of reaching secular equilibrium, the sample should be stored at least for two years, especially for samples with expected higher 210Po concentration than that of 210Pb. Three aspects should be considered for evaluating the methods. (1) The attainable detection limit decides whether a method is successfully applicable at all for the investigations. (2) The duration of a complete analysis can exclude methods of longer duration if there is an urgent need for the results. (3) The total expenditure in work and equipment has to be considered if economic limitations are important.22 Based on these aspects one method is chosen for 210Pb routine measurements for the Y. Y. EBAID, A. E. M. KHATER: DETERMINATION OF 210Pb IN ENVIRONMENTAL SAMPLES demanded investigation but as necessary measures of analytical quality assurance some selected samples should be measured using another analytical technique. To guarantee the comparability of the results from these different analytical methods, the advantages and disadvantages of each method and the sources of data discrepancies and errors should be cleared. In this work, it is planned to apply these aspects using 210Pb measurement results of some selected geological, processed geological, soil and sediment samples. Gamma-ray spectrometric analytical technique: Its main advantages are being fast, nondestructive, relatively simple sample preparation with no need of preliminary chemical separation, and direct analysis without delaying time through the measurement of 46.5 keV gamma-energy transition. However, the main disadvantages are its relatively high MDA and the often difficult corrections for self-attenuation in the sample matrix.28–30 The relative high MDA of gammaspectrometry is due to both the low emission probability (4.05%) and low energy transition of gamma-line. For a given sample container volume and geometry, the selfattenuation can significantly vary from sample to sample because it depends strongly on both the composition and apparent density of the sample.29 Self-attenuation can be theoretically calculated using physical models of interaction between gamma-rays and matter, computed with a Monte Carlo technique. Alternatively, some experimental approaches have been proposed and mentioned by PILLEYRE et al.19 One approach dealt with the determination of absolute activity of large volume geological samples, without being hindered by selfattenuation. It was based on replicate counting of increasing volumes of the unknown samples. Good results were obtained but it was time consuming. Another approach have reported a method based on an evaluation of the transmission of low-energy gammarays from a 210Pb point source placed on an aluminum container in the presence and absence of the sample. In addition, others attempted to establish a direct correspondence between the measured count rate for the sample and the count rate expected for material identical to that used for efficiency calibration using gamma-ray transmission, this was for measuring 241Am (at 59.6 keV), where the situation is nearly the same as for 210Pb.19 Beta-particle counting of 210Bi technique: The main advantage is the relatively low limit of detection, in the range of several mBq per sample. The main disadvantages are being destructive, the need of radiochemical separation and beta-particle source preparation, the need of waiting 10–30 days in order to count the prepared source and indirect measurement of 210Pb in the analyzed samples. There are different analytical methods for lead separation such as ionexchange method with EIChrome Sr. Spec. resin or Dowex 1x8 resin, and solvent extraction methods with diethyl dithiocarbanic acid (DDTC) or trioctylamin/toluene. The lead reagent, which is used as a yield tracer (carrier), could be a source of error. CLAYTON17 had analyzed a sample of lead of Tudor origin (virgin) and modern commercial reagent grade lead nitrate and the specific activity of 210Pb–210Po were 10.9±0.7 and 500±40 Bq/kg lead respectively.19 The specific activity of 210Pb–210Po in the lead nitrate, which used in our analysis, is 18.2±2.3 Bq/kg (29.1±3.7 Bq/kg lead), as shown in Table 5. Alpha-spectrometry of 210Po technique: The main advantages are the excellent low limit of detection (in the range of few mBq per sample), the selectivity of polonium plating onto the stainless steel disk and the relatively less chemical preparation steps compared to that is associated with beta-counting. Waiting time required to achieve the analysis, being destructive and the need for careful chemical treatment are considered as the main disadvantages of this technique.31,32 Specific activity of 210Pb (Bq/kg) in geological, processed (geological samples have been exposed to some physical and chemical processing) and soil, and sediment samples, and their average are given in Tables 2, 3 and 4 respectively and shown in Fig. 4. The relationships and data correlations of 210Pb specific activity that were measured using three different analytical techniques (gamma-spectrometry, betacounting and alpha-spectrometry) in all samples and in each sample type (i.e., geological, processed, soil and sediment) are shown in Figs 5 and 6, respectively. For geological samples, the existence of some discrepancies (but not vivid) in the results of some samples (specially the geological and processed samples) obtained from the different techniques was noticed. On the contrary, soil samples results showed acceptable concurrence amongst the different techniques. For sediment samples, the 210Pb specific activity measured using gamma-spectrometry and alphaspectrometry has trend of comparability of the results, although some samples has a higher concentration of 210Pb using one technique more than the other, without the existence of clear trends, as shown in Fig. 4. Generally, the average specific activity of 210Pb in each sample type for each analytical technique and its over all average (for all samples of the same type and all analytical techniques) are mostly comparable and within the error values, as shown in Fig. 4. It is obvious that the specific activity of 210Pb measured using alphaspectrometry of 210Po is slightly higher than that was measured by gamma-spectrometry and could be explained by the sample self-attenuation. The sample self-attenuation correction has not been applied for our gamma-measurements. The results obtained for all samples by the different techniques (Fig. 5), are strongly correlated with correlation coefficients (R2) very close to 613 Y. Y. EBAID, A. E. M. KHATER: DETERMINATION OF 210Pb IN ENVIRONMENTAL SAMPLES Accordingly, careful efficiency calibration should be carried out to elude this problem. On the other hand, another issue concerning self attenuation problem should be considered, where empirical and experimental methods could be used to take the self attenuation in the lower energies region into consideration.21,29 unity. The difference between the data linear fitting and the dashed line, represents the assumed identical results, is clear especially for highly active samples (geological and processed samples) where the alpha-spectrometry results seemed higher than that obtained by gammaspectrometry. These differences could be explained by the expected self attenuation in some samples. Table 2. Specific activity of 210Pb (in Bq/kg) in geological, processed and soil samples using various analytical techniques Method Sample G 1+ G2 G3 P 1++ P2 P3 P4 S 1+++ S2 S3 S4 S5 Gamma-spectrometry A* ± E** 279.0 ± 5.6 34.8 ± 3.8 64.9 ± 5.3 251.0 ± 14.8 154.0 ± 6.9 202.0 ± 14.1 173.0 ± 17.3 19.8 ± 5.8 20.7 ± 5.2 15.1 ± 0.8 25.4 ± 4.8 31.6 ± 5.1 Beta-counting A ± E 251.3 ± 2.7 43.0 ± 0.9 65.2 ± 1.0 216.1 ± 1.9 277.4 ± 3.3 290.1 ± 2.8 116.7 ± 1.3 14.0 ± 0.7 17.4 ± 0.6 15.1 ± 0.8 18.3 ± 0.8 17.2 ± 0.7 Alpha-spectrometry A ± E 396.3 ± 12.6 36.5 ± 2.4 85.3 ± 4.3 355.9 ± 10.7 236.9 ± 11.4 300.6 ± 8.6 234.2 ± 7.2 19.1 ± 1.1 23.6 ± 1.3 19.2 ± 1.0 21.1 ± 0.9 21.3 ± 1.1 * Specific activity, Bq/kg. ** Error (statistical and counting error only). + Geological sample. ++ Processed sample (physical treated geological samples). +++ Soil sample. Table 3. Specific activity of 210Pb (in Bq/kg) in sediment samples using gamma-ray and alpha-spectrometry techniques Sample No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 210Pb* 29.34 13.95 80.99 9.88 19.5 24.5 11.08 13.54 21.1 14.07 7.9 25.61 7.08 22.05 23.71 81.75 14.63 29.63 8.72 24.8 16.93 14.82 22.1 29.63 9.44 19.76 11.4 23.71 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± E* 3.4 1.37 3.13 1.02 1.94 5.6 0.98 1.42 7.0 1.22 0.79 2.59 0.9 3.58 3 5.1 1.5 2 1.1 6.7 1.8 1.8 5.1 3.3 0.8 2.2 1.4 2.6 * Statistical and counting error only. 614 210Pb** 73.35 18.78 96.01 15.71 16.09 28.8 17.97 14.49 25.2 14.83 8.07 31.61 12.38 17.54 17 81.41 14.51 32.68 12.29 33 22.04 23.26 24.7 34.75 13.86 25.42 23.31 13.39 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± E 3.4 1.2 5.7 0.8 1.3 2.1 1.3 1.2 2.5 1.2 0.7 4.7 1.3 1.3 1.6 4.3 0.9 1.7 1.4 3.2 1.9 1.1 2.4 2.6 1.1 2.9 2.4 1.5 Y. Y. EBAID, A. E. M. KHATER: DETERMINATION OF 210Pb IN ENVIRONMENTAL SAMPLES Table 4. Average specific activity of 210Pb (in Bq/kg) in environmental samples using various analytical techniques Sample type Geological Processed geological Soil Sediment Gamma-spectrometry 126.2 ± 76.9, 133.2* (34.8–279.0) [3]+ 195.0 ± 21.1, 42.3 (154.0–251.0) [4] 22.5 ± 2.8, 6.3 (15.1–31.6) [5] 22.7 ± 3.4, 18.0 (7.1–81.8) [28] Beta-counting 119.8 ± 66.0, 114.4 (43.0–251.3) [3] 225.1 ± 39.6, 79.2 (116.7–290.1) [4] 16.4 ± 0.8, 1.8 (14.0–18.3)[5] – – Alpha-spectrometry 172.0 ± 112.7, 195.2 (36.5–396.3) [3] 281.9 ± 29.1, 58.1 (234.2–355.9) [4] 20.9 ± 0.8, 1.8 (19.1–23.6) [5] 27.2 ± 4.0, 21.3 (8.1–96.0) [28] Average 139.6 ± 16.7, 28.9 (119.8–172.7) [3] 234.2 ± 25.4, 44.1 (195.0–281.9) [4] 19.9 ± 1.8, 3.2 (16.4–22.5) [5] 24.9 ± 2.3, 3.2 (22.7–27.2) [28] * Average ± standard error, standard deviation. + (range) [number of samples]. Fig. 4. Specific activity of 210Pb in environmental samples (geological, processed geological, soil and sediment) using gamma-spectrometry, beta-counting and alpha-spectrometry 615 Y. Y. EBAID, A. E. M. KHATER: DETERMINATION OF 210Pb IN ENVIRONMENTAL SAMPLES Fig. 5. Correlations between the specific activity of 210Pb in environmental samples measured by various analytical techniques Table 5. Comparison of the specific activity of 210Pb (in Bq/kg) in some selected reference material samples using gamma- and alpha-spectrometry and their reference values Sample (1)& IAEA-384, sediment IAEA-326, soil (4) IAEA-327, soil (2) IAEA-135, marine sediment (2) IAEA-RGU, uranium ore (2) Lead nitrate, Pb(NO3)2++, Analytical grade (2) * Specific activity, Bq/kg. ** Error (statistical and counting error only). + Information value. ++ Used as carrier. & Number of analysis. 616 Gamma-spectrometry A* ± E** 23.5 ± 1.3 43.4 ± 6.7 – 50.61 ± 7.58 – – Alpha-spectrometry A±E – 43.14 ± 2.02 51.8 ± 4.8 – 5092 ± 283 18.17 ± 2.32 Reference value 23.5 (22.2–24.2) 52.5 (47.9–57.1) 58.8 (53.9–63.7) 48 (42.2–54.1)+ 4914 (4844–4984) – Y. Y. EBAID, A. E. M. KHATER: DETERMINATION OF 210Pb IN ENVIRONMENTAL SAMPLES Fig. 6. Correlations between the specific activity of 210Pb in various environmental samples measured by various analytical techniques The specific activity of 210Pb in each sample type using three analytical techniques is shown in Fig. 6. The correlation coefficient between gamma- and alphaspectrometry measurements are stronger than that between gamma-spectrometry and beta-counting measurements. These discrepancies are very clear for soil samples without any clear reason. It is well known that gamma-spectrometry measurements are performed using bulk amounts of samples, so, the homogeneity issue does not bother the analysts. On the other hand, regardless of their good MDA, both alpha- and betaspectrometry techniques are performed based on a relatively smaller sample size. So, this might brings up the homogeneity problem. Regarding the geological and processed geological samples, the discrepancies in the results among the three techniques could be explained by the lack of sample homogeneity and the existence of hot spots. This could be more clear in the case of the processed samples since they are both physically and chemically (washed) treated. Twenty eight sediment samples were analyzed using two different techniques (gamma- and alphaspectrometry) are given in Table 3 and shown in Fig. 4. 617 Y. Y. EBAID, A. E. M. KHATER: DETERMINATION OF 210Pb IN ENVIRONMENTAL SAMPLES Fig. 7. Specific activity of 210Pb in some selected reference samples with their reference values using various analytical techniques The correlation coefficient was calculated for these the two sets of results and was 0.9. Some samples showed good agreement for both techniques (samples 8, 10 11, 16, 17 and 18), (Figs 5 and 6). However, other samples showed distinct discrepancies. The homogeneity problem may be a major factor, in addition to the necessity of sample self attenuation correction that was not corrected in all of our results. The specific activity of 210Pb in some selected reference materials using gamma- and alphaspectrometry techniques are given in Table 5 and shown in Fig. 7. The results are showing good accuracy for both techniques compared to the given reference values. One reference sample was analyzed using both techniques and they gave a spectacular agreement, though relatively lower than the reference value but it falls within the reference range. It should be mentioned that the IAEA reference samples often follow a tedious procedure of mixing and strict homogeneity tests prior to releasing to laboratories for use as reference materials. So, these results are considered supportive of our point of view regarding the homogeneity issue. Conclusions For 210Pb analysis in environmental samples, the three analytical techniques give comparable results for the same sample set. For routine analysis, the used analytical technique should be chosen carefully based on advantage and disadvantage of the each technique, and the analysis requirements. Gamma-spectrometry is easier, needs less man-power and cost than the other techniques. Best is the direct measurement of 210Pb in a 618 relatively large volume sample with no waiting time before analysis and minor effect of sample inhomogeneity problem. Its major advantages are its relatively high minimum detectable activity (MDA), about 0.44 Bq/sample, and the necessity to correct the counting efficiency for the gamma-ray attenuation due to sample matrix and composition. Beta-counting needs tedious chemical work and waiting time (2–3 weeks) before measurement for 210Bi build up in the sample source, but no waiting time needed before sample analysis. Its MDA (0.007 Bq/sample) is much lower than that of gammatechnique. So it is considered moderate regarding the time consumption. Alpha-spectrometry needs relatively simple chemical sample treatment and source preparation and no waiting time before measurement. It needs also to ensure a certain degree of equilibrium between 210Pb and its grand-daughter 210Po, which requires waiting for 3–6 months after the first 210Po analysis or two years especially for the sample with an expected enrichment of 210Po to 210Pb. Its MDA (0.001 Bq/sample) is the lowest amongst the three techniques. On the other hand, using a relatively small size of the sample for beta-counting and alpha-spectrometry analytical techniques could increase the analytical error due to the possible lack of sample homogeneity. 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