Evaluation of Naturally Occurring Radionuclide in Soil Samples from Ajiwei 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 8 soil samples collected from different areas within the Ajiwei 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 421.6174 ± 7.9316 to 768.7403 ± 7.9315; for 226Ra it ranged from 20.6257 ± 2.0858 to 44.0324 ± 5.0985 and for 232Th the ranged is from 23.7172 ± 1.3683 to 62.7137 ± 4.1049 Bq.Kg-1 . While the Absorbed Dose for 40K ranged from 17.5814 ± 0.3307 to 32.0565 ± 0.3307 ŋGy.h-1 , for 226Ra the range is from 9.5291 ± 0.9636 to 20.3430 ± 2.3555 ŋGy.h-1 and for 232Th range from 14.3252 ± 0.4414 to 37.8791 ± 2.4794 ŋGy.h-1 . The total average Absorbed Dose rate of the 8 soil samples collected is 63.7877 ŋGy.h-1 and the estimated Annual Effective Dose for the sampled areas range from 0.0636- 0.1028mSvy-1 (i.e 64 – 103 μSv.y-1 ), with an average Annual Effective Dose of 0.0782 mSv.y-1 (i.e. 78.2 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 107.3259 BqKg-1 (AJ1) to 179.4064 BqKg-1 (AJ4). 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 0.1229 Bqkg-1 (AJ3) to 0.4226 Bqkg-1 (AJ7).. 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 0.3456 Bqkg-1 (AJ1) to 0.6453 Bqkg-1 (AJ2) .Finally, the mean value of the Excess Alpha Radiation (Iα) ranged from 0.1031 Bq.Kg-1 (AJ1) to 0.2202 Bq.Kg-1 (AJ3. 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.