Spatial distributions and dose assessment of natural radionuclides in rocks and soils of some selected sites in southwestern Nigeria

ABSTRACT

The activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K in rock and soil samples collected from Ondo and Ekiti States in southwestern Nigeria were measured by using gamma-ray spectrometer with a high-purity germanium (HPGe) detector. The mean activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K in the rock were 25.53, 61.12, and 554.20 Bq kg⁻¹ respectively, while that of the soil were 8.27, 17.37, and 151.72 Bq kg⁻¹ respectively. Results showed that the activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K were higher in the rocks than the soils of the areas studied. To assess the radiological impact of some radionuclides on the population in the region, the annual effective dose equivalent (AEDE), annual gonadal equivalent dose (AGED), and excess lifetime cancer risk (ELCR) were calculated. The mean values of the indoor and outdoor AEDE, and AGED were 88.08 µSv y⁻¹, 352.34 µSv y⁻¹, and 508.40 mSv y⁻¹, respectively for the rock samples, and 25.31 µSv y⁻¹, 101.25 µSv y⁻¹, and 145.80 mSv y⁻¹ respectively for the soil samples. The mean values obtained for AEDE and AGED for the soil were below ICRP recommended limits of 1 and 300 mSv y⁻¹, respectively. AGED for the rocks was higher than the maximum permissible limit.

KEYWORDS:

• activity concentration
• dose assessment
• natural radionuclides
• rocks
• soils