Gamma Ray Spectrometric Analysis of the Naturally Occurring Radionuclides in Soils Collected Along the Shores of Lake Victoria, Migori County, Kenya
Daniel, Okelo Elijah
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Natural radiation is present in all human environments: rocks, soil, water, air, food etc at varying concentrations. The major radionuclides responsible for the natural terrestrial background radiation are 40K and the radioisotopes in the decay series of 238U and 232Th .These radionuclides pose exposure risks due to their radiation which could lead to health related problems like cancer to the people exposed. There is therefore a growing concern on the health risks associated with such exposure to natural sources of radiation in the place of work. In this research sand samples from the sand mines at the estuaries of River Kuja, River Migori and other small streams in Migori County were analyzed using NaI (TI) detector together with a computer based gamma ray spectrometer. The average concentrations of 238U, 232Th and 40K in the samples analyzed in this study are 64.5±3.3 BqKg-1,146.0±4.4 BqKg-1 and 1222.8±43.3 BqKg-1 respectively. It is observed that the activity concentrations are above the world average values. As a measure of radiation hazard to the general public, the absorbed dose rate in air at a height of 1m above the ground surface was estimated. The calculated radiation absorbed dose rate from the different sampling sites ranges from 123±2.4 nGyh-1 to 236±4.8 nGyh-1 with an average of 171.2±3.4 nGyh-1. The mean value is higher than the world average of 60 nGyh-1.The annual effective dose rates were calculated for human exposure to the gamma radiations from the radionuclides; 238U,232Th and 40K in the sand samples and were found to range from 0.302±0.006 mSvy-1 to 0.579±0.012 mSvy-1 , which is below the ICRP limit of 1mSvy-1 for members of the general public. The internal and external hazard indices were calculated and their average found to be 0.99±0.02 mSvy-1 and 1.17±0.02 mSvy-1 respectively, with external hazard index being more than unity, hence slightly exceeding the permissible limits set by the International Commission on Radiation Protection (ICRP).