Occupational Exposures during the U-Exploration Activities at Seila Area, South Eastern Desert, Egypt

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1 Arab Journal of Nuclear Science and Applications, 50 (2), (-29) 207 Occupational Exposures during the U-Exploration Activities at Seila Area, South Eastern Desert, Egypt Y.A. Abdel-Razek a, M.S. Masoud a, M.Y. Hanfi a and M.S. El-Nagdy b. (a) Nuclear Materials Authority, Cairo, Egypt. (b) Physics Department, Faculty of Science, Helwan University, Cairo, Egypt Received: 0/3/206 Accepted: 0/4/206 ABSTRACT Twenty trenches distributed over a shear zone at Seila area, South Eastern Desert of Egypt were chosen to study the occupational exposures during the U-exploration activities in these trenches. The average value of the activity concentration of 238 U, 232 Th and 40 K in the studied granites are 866, 57 and 380 Bq.kg - respectively. These values are higher than the worldwide average of 33, 45 and 42 Bq/kg. According to these activity concentrations, trenches are divided into the non-regulated and regulated categories. The average value of the annual effective dose due to the terrestrial radionuclides is msv for the non-regulated trenches and msv for the regulated trenches corresponding to the absorbed dose rate 29 ngy.h - for the non-regulated trenches and 684 ngy.h - for the regulated trenches. The average measured annual effective dose for non-regulated and regulated trenches is 0.8 and.42 msv respectively. This difference is ascribed to the geometry of the studied trenches. However, the total annual effective dose in the non-regulated and the regulated trenches is lower than the recommended value of 20 msv. Keywords: Occupational exposures-u-exploration-annual effective dose INTRODUCTION The granite at Gabal El Seila area is represented by Gabal Qash Amir, Gabal El Seila, and isolated granite stocks. These rocks are affected by ENE-WSW shear zone and sub-parallel fault system dipping 50º-70º to the south and extending about 9km. with thicknesses ranging between 2 to 40m. The granite, which hosted these trenches, is highly weathered, cavernous and exposed as low hills. It is coarse-grained, pink to pinkish gray in color. It is mainly composed of quartz, K-feldspar, plagioclase, biotite and rare muscovite. It is characterized by the presence of iron and manganese oxides filling joints and fractures indicating the enrichment of this granite by iron and manganese mineralization. This granite is also enriched in altered pyrite, which is sometimes leached out leaving cubic vugs and patches of deep red color. This granite is intruded by fine-grained granite which occurs as sheets and dykes trending NW-SE. This fine-grained granite is mainly composed of quartz, K- feldspar, plagioclase, biotite and muscovite and characterized by the presence of extremely abundant manganese oxides filling joints and fractures. This granite is also dissected by basic dykes. They are massive, fine-grained and gradually range in color from grayish green to dark gray, mostly having ENE-WSW trend which are usually injected along the extension planes. The southern part of the coarse-grained granite is dissected by barren quartz vein trending ENE-WSW and extend for more than 600 meters and the widest parts range from meter to 0 meters (). The extraction and processing of radioactive ores are carried out in a number of countries throughout the world. The extractive industries include all forms of mining. Minerals and other natural materials, that are not normally regarded as being radioactive, may nevertheless contain significant Corresponding author m.nuc202@gmail.com

2 Arab Journal of Nuclear Science and Applications, 50 (2), (-29) 207 levels of natural radionuclides from the uranium and thorium decay chains. The main potential sources of occupational exposure in most mining operations are the natural radionuclides arising from the radioactive decay the 238 U and 232 Th series. Exposures may arise via three main routes (2) : - The inhalation of radon, thoron and their respective progenies. 2- The inhalation and ingestion of ore dust. 3- External irradiation with gamma rays. The Egyptian Nuclear Materials Authority (NMA) established some of projects to explore the radioactive elements in Egypt. One of them was established at Seila area. So, there is a radioactive exposure for many workers in these projects from terrestrial radioactive elements such as uranium, thorium, potassium and radon. The present research was undertaken with principal goal to estimate the annual effective doses from different radioactive sources and to evaluate these effective doses under that recommended by the relevant authorities. EXPERIMENTAL Methods and Experimental Techniques Field Works Gabal El Seila area, South Eastern Desert of Egypt is located between latitudes N and longitudes E (Fig. ) at a distance of about km southwest of Abu Ramad City (3). Fig.(): Geological map of Seila area, south Eastern Desert, Egypt (3) In the U- project at Seila, twenty trenches area constructed along Seila shear zone, (Fig.). These trenches were dug to evaluate the activity concentration of the important radionuclides; uranium and thorium.

3 Arab Journal of Nuclear Science and Applications, 50 (2), (-29) 207 Fig. (2): Google image showing the locations of mechanical trenches at G. El Seila area, South Eastern Desert, Egypt Exposure inside Exploration Trenches at Seila Area Measurements of Uranium, Thorium and Potassium Concentrations Inside each trench, a portable RS-230 Gamma-Ray Spectrometer (024 channels) was used to determine the uranium, thorium and potassium concentration in the rocks of this trench. The RS-230 depends on a 6.3 in 3 (03 cm 3 ) higher density Bismuth Germanate Oxide (BGO) detector. Direct readings of the uranium, thorium and potassium concentration in (ppm) were recorded at different locations inside each trench (4). The uranium, thorium and potassium activity concentration was obtained using the conversion factor of (2.35, 4.07, 33) Bq/kg 238 U/l, 232 Th/l ppm and 40 K/l % of uranium, thorium and potassium respectively (5). Measurements of Gamma Effective Dose in Trenches at Seila Area The RDS-00 survey-meter, ALNOR, Turku, Finland, was used for measuring the γ-ray dose rate at different locations inside each trench. This survey-meter contains Geiger Muller tube calibrated by a 60 Co γ-source of activity 7.4 x0 8 Bq at the National Institute of Standards and Technology (NIST). The direct measurements were recorded. Measurements of Radon and Thoron Gases The RTM-688 device used to measure the radon and thoron concentrations by counting α-particles by radon and thoron decay products inside the chamber of the device at each trench. Inside each trench, an air sample was withdrawn through a filter by a RTM 688 radon monitor. Radon or thoron gas concentration (Bq/m 3 ) in the air at this trench is displayed on the radon monitor after one hour. RESULTS AND DISCUSSION Darnley (6) defined the "uraniferous granites" as those containing at least twice the Clarke value (4ppm U), hence, they would contain 8ppm or more, regardless of the presence of associated U- mineralization or not. Accordingly, the data in Table (), suggest that the studied granites can be considered uraniferous granites. Accordingly, the U-content in the rocks extending along the shear zone at Seila area justifies the deeper exploration activities at this area.

4 Arab Journal of Nuclear Science and Applications, 50 (2), (-29) 207 Table (): Uranium and thorium contents (ppm) and potassium content % in the granitic rocks along the shear zone at Seila area Trench number U ppm Th ppm K % Trench number U ppm Th ppm K % Activity Concentration in the Granitic Rocks at Seila Area The International Commission on Radiological Protection (7) (ICRP) recommended that the effective dose resulting from any occupational activities dealing with radioactive materials should not exceed 20mSv/y. However, the International Atomic Energy Agency (8) (IAEA) established a value of the activity concentration of a radioactive material below which it is usually unnecessary to regulate this material. For the radioactive materials of natural origin, this value is 0 Bq/g for 40 K and Bq/g for all other radionuclides of natural origin. Table.2 represents the activity concentrations of A U, A Th and A K, (Bq.kg - ) of the radionuclides 238 U, 232 Th and 40 K in the rocks at the studied U-exploration trenches. Also, the total activity concentrations in the granites at the trenches are represented in this table. The activity concentration of A U ranged from 47 Bq.kg - to 26 Bq.kg - with mean average 866 Bq.kg -. The activity concentration of A Th ranged from 24 Bq.kg - to 26 Bq.kg - with mean average 57 Bq.kg - and the activity concentration of A K ranged from 808 Bq.kg - to 593 Bq.kg - with mean average 380 Bq.kg -. The total activity concentration applied to Eq. (5) ranged from 277 to 8 Bq.kg - with mean average 467 Bq.kg -. Table (2): Activity concentrations of A U, A Th, and A K, (Bq.kg - ) and the total activity concentration A T at granites from trenches at Seila area Trench number AU Bq.kg - ATh Bq.kg - AK Bq.kg - Trench number AU Bq.kg - ATh Bq.kg - AK Bq.kg Average for all 20 trenches

5 Arab Journal of Nuclear Science and Applications, 50 (2), (-29) 207 From Table (2), it is clear that the activity concentrations of both thorium, A Th, and potassium, A K, are below the IAEA condition while the concentration of uranium, A U, divides the studied trenches into two groups; the excluded (non-regulated) group which includes trenches number,3,5,6,7,0,2,5,8,9 and 20 and the regulated group which includes trenches number 2,4,8,9,,3,4,6 and 7. The occupational exposures resulting from the U-exploration activities at the regulated trenches will be evaluated to get the necessary recommendations. However, the exposures from the non-regulated trenches will be evaluated for comparison. External Exposure We focus on the external exposure from the gamma rays evaluated by the absorbed dose rate and the effective dose rate. Absorbed Dose Rate and Effective Dose The absorbed dose related to natural radionuclides can be calculated from the following equation. (6) : D= 0.429AU ATh AK () where A U, A Th and A K are the mean activities of 238 U, 232 Th and 40 K in (Bq/kg), respectively. To estimate the effective dose from the absorbed dose, UNSCEAR (9) proposed a conversion factor (0.7 Sv.Gy - ). However, in this study a conversion factor of unity is used as well be explained below. For simplicity, the absorbed dose rate D (ngy.h - ) at m from the surface of the granitic side of a U-exploration trench is calculated by Equation (). This equation is based on the assumption that exposure to the gamma rays comes from one semi-infinite source from the ground. In fact, a worker in an exploration trench is exposed to the gamma rays from the bottom of the trench and four sides. Accordingly, the absorbed dose rate is dependent on the design of the trench and the distance of the worker from each of these sides. Since the external exposure in a studied trench effects the whole body of a worker, the factor to convert the absorbed dose rate D to effective dose rate E D equals one. So, the effective dose rate E D (nsv.h - ) equals numerically the absorbed dose rate D (ngy.h - ) or: ED (nsv.h - ) = D (ngy.h - ) (2) A survey meter that measures the external effective dose rate in a trench actually sums the effective dose rates from all sides of the trench at the location of the worker. Accordingly, the annual effective dose is calculated as follows: ED (msv.y - ) = D (ngy.h - ) x 2000h.y - x (Sv.Gy - ). (3) However, this study suggests a geometry factor (g) which is the ratio between the measured effective dose rate E m and the estimated effective dose rate E D : g = Em/ED (4) where E m = the measured effective dose rate (nsv.h - ), E D = the estimated annual effective dose rate (nsv.h - ) by Equation (3). The annual external effective dose E ex (msv.y - ) received by a worker in an U-exploration trench at Seila area is calculated assuming 2000 working hours in one year: Eex = Em x 2000 msv.y - (5) Table (3) represents the average effective dose rate; estimated E D and measured E m, the average value of the geometry factor (g) and the average annual effective dose in the non-regulated and the regulated trenches along with a box cut.

6 Arab Journal of Nuclear Science and Applications, 50 (2), (-29) 207 Table (3): Average E D (nsv.h - ) and E m (nsv.h - ). The average annual external effective dose E ex,m (msv) and the average value of (g) in the non-regulated, regulated trenches and a box cut at Seila area. Group ED nsv.h - Em nsv.h - g Eex msv.y - Non Regulated Regulated Box cut From the table, the average value of the annual external effective dose E ex, in the regulated trenches is higher than that in the non-regulated trenches. However, E ex, in the regulated trenches is lower than the reference dose, 3 msv.y - (0). Although E ex, in the box cut is lower than the recommended dose limit of 20 msv.y -, it is still higher than the reference dose. From Table (3), it is clear that the higher value of E ex, m is associated with the higher value of the geometry factor g, both in the box cut. From the description above, the higher values of g mean that the worker moves more closely to the gamma source, the trench sides i.e the dimensions of the trench were narrow. So, to decrease the values of E ex, m, the values of g must be small. Accordingly, the dimensions of the U-exploration trenches should be a wide as available. Internal exposure Concentrations of Radon and Thoron Gases Table (4) represents the average concentration of radon gas C Rn (Bq.m -3 ) in the air of the U- exploration trenches and the box cut at Seila area. From the table, both C Rn and C Tn have higher values in the box cut. Again, this is because of the narrow dimensions of the box cut which increase the ratio (surface / volume). Accordingly, increase the concentration of these radioactive gases. Table (4): Average concentration of radon C Rn (Bq.m -3 ) and thoron C Tn (Bq.m -3 ) and the relevant annual effective doses E Rn (msv)and E Tn (msv) and the total annual effective dose E T (msv) in the U-exploration trenches and the box cut at Seila area. Group CRn Bq.m -3 ERn msv.y - CTn Bq.m -3 ETn msv.y - ET msv.y - Non-Regulated Regulated Box cut Indeed, the concentrations of radon and thoron gases are much below the recommended concentrations for the occupational workers of 500 and 700 Bq.m -3, respectively. Effective Dose Due to Radon And Thoron The effective doses due to the inhalation of radon gas Rn, thoron gas Tn and their decay products are calculated assuming the mode of outdoor exposure i.e., the value of the equilibrium factor between the parent gas and its decay products chosen to be 0.4 and 0.0 for radon and thoron respectively and the occupancy time is 2000h /y and the conversion factors to obtain the effective dose from radon and thoron are 9 nsv (Bq h m -3 ) - and 40 nsv (Bq h m -3 ) - respectively. Accordingly, the annual effective doses E Rn and E Tn (msv) received by the workers due to the inhalation of radon and thoron gases and their decay products in granites trenches at Seila area calculated respectively as follows: (9)

7 Arab Journal of Nuclear Science and Applications, 50 (2), (-29) 207 Radon CRn (Bq.m -3 ) x 0.4 x 2000h x 9nSv (Bq h m -3 ) - (6) Thoron CTn (Bq.m -3 ) x 0.0 x 2000h x 40nSv (Bq h m -3 ) - (7) The average values of E Rn and E Tn are represented in Table (4). It is clear that the radon gas adds a small value to the annual effective dose while thoron gas adds negligible values compared to the effective doses from the external exposure to gamma rays. Total Effective Dose The total annual effective dose E T (msv) is the sum of the annual effective dose received from all the studied modes of exposure: ET = Eex, m+ ERn + ETn - Eout (9) E out is the annual outdoor effective dose (0.366 msv) which represents the background exposure at Seila area. From Table (4), it is clear that the average value of E T (msv.y - ) in the non-regulated trenches is lower than the recommended value for the members of public, msv.y -, (7). The average value of E T in the box cut is much higher than the reference dose indicating the need of an action to decrease the occupational exposure either by the adjustment of the working hours or by changing the design by widening the dimension of the box cut in order to meet ALARA principle. CONCLUSION The activity concentration of uranium, thorium and potassium is higher than the average worldwide. The measured gamma annual effective dose results are different for the estimated gamma annual effective dose in the regulated trenches due to the geometry for these trenches that depends on the depth of trenches. The annual effective dose that resulted from all radiation sources in these trenches is lower than the average worldwide value 20 msv. REFERENCES () M. E. Ibrahim, A. A. Zalata, H. S. Assaf, I. H. Ibrahim and M. A. Rashed, Egy. J. of Geol. 42, , (2003). (2) UNSCEAR. Sources effects and risks of ionizing radiation, Report to the General Assembly, With Annexes, United Nations Scientific Committee on the Effects of Atomic Radiation, New York, United Nations. (2008). (3) Ali and K.G.Sherif. Arabs. Geoscience (20). (4) Terraplus, sein on at 7:00 pm, (203). (5) IAEA, Radiation Safety and Protection in the Field of Radioactivity Ores Prospection, Exploration and Mining. Project: EGY/9/02-0 Egypt, pp (96-236) (989). (6) Darnley. A. G, (982). Hot granites some general remarks. In " Uranium in granites ", Maurice, Y. T, ed., Proceedings of a workshop held in Ottawa, Ontario, November, 982, Geol. Surv. Canada, paper 8-23, 2-0. (7) ICRP, (99): 990 Recommendations of the International Commission on Radiological Protection. International Commission on Radiological Protection. ICRP Publication No. 60, Pergamon Press, Oxford and New York.

8 Arab Journal of Nuclear Science and Applications, 50 (2), (-29) 207 (8) IAEA, (2004b): Workplace Monitoring For Radiation And Contamination. International Atomic Energy Agency, IAEA, Vienna, 2004 IAEA-PRTM- (Rev. ). (9) UNSCESR,: Sources and Effects of Ionizing Radiation. Volume I: Sources; Volume II: Effects. United Nations Scientific Committee on the Effects of Atomic Radiation, 2000 Report to the General Assembly, with scientific annexes. United Nations sales publication E.00.IX.3 and E.00.IX.4. United Nations, New York. (2000). (0) ICRP, (2007): The 2007 Recommendations of the International Commission on Radiological Protection International Commission on Radiological Protection. ICRP Publication No. 03, Pergamon Press, Oxford and New York.