Natural radioactivity in surface soil of urban settlements in Ekiti State, Nigeria: baseline mapping and the estimation of radiological risks

This study was initiated to carry out a comprehensive radiological assessment of natural radioactivity in the basement complex geological areas of southwest Nigeria and to establish a baseline background radiation map for the entire area. One hundred surface soils were collected from selected urban settlements for gamma spectrometric analysis. Background radiation maps were generated for the study area using GIS-based Kriging method with Surfer 10 software. The mean activity concentrations obtained for 226 Ra, 232 Th, and 40 K in the soil samples are 24.2 ± 18.9 Bq/kg, 12.8 ± 6.2 Bq/kg, and 700.0 ± 437.4 Bq/kg, respectively. Radiological hazard parameters were calculated and average values presented as 96.4 Bq/kg (radium equivalent), 48.1 nGy/h (absorbed dose rate in air), 0.06 mSv/y (annual effective dose rate), and 2.0 × 10 −4 (excess lifetime cancer risk). The spatial spread of natural radionuclides and gamma dose rates on the radiological maps show areas with low, medium, and high background radiation values. The areas with high background radiation levels fall within the quartzite, migmatite, and granitic geology.