Analysis of Natural Radioactivity Levels and Radiation Hazards due to Murram Quarried in Kakamega County, Kenya
Luke, Songa Kamwani
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Exposure to ionizing radiation from 40K and those in the decay chains of 238U and 232Th for a prolonged time poses danger to human population. While 238U, 232Th and 40K are universally present in rock and soil, their concentration levels are not uniformly distributed. Rock and soil serve as building materials in many parts of the world and therefore can act as important sources of radiation exposure. Murram results from weathering of rocks and d espite its mining and use in construction, research on its radionuclide concentration was previously absent absent. 25 samples of murram were collected through random sampling in Malava sub county of Kakamega for measurements of radioactivity of 226Ra, 232Th and 40K. Activity concentration of 226Ra, 232Th and 40K was measured using NaI(TI) gamma ray spectrometer. The concentration obtained was used to calculate; absorbed dose, annual effective dose rate, radium equivalent activity, external and internal gamma hazard indices. The mean activity concentration for 226Ra, 232Th and 40K obtained were; 200±10 Bqkg-1 within the range of 19±1-318±16 Bqkg-1, 80±4 Bqkg-1 within the range of 11±1-194±10 Bqkg-1 and 968±48 Bqkg-1 within the range of 79±4-1965±98 Bqkg-1 respectively. The mean values of activity concentration for 226Ra, 232Th and 40K exceeded the world average of 33 Bqkg-1, 45 Bqkg-1 and 420 Bqkg-1 respectively. The average dose rate was found to be 180±9 nGyh-1 within the range 66±3-263±13 nGyh-1 which is below the hazard limit of 1500 nGyh-1but above world’s average of 55 nGyh-1. The indoor and outdoor annual effective dose rate was found to be 0.88±0.04 mSvy-1 within the range of 0.32±0.2-1.29±0.06 mSvy-1 and 0.22±0.011 mSvy-1 within the range of 0.08±0.04-0.32±0.02 mSvy-1 respectively. These health hazard parameters were below the safe limit of 1.0 mSvy-1 but above world’s average of 0.07 mSvy-1(UNSCEAR, 2016). The mean values for radium equivalent activity, external and internal gamma hazard indices were; 390±19 Bqkg-1 within the range of 144±7-596±30 Bqkg-1, 1.05±0.05 within the range of 0.39±0.02-1.61±0.08 and 1.60±0.08 within the range of 0.44±0.02-2.36±0.12 respectively. The average for radium equivalent activity exceeded the world’s average of 89 Bqkg-1 and acceptable limit of 370 Bqkg-1 and for external and internal gamma hazard indices slightly exceeds the world’s average and safe limit of 1. These results reveal insignificant radiological health hazards for inhabitance within the study area hence murram is safe for use and also safe for quarriers.