EG0700180 5th Conference on Nuclear and Particle Phyilcs 19 - 23 Nov. 2005 Cairo, Egypt INTER-COMPARISON STUDY OF THE POPULATION DOSE DUE TO GAMMA-RADIATION IN THE COAST OF NORTH SINAI BETWEEN RAFAH AND SIR EL-ABD AREAS M.K. Seddeek1, T. Sharshai* H.M. Badran3'4 'Department of Physics, Faculty of Education, Suez Canal University, Al-Arish, Egypt 2Department of Physics and Chemistry, Faculty of Education, Tanta University, Kqfr El-Shaikh, Egypt 3Department of Physics, Faculty of Science, Tanta University, Tanta, Egypt 4 Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, P.O. Box 97, Amado, AZ 85645, USA ABSTRACT This study compares the external dose due to the y-ray emitting radionuclides in various areas in north Sinai, Egypt. The whole area was divided into 10 regions. The average absorbed dose rates were evaluated for each region. It was found that Zaranik protected area and Al-Massaid have the highest values of 69.0 and S4.7 nGy h"1, respectively. The corresponding values of the remaining regions were below 21 nGy h"1. The mean annual effective dose equivalent for the four largest cities Rafah, El-Sheikh Zuwaied, Al-Arish and Bir El-Abd were 20.7,16.1,53.4 and 13.9 jiSv. That is one individual at risk due to the radiation exposure of naturally occurring radionuclides in 50.8, 84.7, 8.7 and 85.3 years -for these cities, respectively. The results are compared with those from different areas in Egypt and in various countries. Keywords: Naturally occurring radionuclides, Dose rate, Radiation hazard indices, Coastal environment, Black sand, Sinai, Egypt. 1. INTRODUCTION Natural radiation is the largest contributor to the external dose of the world's population [1]. Terrestrial radiation arising fromth e Earth's crust and building materials gives rise to the external exposure and inhalation or ingestion of natural radionuclides. The most important source of external radiation exposure is due to y-rays emitted from -481 - * the ,XU and 232Th decay chains and The radiological implication of these radionuclides is due to the y-ray exposure of the body and irradiation of lung tissue from inhalation of radon and its daughters. Knowledge of the distribution of radionuclides is an essential prerequisite for : evaluation and control of public exposure. It enables one to assess any possible radiological risks to human health. The assessment of the y-radiation dose from natural sources is of particular importance for public health. To evaluate the terrestrial y-dose rate for outdoor occupation, it is very important to estimate the natural radioactivity level. The hazard due to y-rays was assessed by calculating radium equivalent, Raeq, according to [2], Raeq = Cru + 1 -43 Cjh + 0.077 CK (1) 226 232 40 where Cr8, On, and Ck are the activity concentrations of Ra, Th and K, respectively. This index is defined for comparison of the activities of the materials containing different concentrations of radionuclides. The assumed criteria are that 1 Bq kg1 of 226Ra, 0.7 Bq kg1 of 232Th or 13 Bq kg1 of'"'K produces the same y-ray dose rate and that the Ra^ should not exceed a maximum of 370 Bq kg'1 [3]. The absorbed dose rate D (nGy h'1) in outdoor air is calculated at a height of 1 meter above the ground surface for different sites. The formula used [4] is given by, 1 D = 0.462 Cu+ 0.604 C77, + 0.0417 CK (nGy h" ) (2) MA 1 where Cu is the activity concentration of U. By assuming a ratio of 0.72 Sv Gy" for absorbed dose in air to effective dose in the human body [1] and outdoor occupancy factors of 0.2, the effective dose equivalent was also calculated [1]. In order to evaluate the population dose due to outdoor y-radiation, the annual collective effective dose equivalents, Se, in the study area were assessed according to [5], ,Se=HXN (3) where H is the mean annual effective dose equivalent and N is the estimated population of the studied area. Considering Rk, the risk factor, 1.65 *10"2 Sv*1 [6], the collective health detriment G is given by G = RKXSE (4) The objective of the present study is to estimate and compare the radiological hazards due to radioactivity contents of sand samples from various locations in north Sinai and to assess any health risks. -482- 2. STUDY AREA AND EXPERIMENTAL PROCEDURES Sinai Peninsula lies in the northeast of Egypt The area under study is located in the north of Sinai along the Mediterranean coast (Fig. 1). The first study [7] covered a region (referred to as region 1) which extends for about 40 km along the coast line. The eastern and western limits of region I were 8 km east and 32 km west (the Zaranlk protected area) of Al-Arish city. Region I encompassed a total area of about 150 km2. Hie second study [8] covered, two regions; the eastern region (region II) extends from the eastern limit of region I west (8 km east Al-Arish city) to Rafah city east and the western region (region III) extends from the Zaranik protected area east (western limit of region I) to Bir El-Abd city west The whole area included in both studies (—650 km2) is situated between East longitudes 33° 00' and 34° 17' and North latitudes 31° 00" and 31° 20'. 100 sample locations were included in both studies. For the purpose of comparing the general public's external exposure dose, the whole area was divided into 10 local regions (R1,R2 ... and R1Q in Fig. 1). The division is based on geographic conditions and political divisions. A description of the sampling methods and sample preparations can be found elsewhere [7]. The activity concentrations of the samples were tneasured using a 204 cm3 p-type HPGe detector (Tennelec) with a relative efficiency of 50%. The details of the calibrations of the detecting system and the activity concentration measurements are found in Refs. 7-10. 3. RESULTS AND DISCUSSION 3.1 Sand characteristics and activity concentrations Sand samples in the 10 regions are weak base with the same mean pH value of ~8.0. The total organic matter (TOM) content was found to be less than 1% for all samples. No significant correlation between ibe sand characteristics and any of the sample activity concentrations was found. The results of the activity concentration measurements [7,8] indicate that the activity concentrations of 7,26Ra and mTh in some locations in Al- Massaid (R4) and the Zaranik priftected areas (R3) were high compared with those in other locations. The rest of the 8 areas have little variations and low concentrations (<20 Bq kg1) for their ~r'Ra and 232Xh activities with Only one exception (beach site) with activities 46.5±0.6 and 68.1±1.3 Bq kg"1, respectively [8]. 3.2 Dosimetry The calculated radium equivalent, absorbed dose rate in outdoor air at a height of 1 meter above the ground surface and effective dose rate 'due to the presence of the natural radionuclides in the sand are given for the 10 local regions in Table 1. The highest 1 average values of Raoq were 170.8 and 138.0 Bq kg" in the Zaranik protected area (R3) and Al-Massaid (R4), respectively. Also, both areas showed a wide range of Ra^, values 483 - 31° 10' 00' 09 4* Fig. 1. The map of the study areas, showing the 100 sampling locations, North Sinai. The locations included in region I [7] are marked with a closed box, while those represented by open triangles are corresponding to the two others II and III [8]. The 10 local regions are; RI Bir El-Abd, R2 EI-Mazar, Et-Telol and Misfaq, R3 Zaranik, R4 Al-Massaid, R5 Al- Arish, R6 Al-Arish valley, R7 El-Kharruba and As-Sakaska, R8 El-Sheikh Zuwaied and Esh-Shalak, R9 Al-Ahrash and Saladin and R10 Twyiel AI-Amir and El-Masora. compared with the ranges of others. The high Ra^ values are due mainly to the high concentrations of 226Ra and 232Th in the sand samples of both areas because of the existence of black sand. The calculated values of Ra«, for all 10 regions were cleanly lower than the recommended limit of 370 Bq kg"1 [3]. Three local regions, Al-Arish (R5), Twyiel Al-Amir and EI-Masora (RIO), and El-Kharruba and As-Sakaska (R7), have nearly the same value of —45 Bq kg"1. The remaining 5 regions have nearly the same Ra^ values (<28.5 Bq kg"1). Table 1. The average and range of the radium equivalent, absorbed dose rate and effective dose equivalent for the 10 local regions. The total number of beach sand (bs) or dune sand (ds) locations included in the calculations in each regions are given. No. of Region Raeq Dose rate Eff. D. eq. Region locations No. Bqkg"1 nGy h"1 HSv a"1 (bs,ds) R1 Bir El-Abd (1,8) 26.9±4.5 12.5±4.2 15.7±4.8 (15.6-47.3) (7.7-20.8) (9.7-26.3) R2 El-Mazar, Et-Telol (0,6) 19.7±3.5 8.8±3.0 11.2±3.4 & Misfaq (14.2-23.7) (5.9-10.4) (7.4-13.2) R3 Zaranik (5,9) 170.8±11.4 69.0±13.6 87.1±17.0 (12.0-990.2) (5.3-387.9) (6.7-489.7) R4 Al-Massaid (8,2) 138.0±8.3 54.7±10.3 69.0±12.9 (17.6-428.7) (8.9-165.5) (11.2-208.9) R5 Al-Arish (9,5) 50.3±6.4 20.8±7.3 26.3±9.0 (14.1-154.4) (7.7-68.5) (9.7-86.4) R6 Al-Arish valley (0,4) 28.4±3.2 17.1±2.9 21.6±3.2 (26.9-31.3) (11.4-21.6) (14.3-27.2) R7 El-Kharruba & (5,5) 41.7±5.8 18.2±6.2 22.9±7.6 As-Sakaska (15.3-148.8) (7.3-61.4) (9.2-77.5) R8 El-Sheikh Zuwaied (4,9) 27.7±5.5 12.5±5.5 15.8±6.5 & Esh-Shalak (10.4-44.8) (4.6-20.2) (5.8-25.5) R9 Al-Ahrash & (1,9) 25.1±4.2 12.9±4.3 16.2±4.9 Saladin (17.9-49.3) (7.9-21.2) (9.9-26.7) R10 Twyiel Al-Amir ~(0,10) 45.2±5.2 19.9±4.4 25.1±5.0 &El-Masora (35.9-50.3) (15.8-22.3) (20.0-28.2) The highest average absorbed dose rates were 69.0 and 54.7 nGy h"1 for the Zaranik protected area and Al-Massaid, respectively.