In situ natural radioactivity and radiological hazard assessments of granite gneiss outcrops in parts of the Southwestern Basement Complex of Nigeria

Radioactive emission (gamma ray) emanating from rock materials constitutes threats to humans and their environment. Hence, the natural radioactivity and radiological hazard indices of some granite gneiss outcrops with their residual soils from two different localities within the Southwestern Basement Complex of Nigeria were assessed using Gamma-ray spectrometry. The study aimed at determining the natural radiation levels of granite gneissic rocks and associated radiological threats to people living in the study area from gamma ray exposure. Data were collected along six geophysical traverses of 200 m each with station spacing of 5 m using the portable hand-held Gamma-ray Spectrometer. The results of weighted mean values of the elemental and activity concentrations for 40K, 238U, and 232Th are 2.00 ± 1.43%, 3.13 ± 0.90 ppm, 12.32 ± 4.99 ppm and 629.28 ± 447.29, 38.58 ± 11.02, 49.96 ± 20.23 respectively. The obtained mean concentration ratios of 1.32 for U/Th and 2.14 for Th/U were higher than 0.26 and lower than 3.5 global standard ratios respectively. The increase in activity concentrations and concentration ratio may have suggested the enrichment of radioactive minerals in the granite gneissic rocks. The annual outdoor and indoor effective doses of gamma ray exposure for people living in the study area were below the world permissible standard of 1 , thus, the area is radiologically safe. However, increase in estimated mean of AGDE and ELCR; 525.620 and 1.273 above the world permissible standards of 300 and respectively does not translate to significant radiological threats. Therefore, control measure by constant monitoring of the radioactivity levels of the area and rocks should be practiced.