Studies of the Terrestrial outdoor Gamma Dose Rate Levels in Ogun-Osun River Basins Development Authority Headquarters, Abeokuta, Nigeria

Problem statement: The natural radioactivity levels in the soils of Ogun-Osun River Basins Development Authority Headquarters, (O-ORBDA HQ) Abeokuta, South-Western part of Nigeria were measured. Approach: (O-ORBDA HQ) is a parastatal of Federal Ministry of Water Resources and Rural Development in Nigeria charged with the responsibility for the development and management of the water resources in its area of coverage. The area of the site was divided into fifteen segments and soil samples were collected at a depth of about 10cm at the intersection of these lines. Results: Global Positioning System (GPS) was used to obtain the geographical position of each sample point. NaI (Tl) scintillation detector coupled with a Canberra series 100 plus MCA was used as the detecting device for the gamma scintillation spectroscopy. The average activity concentrations obtained for the three radionuclides were 896.12±274.48 Bq kg^-1 for ⁴⁰K, 13.93±2.36 Bq kg^-1 for ²³⁸U and 18.67±5.06 Bq kg^-1 for ²³²Th. The average values of the absorbed dose rates in air of each radionuclide were found to be 37.64±11.53 nGy h^-1 for ⁴⁰K, 5.98±1.10 nGy h^-1 for ²³⁸U and 12.44±3.37 nGy h^-1 for ²³²Th. Conclusion/Recommendations: The baseline average outdoor annual effective dose equivalent in O-ORBDA HQ due to the radioactivity concentrations was found to be 68.74±19.51 μSv year^-1. This value is less than the world average of 70 μSv year^-1 specified by UNSCEAR for an outdoor effective dose. Hence the probability of occurence of any of the health effects of radiation is low. Since no artificial radionuclides was detected, this represents the baseline value of natural radioactivity.