Determination of Residential Soil Gas Radon Risk Indices Over the Lithological Units of a Southwestern Nigeria University

Radiation dose from natural sources is mainly from exposure to radon in the environment. Radon has its origin from uranium-bearing bedrocks and overburden. In the present study, assessment of the level of radon over the three lithological units upon which the residential areas of ObafemiAwolowo University Campus, Ile-Ife (OAU) was situated was carried out. Soil gas radon concentration measurement was carried out at a constant depth of 0.80 m across the three lithologies (granite gneiss, grey gneiss and mica schist) using a RAD7 electronic radon detector. A total of 138 in-situ soil gas radon measurements were carried out. Obtained experimental data were analysed and summarised using descriptive and inferential statistics with statistical significance set at p < 0.05. A radon potential map was also developed using existing permeability data of the soils in the area. Soil radon concentration varied across the different lithologies ranging from 0.04 kBq/m(3) – 190 kBq/m(3) with a mean value of 14 kBq/m(3). The mean value of Rn-222 concentration obtained in the three lithologies are 3.5 ± 5.9, 11.5 ± 25.8 and 28.4 ± 37.4 kBq/m(3) for granite gneiss, grey gneiss and mica schist respectively. There is a statistically significant difference (p < 0.001) in the mean concentration of radon-222 measured on the three lithologies. The granite gneiss and grey gneiss lithologies have been designated into low radon index, while mica schist lithology has been designated as medium radon index. 34% of the sampled areas exhibit high radon risk based on Swedish risk criteria, thereby warranting protective actions.