Radioactivity Assessment of 40K, 238U and 232Th in Surface Soil Samples of Igbokoda, Southwest of Nigeria

Abstract

Natural radionuclides are found in soil and are capable of disintegrating leading to the release of ionizing radiations that can have harmful effects on individuals exposed to them most especially when exceeding the recommended global limits of radiological parameters. Assessment of activity  concentrations of ⁴⁰K, ²³⁸U and ²³²Th in surface soil samples from different locations  at Igbokoda where crude oil exploration was taking place, at Ondo State in Nigeria, had been determined by gamma spectrometry using NaI (TI) detector coupled with a pre-amplifier base connected to a multiple channel analyzer (MCA) which was used to calculate the radiological indicators. 10 samples were collected from the study area putting into consideration the densely populated parts where crude oil exploration and drilling its wells were taking place. The mean activity  concentrations of ⁴⁰K,  ²³⁸U and ²³²Th obtained from the soil samples were 494.64 ± 10.46 , 19.76 ± 3.09 and 31.98 ± 5.10 Bq kg^–1_,respectively. The mean external hazard index (H_ex) and mean internal hazard index (H_in) for all the soil samples were 0.2836 and 0.3370, respectively, while the mean radium equivalent activity was 104.92 Bq kg^–1. The mean absorbed dose rate value was 49.68 nGy hr^–1 with mean annual effective dose equivalent of 0.0610 mSv yr^–1. The mean excess lifetime cancer risk for outdoor exposure was 0.2132 x 10^–3. The values of the radiological parameters: mean external and internal hazard indices, mean radium equivalent activity, mean absorbed dose rate, mean annual effective dose equivalent and mean excess lifetime cancer risk were within the recommended limits of 1.0 Bq kg^–1, 370 Bq kg^–1, 55.00 nGy hr^–1, 1.0 mSv yr^–1 and 1.45 x 10^–3, respectively.

Keywords:  Activity concentration, Exposure, Health implication, surface soil