Assessment of environmental radiation exposure from soil radioactivity around the Southern area of Chad

A study to ascertain the radioactivity levels of various radionuclides from soil samples collected in Chad using a high-resolution gamma ray spectrometry system is presented in this article. The activity concentrations are determined for the radionuclides:226Ra,214Pb,214Bi and228Ac,208Tl,212Pb following the decay of238U and232Th as well as40K,235U, and137Cs. The values of activity concentrations of238U,232Th, and40K in the soil samples ranged from 2 to 245, 2–40, and 20–454 Bq/kg, whereas235U and137Cs ranged from 0.8 to 21.7 and 0.3–3.8 (Bq/kg), respectively. In order to evaluate the radiological exposure of the natural radioactivity, the radium equivalent activity, external exposure index, internal exposure index, and annual effective-dose equivalent have been calculated which ranged from 27 to 465 (Bq/kg), 0.09–1.25, 0.13–2.38, and 0.09–1.65 (mSv/y), respectively. Correlation between238U versus232Th,40K versus238U, and40K versus232Th was investigated; the results showed good correlation for238U versus232Th and40K versus238U while40K versus232Th gives poor correlation. For the 20 samples collected and analyzed for this study, the results showed that average activity concentration of238U is relatively higher than the world average, while for both232Th and40K, it was relatively lower.