|Year : 2016 | Volume
| Issue : 2 | Page : 101-106
Natural radioactivity levels of the Egyptian phosphate rocks using BGO detector based portable gamma-ray spectrometer
Hesham Ahmed Yousef1, Gehad Mohamed Saleh2
1 Department of Physics, Faculty of Science, Suez University, Suez, Egypt
2 Department of Geology, Nuclear Materials Authority, P. O. Box 530, El Maadi, Cairo, Egypt
|Date of Web Publication||13-Sep-2016|
Hesham Ahmed Yousef
Department of Physics, Faculty of Science, Suez University, Suez
Source of Support: None, Conflict of Interest: None
Gamma-ray surveys are used in geological, geochemical, and environmental mapping for mineral exploration. Natural radioactivity levels for forty phosphate sample localities on the Eastern Desert, Nile Valley, and Western Desert, Egypt, were measured using a gamma-ray spectrometer with high accuracy. From the obtained results, the average values of the annual effective dose were 0.19, 0.28, 0.29, and 0.15 mSv/year for Safaga, Abu.Tartur, El-Sebaeya, and Hamrawayn, respectively. The measured values of natural radionuclides in the studied samples are higher than the world average activity values. This study could be useful as baseline data for radiation exposure to phosphate and their impact on human health.
Keywords: Dose, exposure, phosphate rocks, radiation measurements, radioactivity
|How to cite this article:|
Yousef HA, Saleh GM. Natural radioactivity levels of the Egyptian phosphate rocks using BGO detector based portable gamma-ray spectrometer. Radiat Prot Environ 2016;39:101-6
|How to cite this URL:|
Yousef HA, Saleh GM. Natural radioactivity levels of the Egyptian phosphate rocks using BGO detector based portable gamma-ray spectrometer. Radiat Prot Environ [serial online] 2016 [cited 2019 Jun 25];39:101-6. Available from: http://www.rpe.org.in/text.asp?2016/39/2/101/190395
| Introduction|| |
Radiometric surveys and maps are applicable in several fields of science. They retain their geological and geophysical information for mineral prospecting, geochemical mapping, structural geology and enable the comparison of geological features over large regions. It has also been successfully applied in emergency situations for mapping the contamination from nuclear fallout and for the location of lost radioactive sources. Components of natural environments such as soils, rocks, sediments, vegetation, air, and water include some naturally occurring radioactive materials (NORMs). These materials may contain 238 U,232 Th series, their radioactive daughters, and the primordial radioactive isotope 40 K. Human activities such as mining and exploitation of natural resources may result in technologically enhanced NORM, which can influence exposure to natural sources of radiation. The radioactive elements can be found in the soil, water, and food items of man and animal. The increase in radioactivity of the soil is small compared to the radioactivity from naturally occurring radioactive nuclides. Phosphate rock is an important raw material used for manufacturing a different type of phosphatic fertilizers. Fertilizers are the main source of radioactivity in cultivated soils. Phosphate rocks contain relatively high amounts of NORMs from 238 U,232 Th, their respective descendants, and 40 K in concentrations that depend on geographical and geological origin. The largest phosphate rock deposits worldwide are located in one belt covering all North African countries and continue through Jordan and North West of Saudi Arabia. The Egyptian phosphate is widely distributed in many localities on the Red Sea, Nile Valley, and Western Desert. The deposits in the first two districts are relatively rich in phosphate and are exploited at several mines, but those of the Western Desert are of low grade except at Abu-Tartur mine. Phosphate rock is the starting raw material for all phosphate products and its decay products tend to be elevated in phosphate deposits of sedimentary origin. Occupational exposures mainly occur during mining processing and transportation of phosphate rock, as well as during transportation and utilization of phosphate fertilizers. The investigated samples locations were measured in Safaga and El-Hamrawayn areas of the Eastern Desert along the Red Sea. The phosphate deposits of the Eastern Desert are along the beach of Red Sea from Safaga to Quseir between latitude (25°00'–26°47') and longitudes (33°45'–34°25'). Also from Abu-Tartur phosphate project is the largest phosphate mines in the Middle East. The mining area is located in the heart of the Western Desert of Egypt (60 km from El-Kharga City and 10 km from the main road between the two oases El-Kharga and El-Dakhlah),, but El-Sebaeya area found in the south of Esna city (Luxor), Western Nile Valley.
The present work aimed to determine the radioelement concentrations of 238 U,226 Ra,232 Th, and 40 K in the phosphate fields. They may be used to estimate and assess the terrestrial radiation dose to the human population and to identify areas of potential natural radiation hazard. This study is an important collection of data on radiological protection, including doses expected to be received by exposed individuals and monitoring considerations with the total annual exposure of phosphate worker and provide useful information in the monitoring of environmental contamination by natural radioactivity.
| Materials and Methods|| |
Forty sample locations were measured in the areas under study. The distance between each two locations is about 300 m. The detector placed down on the sample location and takes 2 min to assay and note the result and shows the data analysis results. The studied phosphate samples were investigated radiometrically using RS-230 BGO Super-Spec portable radiation detector, handheld unit spectrometer survey meter with high accuracy, and its average probable measurement errors was about 5%. A precision can be expected from field assays with a scintillation gamma-ray spectrometer using a sampling time of 2 min. The main factors that reduce assay precision are the statistical nature of radioactivity, variable background radiation due to atmospheric radon, and the variable water content in rocks.
RS-230 has a (6.3 cu inch) BGO detector provides typically 3× equivalent performance over comparably sized sodium iodide detectors used as the detector survey instrument for the geophysical industry. This detector is full assay capability with data in K%, U (ppm), Ra (ppm) and Th (ppm), no radioactive sources required for proper operation. The detector is an independent private company (Radiation Solutions Inc., 386 Watline Ave, Mississauga, Ontario, Canada, L4Z 1 × 2). The detector was calibrated before it used. The calibration is the procedure that establishes the proportionality between measured counts and ground concentrations of potassium, uranium, and thorium. Measurements of U (ppm), Th (ppm), and K (%) contents in phosphate samples. Determination of radionuclides content was based on the stripping technique of gamma-ray spectrometry.40 K content was calculated on the basis of its gamma rays at 1461 KeV and also 238 U at 1765 KeV emitted by bismuth 214 Bi and 232 Th at 2615 KeV emitted by thallium 208 Tl.
Obtained results of 238 U and 232 Th contents are referred as equivalent uranium (eU) and equivalent thorium. U and Th contents in ppm and K content in percentage were calculated into specific activities of 238 U,232 Th, and 40 K in Bq/kg using appropriate conversion factors. The specific parent activity of a sample containing 1 ppm, by weight, of 238 U is 12.35 Bq/kg, 1 ppm of 232 Th is 4.06 Bq/kg and 1% of 40 K is 313 Bq/kg. These data were used for calculation of some radiological parameters to estimate the environmental radioactivity impacts of the radionuclides.,
The absorbed dose rate is given by:,,
D (nGy/h) =5.675 U (ppm) +2.494 Th (ppm)
where 5.476, 2.494, and 13.078 are the conversion factors for U, Th, and K, respectively. Different types of radiations cause different effects in biological tissues so that we calculated the annual effective dose rate (mSv/year) using the following equation:,
H (mSv/year) = D (nGy/h) × 24 h × 365.24 × 0.2 × 0.7 × 10−6(2)
where the committee used 0.7 Sv/Gy for the conversion coefficient from absorbed dose in air to effective dose received by adults, and 0.2 for the outdoor occupancy factor.
| Results and Discussion|| |
The content (in ppm) for different nuclides (U, Th) and K% for twenty locations are given in [Table 1], in the areas of Safaga and Abu-Tartur. From [Table 1], the values of 238 U ranged from18 to 29 ppm,232 Th ranged from 5 to 14 ppm, and K% ranged from 0.4 to 1.2 for Safaga area. And also the content of 238 U ranged from 20 to 50 ppm,232 Th ranged from 10 to 26 ppm, and K% ranged from 0.5 to 1.9 for Abu-Tartur area.
|Table 1: The activity concentration (Bq/kg), content (ppm) of 238U, 232Th,40K, absorbed dose rate (D), and the annual effective dose rate (H) of the phosphate samples|
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From the results, the activity concentrations of 238 U ranged from 222.3 to 358.2 Bq/kg,232 Th ranged from 20.3 to 56.8 Bq/kg, and 40 K ranged from 125.2 to 375.6 Bq/kg in the area of Safaga. Moreover, the activity concentrations of 238 U found to be 247–617.5 Bq/kg,232 Th ranged from 40.6 to 105.6 Bq/kg, and 40 K ranged from 156.5 to 594.7 Bq/kg in the area of Abu-Tartur. The values of the annual effective dose rate and absorbed dose rate of the samples in Safaga and Abu-Tartur are shown in [Table 1]. The values of the absorbed dose rate ranged from 85.8 to 215.2 nGy/h and the annual effective dose rate ranged from 0.11 to 0.26 mSv/year for Safaga area. However, in Abu-Tartur, the values of the absorbed dose rate ranged from 147.6 to 353.4 nGy/h and the annual effective dose rate ranged from 0.18 to 0.39 mSv/year.
[Table 2] gives the values for different nuclides (U, Th) and K% for twenty locations of El-Sebaeya and Hamrawayn, respectively. The content of 238 U ranged from 14 to 55 ppm,232 Th ranged from 9 to 22 ppm, and K% ranged from 0.2 to 1.5. However, the values of the activity concentration of 238 U ranged from 172.9 to 679.3 Bq/kg,232 Th ranged from 36.5 to 89.3 Bq/kg, and 40 K ranged from 62.6 to 469.5 Bq/kg for El-Sebaeya area. The activity concentrations of 238 U,232 Th, and 40 K for Hamrawayn area ranged 61.8–333.5, 4–56.8, and 62.6–469.5 Bq/kg, respectively. From [Table 2], we find that the values of the absorbed dose rate ranged from 112.36 to 364.64 nGy/h and the annual effective dose rate ranged from 0.14 to 0.45 mSv/year for El-Sehaeya area. And also the obtained results of the absorbed dose rate ranged from 33.5 to 202.8 nGy/h and the annual effective dose rate ranged from 0.04 to 0.25 mSv/year for Hamrawayn area.
|Table 2: The activity concentration (Bq/kg), content (ppm) of 238U, 232Th, 40K, absorbed dose rate (D), and the annual effective dose rate (H) of the phosphate samples|
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From the results, it is clear that the concentrations of 238 U and 40 K are higher than 232 Th in the investigated areas. The concentrations of natural radionuclides in Abu-Tartur and El-Sebaeya are higher than Safaga and Hamrawayn. The concentrations of 238 U in El-Sebaeya are higher than Abu-Tartur. The concentration of radionuclides in Hamrawayn is lower than the investigated areas as shown in [Figure 1]. The obtained results for 238 U and 232 Th are higher than the acceptable levels of UNSCEAR  and the values of potassium (K%) are high in all locations. The composition of phosphate ores varies from one deposit to another. Therefore, phosphate rocks from different sources are expected to behave differently in acidification processes. The results of the present study shall help to determine the positions which have the highest value of phosphate ores.
|Figure 1: The comparison between the average values of activity concentrations of U-238, Th-232, K-40 for the studied areas|
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[Table 3] gives the average values of 238 U,232 Th,40 K, absorbed dose rate, and annual effective dose rate for the investigated areas. From the results, we find that the values of the annual effective dose rate and the absorbed dose rate in El-Sebaeya are higher than the other areas as shown in [Figure 2] and [Figure 3]. The average values of the annual effective dose were 0.19, 0.28, 0.29, and 0.15 mSv/year for Safaga, Abu-Tartur, El-Sebaeya, and Hamrawayn, respectively. The average values of the absorbed dose rate are equal to 153.7, 234.7, 235, and 120.6 nGy/h for the areas Safaga, Abu-Tartur, El-Sebaeya, and Hamrawayn, respectively, are higher than the permissible average world limit, which recommended by UNSCEAR  where the world average level is 57 nGy/h. Radioactivity levels depend on geological aspects of rock samples, where they are found in varying concentrations. The chemical and physical alterations play their role in the redistribution of radionuclides in different phosphate rock types which were subjected to these alteration processes. The comparison was made between the present experimental results and worldwide values. The results from present analyses were found to be in a good agreement with the published data by other workers in different countries as shown in [Table 4].
|Figure 2: The comparison between the average values of the annual effective dose of the studied areas|
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|Figure 3: The comparison between the average values of the absorbed dose rate for the studied areas|
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|Table 3: The average values of 238U, 232Th, 40K, annual effective dose rate (mSvy-1), and absorbed dose rate (nGyh-1) for the investigated areas|
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|Table 4: The comparison between the obtained average results and published results in different countries|
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| Conclusions|| |
Radioactivity levels of the environment depend on the geological aspects of rock samples, where they are found in varying concentrations. The chemical and physical alterations play their role in the redistribution of radionuclides in different phosphate rock types which were subjected to these alteration processes. This distribution of radionuclides reflects its impacts on the environment. From the results, the average values of uranium concentrations are equal to 236.1, 380.4, 396.4, and 197.7 Bq/kg and thorium equal to 42.6, 72.2, 68.6, and 32.1 Bq/kg for the areas Safaga, Abu-Tartur, El-Sebaeya, and Hamrawayn, respectively. It seems that the Hamrawayn deposit has the lowest radioactivity level of exploited phosphate of sedimentary origin. The measured values of specific activity concentrations of 238 U,232 Th series, and 40 K in surface soils of phosphate mine were found to be higher than the worldwide average concentrations of 238 U,232 Th are recommended by UNSCEAR  as 35 and 30 Bq/kg.
The average of the annual effective dose rate is equal to 0.19, 0.28, 0.29, and 0.15 mSv/year for the areas, Safaga, Abu-Tartur, El-Sebaeya, and Hamrawayn, respectively. The total annual exposure of phosphate workers to radioactive material in a closed workspace is lower than permissible average world limit, which recommended by UNSCEAR. The average values of the absorbed dose rate are equal to 153.7, 234.7, 235, and 120.6 nGy/h for the areas, Safaga, Abu-Tartur, El-Sebaeya, and Hamrawayn, respectively, are higher than the permissible average world limit, which recommended by UNSCEAR  where the world average level equal to 57 nGy/h.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4]