Natural Radioactivity Measurements and Evaluation of Radiation Hazards in Soil Samples of Shinyalu, Kakamega County, Kenya
Khabana, Echesa Malack
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Radioactive elements are found everywhere in the environment. Detectable amounts occur naturally in soil, rocks, water, air and vegetation and may be ingested if they enter the food chain, or, inhaled. Inhaled and ingested radionuclides lead to internal exposure. In addition, humans also receive external exposure due to the radioactive materials located outside the body. Primordial radionuclides 238U, 232Th and 40K are the main sources of external radiation exposure to the general public. Exposure to enhanced radiation levels for long periods of time may lead to health related problems like cancer. This research project aimed at measuring the concentration of primordial radionuclides in soil samples from Shinyalu region in Kakamega County and evaluating the radiation exposure to the local population. Twenty three surface soil samples were collected from selected locations in study area and analysed for the content of 238U, 232Th and 40K using a NaI (Tl) gamma ray spectrometer. Radiation hazard indices, external dose rates and the radium equivalent activity were calculated based on the activity concentration of the primordial radionuclides. The mean activity concentration for 238U, 232Th and 40K were; 189±9 Bqkg-1 within the range of 58±3-349±17 Bqkg-1, 151±8 Bqkg-1 within the range of 33±2-364±18 Bqkg-1 and 902±45 Bqkg-1 within the range of 98±5-1718±86 Bqkg-1 respectively. The mean values of concentration for 238U, 232Th and 40K exceeded the world average of 33 Bqkg-1, 45 Bqkg-1 and 420 Bqkg-1 respectively. The values for radium equivalent activity, external gamma hazard and internal hazard indices were; 475±24 Bqkg-1 within the range of 151±8-910±46 Bqkg-1, 1.28±0.06 within the range of 0.41±0.02-2.46±0.12 and 1.75±0.08 within the range of 0.69±0.03-3.08±0.10 respectively. The average absorbed dose rate was found to be 216±11 nGyh-1within the range 69±3 - 408±20 nGyh-1 which was below the hazard limit of 1500 nGyh-1. The annual effective dose rate was found to be 0.27±0.01 mSvy-1 within the range 0.08 - 0.50±0.03 mSvy-1 which is below the ICRP limit of 1 mSvy-1 for members of general public. These results reveal no significant radiological health hazards for inhabitants within the study area.