Polonium-210 budget in cigarettes

Transcription

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
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
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
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
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
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.
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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.
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
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).
2.1. 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
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
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,
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
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
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
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
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
238
Phosphate samples
(Bq/kg dry weight)
P1
Ore rock
P2
Wet rock
P3
Wet screening
P4
P5
Slime
P6
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
Main farm.
c
New farm.
b
235
UE
UE
262
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
226
210
234
226
P1
Ore rock
P2
Wet rock
P3
Wet screening
P4
P5
Slime
P6
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
Pb/226Ra
U/238U
Ra/228Ra
0.63
0.79
1.08
1.11
1.27
0.98
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
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
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
the support received from the Central Safety Department Forschungszentrum
Karlsruhe gmbH and the International Bureau Julich in Germany.
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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).
Totally dissolved with HNO3, HF, HCl and
H3BO3
Anion-Exchange
Dowex 1x2, 50 -100 mesh
wash with 9 M HCl
eluate with NH4I/1M HCl
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
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,
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.
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).
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
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
–
–
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
Very well sorted
–
Moderately sorted
Moderately sorted
Very well sorted
Poorly sorted
Moderately sorted
–
Moderately sorted
–
Moderately sorted
Moderately sorted
Moderately sorted
Moderately sorted
Moderately sorted
Poorly 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)
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 sorted
Poorly 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
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
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,
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
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
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
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.
162
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.
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
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
165
166
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.
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.
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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.
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Mélières, Michel Pourchet and Sandrine Richard, Journal of
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Marine and Environmental Sciences, second ed . Clarendon press, Oxford.
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41, 323-329.
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R., Danesi P., Gy Kis-Benedek, J. Environmental
Radioactivity, 1997, 37(3), 355-372.
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Safety. http://www.gr.is/nsfs/klemola.htm.
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and Isotopes, 2002, 56, 387-392.
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Sansone, Applied Radiation and Isotopes, 2000, 53, 115-120.
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
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
Heat to boiling,
Add 200 mg Ascorbic acid
Po deposition on a rotating
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)
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
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
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,
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.
This study reports the occupational radiation doses received by the workers in
Abu-Tartor phosphate mine. Occupational exposures arise from conventional
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
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
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.
3.1. 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
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
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
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-
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
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.
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.
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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
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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,
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].
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
17
17
17
18
2-2-3-3 Plants
18
3
2-2-3-4 Milk
19
19
2-2-4 Determination
21
22
22
2-2-5-2 Calculation of uranium isotopes
specific activities in the sample
23
23
25
25
2-2-7 References
26
2-3 Determination of Lead-210
27
2-3-1 Introduction
27
27
27
27
28
2-3-3-3 Plants
28
2-3-3-4 Milk
28
29
2-3-4 Determination
31
32
32
32
33
33
2-3-7 References
34
2-4 Determination of Polonium-210
2-4-1 Introduction
35
35
4
35
35
35
36
2-4-3-3 Plants
36
2-4-3-4 Milk
36
36
2-4-4 Determination
37
38
38
38
38
39
2-4-7 References
40
3-Man-Made radionuclides;
3-1 Determination of Plutonium isotopes
41
41
3-1-1 Introduction
41
41
42
42
43
3-1-3-3 Plants
43
3-1-3-4 Milk
43
43
3-1-4 Determination
46
47
47
48
48
5
50
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.
9
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.
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
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
magnetic bar.
Note A).
10
Schematic Representation of the Radiochemical Procedure of Uranium
Ashed Samples Material
add yield tracer U-232
Digestion with HNO3,HCl and HF
Extraction with TOPO/Cyclohexane
Aqueous Phase :
discard
Organic Phase:
Backextraction with NH4F/HCL
Organic Phase:
discard
Aqueous Phase:
add TiCl3, La(NO3)3, HF
wash precipitation with 1.5 M HF
dissolve in H3BO3 (saturated)/HNO3 (65%)
add H2O2 (30%)
dissolve in 9 M HCl
Anion-Exchange
Cl- form
wash with 9 M HCl
elute with 1M HNO3
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
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
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
in Bq/g or Bq/l
in Bq/g or Bq/l
net count rate in the U-238-Peak
net count rate in the U-232-peak
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.
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.
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.
18
sample ash.
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
2-2-3-2 Biological Sample Materials (plants, milk, meat and fish)
2-2-3-2-1 Plants:
homogenize the dried sample.
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.
HNO3 in a 250 ml glass beaker and cover it with a watch glass.
19
2-2-3-2-2 Milk:
10. Cover the samples with HNO3 (65%) and add 229Th tracer (50-100 mBq) for chemical
magnetic bar.
Note A).
10. Cover the samples with HNO3 (65%) and add 229Th tracer (50-100 mBq) for chemical
magnetic bar.
Note A).
20
Schematic Representation of the Radiochemical Procedure of Thorium
add yield tracer Th-229
Digestion with HNO3,HCl and HF
Aqueous Phase :
discard
Organic Phase:
Backextraction with HN4F/HCL
Organic Phase:
discard
Aqueous Phase:
add TiCl3, La(NO3)3, HF
Anion-Exchange
NO3- form
wash with 8 M HNO3
elute with 9M HCl
dissolve with 4 M H2SO4
add electrolytic solution, pH=1.7
Electrodeposition
Alpha-Spectrometry
21
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.
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.
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.
8. Transfer the solution into a 100 ml polyethelene centrifuge tube.
10. Repeat the addition of two times 2 ml La(NO3)3 (25 mg La3+/ml) each, centrifuge the
decanting.
for 5 min at 3000 rpm. Discard the aqueous phase after decanting.
Cool the sample solution to room temperature.
Column Preparation: Transfer about 1 g Dowex (1 x 2, 50-100 mesh, NO3-form)
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.
1 min.
ethanol.
η=
where:
η
Cn,Th-229
CEx,Th-229
C n ,Th − 229
C Ex ,Th − 229
⋅ 100
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
2-2-5-2 Calculation of thorium isotopes specific activities in the sample;
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
count rate in the Th-232-peak, in s-1
background count rate in the Th-232-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
activity of Th-229, added for yield determination, in Bq
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
in Bq/g or Bq/l
in Bq/g or Bq/l
net count rate in the Th-232-Peak
,
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
k1-β
25
k1-α = 3.000.
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

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
2-2-7 References
•
•
•
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.
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. 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
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.
2-3-3-2-1 Plants:
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.
Note A).
2-3-3-2-2 Milk:
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.
29
Note A).
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.
Note A).
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
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
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
)
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
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.
34
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
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.
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. 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).
6. Add 3 ml HCl for three times and evaporate to near dryness.
36
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.
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.
magnetic bar.
37
6. Add 3 ml HCl for three times and evaporate to near dryness.
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
Heat to boiling,
Add 200 mg Ascorbic acid
Po deposition on a rotating
Rotate the disk for one hour
at 90 oC
Alpha Spectrometry
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
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
k1-β
k1-α = 3,000.
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
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.
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
sample ash.
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.
43
3-1-3-2-1 Plants:
homogenize.
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.
HNO3.
7. Boil the sample solution and add carefully to the hot solution 2.5 g NaNO2. Cool the
3-1-3-2-2 Milk:
2. Cover the samples with HNO3 (65%) and add Pu tracer (50-100 mBq) for chemical
magnetic bar.
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 .
2. Cover the samples with HNO3 (65%) and add Pu tracer (50-100 mBq) for chemical
44
magnetic bar.
Note A).
6. Dissolve the sample residue in 100 ml 8M HNO3.
45
Schematic Representation of the Radiochemical Procedure of Plutonium
add NaNO2, filtrate
add NaNO2, filtrate
Aqueous Phase:
discard
Organic Phase:
Backextraction with
Organic Phase:
discard
Aqueous Phase:
add NaNO2
Anion-Exchange
wash with 9 MHCl
eluate with 0.36 M HCl/0.01 M HF
add (NH4)2C2O4 (4%)
Electrodeposition
Alpha-Spectrometry
46
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.
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.
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.
8. Transfer the solution into a 100 ml polyethelene centrifuge tube.
10. Repeat the addition of 2 ml La(NO3)3 (25 mg La3+/ml) two times, centrifuge the
decanting.
for 5 minutes at 3000 rpm. Discard the aqueous phase after decanting.
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)
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.
1 min.
ethanol.
η=
where:
η
Cn,Pu-236
CEx,Pu-236
C n , Pu − 236
C Ex , Pu − 236
⋅ 100
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
APu-236
tM
ε
3-1-5-2 Calculation of plutonium isotopes specific activities
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
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
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
,
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
k1-β
often show more counts than background measurements of clean stainless steel disk. This
advisable to preselect an error probability of 0.0014 for errors of 1st order. This means that
k1-α = 3.000.
50
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

Quality control measurements are necessary to provide documentation to show
the reliability of the achieved results. The results reliability is a function of precision
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:
•
•
•
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,
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].
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
add NaNO2, filtrate
Extraction with TOPO/
Cyclohexane
Aqueous Phase:
discard
Organic Phase:
Back-extraction with
Organic Phase:
discard
Aqueous Phase:
wash precipitation with 1.5 M HF dissolve
H3BO3 (saturated)/HNO3 (65%) add NaNO2
Anion-Exchange
wash with 9 M HCl
eluate with 0.36 M Hcl/0.01 M HF
add (NH4)2C2O4 (4%)
Electro-deposition
Alpha-Spectrometry
plutonium analysis (LLE).
Totally dissolved with HNO3, HF, HCl and
H3BO3
Anion-Exchange
Dowex 1x2, 50 -100 mesh
wash with 9 M HCl
eluate with NH4I/1M HCl
dissolve with 0.1 M HCl
add (NH4)2C2O4 (4%)
1 Amp current applied for 30 min
Electro-deposition
Alpha-Spectrometry
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
3.29>u>2.58
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
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.
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
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
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
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
Egypt
14.1
Po
Finland
10.8
Germany
19.2
Japan
22.4
Norway
8.6
France
23.2
Philippines
10.7
Russia
14.1
Turkey
14.3
Karali et al., 1996
Various
18.1
Parfenov, 1974
Notes:
*In mBq/g
Assuming 1.2 g tobacco per cigarette
+
230
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
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
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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.
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
Fig. 2. Flowchart of the radiochemical analysis of 210Bi (210Pb) by beta-counting
611
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
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
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
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
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)
–
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
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. 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 is strongly
recommended. On the other hand if the samples are
expected to have a relatively low 210Pb specific activity,
either alpha-spectrometry or beta-counting are
recommended. The choice between the alphaspectrometry and beta-counting could be decided based
on the accuracy needed and the time limits for the
analyst.
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