Natural radioactivity levels and associated radiological parameters in the soil samples from selected areas of Mutha, Kitui county, Kenya

Abstract

Natural radioactivity in the soil samples from Mutha area of Kitui County, Kenya was determined using a Na(I) Tl gamma-ray spectrometer. The study area was divided into forested, inhabited, farmlands, and bare grassland strata. Test results show that the average activity concentration of the 238U and 232Th and 40K was 31.3 ± 1.6, 41.5 ± 2.1, and 465.8 ± 23.3 Bq/kg with forested stratum reporting the highest concentration of 238U (44.4 ± 2.2 Bq/kg) and 232Th (72.5 ± 3.6 Bq/kg) while the inhabited areas had the highest concentration of 40K (620.4 ± 31.0 Bq/kg). Strata with human activities reported a high concentration of 40K suggesting the geology of the settlement area is different. Forested and inhabited areas contribute the highest average absorbed dose rates of 80.4 ± 4.0 and 76.2 ± 3.8 nGy/h, respectively, which are higher than the world average of 57 nGy/h but lower than the safe limit of 1500 nGy/h. The average indoor and outdoor annual effective dose and radium equivalent show a consistent trend with forested areas showing the highest values of 0.3 mSv/y and 172.5 ± 8.7 Bq/kg, respectively. Nevertheless, all these parameters were below the recommended safe limits, and therefore, soil from the study area is radiologically safe for use in the construction of human dwellings.