Evaluation of naturally occurring radionuclide in soil samples from pandogari mining sites in Niger State, Nigeria

This study presents results of Activity Concentrations, Absorbed dose rate and the Annual Effective dose rates of naturally occurring radionuclides (40K, 232Th and 226Ra) absorbed in 7 soil samples collected from different areas within the Pandogari mining sites in Niger State, North Central Nigeria. A laboratory γ-ray spectrometry NaI (Tl) at the Centre for Energy Research and Training (CERT), Ahmadu Bello University Zaria, was used to carry out the analysis of the soil samples. The values of Activity Concentration for 40K ranged from 30.3266 ± 7.0295 to 259.2535 ± 6.3764 BqKg-1; for 226Ra it ranged from 17.6129 ± 3.8239 to 62.1089 ± 6.1066 BqKg-1 and for 232Th the ranged is from 21.5507 ±2.8506 to 60.4333 ± 2.0525 Bq.Kg-1. While the Absorbed Dose for 40K ranged from 1.2646 ± 0.2931 to 17.6333 ± 0.2020 ŋGy.h-1, for 226Ra the range is from 8.1372 ± 1.7666 to 28.6943 ± 2.8212 ŋGy.h-1 and for 232Th range from 13.0166 ± 1.7218 to 36.5017 ± 1.2397 ŋGy.h-1. The total average Absorbed Dose rate of the 7 soil samples collected is 52.1535 ŋGy.h-1 and the estimated Annual Effective Dose for the sampled areas range from 0.0318- 0.1016mSvy-1 (i.e. 32 – 102 μSv.y-1), with an average Annual Effective Dose of 0.0532mSv.y-1 (i.e. 53.2 μSv.y-1). These results show’s that the radiation exposure level reaching members of the public in the study areas is lower than the recommended limit value of 1 mSv.y-1 (UNSCEAR, 2000). Also the mean Radium Equivalents obtained ranged from 58.9317 BqKg-1 (PA5) to 181.0888 BqKg-1 (PA1). These results show that the recommended Radium Equivalent Concentration is ≤ 370 BqKg-1 which is the requirement for soil materials to be used for dwellings, this implies that the soil from this site is suitable use for residential buildings. The mean External Hazard Index (Hext) ranged from 0.0692 Bqkg-1 (PA5) to 0.4891 Bqkg-1 (PA1). While the maximum allowed value of (Hext= 1) corresponds to the upper limit of Raeq (370 BqKg-1) in order to limit the external gamma radiation dose from the soil materials to 1.5 mGy y-1. That is, this index should be equal to or less than unity (Hext≤ = 1). Furthermore, the mean Internal Hazard Index (Hext) ranged from 0.0453 Bqkg-1 (PA3) to 0.6569) Bqkg-1 (PA1) .Finally, the mean value of the Excess Alpha Radiation (Iα) ranged from 0.0881 Bq.Kg-1 (PA4) to 0.3105 Bq.Kg-1 (PA1). All these values for Iα are below the maximum permissible value of Iα=1 which corresponds to 200 Bq.Kg-1. It can therefore be said that no radiological hazard is envisaged to dwellers of the study areas and the miners working on those sites area.