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Soil Radioactive Maps for Natural and Artificial Radionuclides and Estimation of Public Dose at East and North Bekaa – Lebanon |
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PP: 1-6 |
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doi:10.18576/jrna/050101
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Author(s) |
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Rana Baydoun,
Walid Tarraf,
Omar El Samad,
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Abstract |
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| The long-lived radionuclides, 238U, 232Th and their decay products and 40k are the major sources of radioactivity in soil. Cesium isotopes are the main artificial radionuclides deposited over soil by fallout or wet deposition. In addition, cosmic rays at ground levels are major contributor to external dose rate. In this work public dose arising from terrestrial and cosmic radiation was assessed. Sixty-five samples were collected from uncultivated areas, situated at East and North Bekaa province, cleaned, dried and prepared in the adopted counting geometry and measured by gamma spectrometer with high purity germanium detectors. The average activity concentrations of primordial radionuclides 238U, 232Th and 40K were comparable to worldwide values; 35 Bq kg-1, 30 Bq kg-1 and 400 Bq kg-1 respectively, while that of 226Ra was higher than worldwide average 35 Bq kg-1. Surface activity concentrations were deduced and radioactive maps were established using inverse distance weighted (IDW) method. The average activity concentration of the artificial radionuclide, 137Cs was found to be lower than that reported in soil samples studied at other Lebanese provinces. The average absorbed dose rate from terrestrial radiation was 65 nGy h-1 while the average annual effective dose was 79 μSv y-1, values lower than worldwide average value stated in UNSCEAR- 0.5 mSv y-1 and higher than those reported in studies carried out at other Lebanese provinces. Four stations belonging to the radiation early warning network system fixed in the studied area were used for continuous monitoring of ambient air dose rate including cosmic rays. These are composed of dose rate meters Gamma Tracer XL2 from Saphimo-Bertin, with Geiger Muller tubes. The average annual ambient gamma dose rate was 0.61 mSv y- 1, a value double worldwide value 0.3 mSv y-1. The average total annual public dose due to external exposure arising from both terrestrial radiation and cosmic rays was 690 μSv y-1, a value lower than the sum of worldwide values stated by UNSCEAR.
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