MEASUR_EMENT OF NATURAL RADIOACTIVITY OF SOILS FROM SELECTED CITIES IN OYO STATE, SOUTHWESTERN NIGERIA

Abstract

The concentrations of some of the natural radionuclides in the uranium, actinium and thorium series and of4oK in soil samples collected from 9 major towns of Oyo State, Southwestern Nigeria have been determined by gamma ray spectrometry (using high purity germanium detector). Spectral analyses were performed with the Genie2k spectrometry software, version 2.1 (Canberra Industries Inc.). A library of radionuclides, which contained the energy of the characteristic gamma peaks for each nuclide analysed and their corresponding emission probabilities were built from the data supplied in the software. The natural radionuclides that were discovered in the soil samples includes, 4°K, 208TI,. 2loPb, 212Bi, 212Pb, 214Bi, 214Pb, 224Ra, 226Ra, 228Ac, 228Th 234Mp 234Th d 235U 137C h I ifici I di lide , a, an . s was t e on y arti icia ra ionuc I e froun d iIn trace form in some of the samples analysed. The specific activities ranged from -0.102 ± ). 0.29 for 137CSto 1,850.60 ± 36.83 for 4oK. The outdoor gamma radiation absorbed dose rate in air due to each of the primordial radionuclides was calculated from the mean values of the activity concentration in each sample. The estimated annual outdoor effective dose equivalent for the urban areas in the state .is 50.25 u Svy' while that of rural area is 108.57 u Svy". Average value for the state is 79.41 IlSvy·I Using the estimated population of 6,617,720 for the year / 20b5, the estimated collective effective dose equivalent for the state is 5.26 x 102man- Svy'. The expected number of people in the state at risk of incurring radiation-induced cancer per year was found to be 100.e. risk G = 2 from the urban areas, and 8 from rural areas).