Evaluation of Naturally Occurring Radionuclide in Soil Samples from Erena Mining Sites in Niger State, Nigeria

Abstract

This study presents results of Activity Concentrations, Absorbed dose rate and the Annual Effective dose rates of naturally occurring radionuclides (40K, 232Th and 226Ra) in 7 soil samples collected from different areas of Erena mining sites at (indicate the name of the town here) 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 48.5226 ± 3.5770 to 1002.9550 ± 9.7978; for 226Ra it ranged from 23.2909 ± 2.2016 to 75.3187 ± 5.0984 and for 232Th the range is from 23.8312 ±2.0525 to 59.2930 ± 2.3945Bq.Kg-1. While the Absorbed Dose for 40K ranged from 2.0234±0.1492 to 33.0293 ± 0.3567 ŋGy.h-1, for 226Ra the range is from 10.7604 ± 1.3384 to 34.7972 ± 2.3555 ŋGy.h-1 and for 232Th the range is from 14.3940 ± 1.2391 to 35.8130 ± 1.4463 ŋGy.h-1. The total average Absorbed Dose rate of the 7  soil samples collected is 69.1480 ŋGy.h-1 and the estimated Annual Effective Dose for the sampled areas range from 0.0025- 0.0668 mSvy-1 (i.e 3 – 67 μSv.y-1), with an average Annual Effective Dose of 0.0848mSv.y-1 (i e 84.8 μSv.y-1). These results shows 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 [6]. Also the mean Radium Equivalents obtained ranged from 82.7770 BqKg-1 (ER4) to 171.9653 BqKg-1 (ER2). 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 0.2236 Bqkg-1 (ER4) to 0.6686 Bqkg-1 (ER2), 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 0.3191 Bqkg-1 (ER4) to 0.6681 Bqkg-1 (ER2). Finally, the mean value of the Excess Alpha Radiation (Iα) ranged from 0.1165 Bq.Kg-1 to 0.3766 Bq.Kg-1. 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 site area.