Measurement of activity concentrations of rock samples from rocks- surrounded town in Igbeti, Oyo State, Nigeria

Abstract

Rocks are known to contain radionuclides that emit radiation continuously. The assessment of activity concentrations of rock samples from Igbeti, Oke-Ogun has been investigated. Twenty (20) rock samples were randomly collected from different rock sites. The rock samples were pulverized at the laboratory of the Department of Geology, University of Ibadan. 200g of each collected sample was allowed to attain secular equilibrium by enclosing it in a plastic container for twenty-eight (28) days. Radiometric analysis of the samples was carried out at the radiation laboratory of the Physics Department of the Federal University of Agriculture, Abeokuta using a thallium doped Sodium Iodide detector. Standard equations were used to estimate the radiological parameters associated with exposure to ionizing radiation from the natural radionuclides in the rock samples. The study revealed that the activity concentrations of 226Ra, 232Th, and 40K lie between 14 ̶ 487 (Bq/kg), 210 ̶ 3680 (Bq/kg), and 242 ̶ 1580 (Bq/kg) respectively. The absorbed dose rate (nGy/h), annual effective dose equivalent (μSv/y), (radium equivalent (Bq/kg), external and internal indices, activity utilization index and estimated excess lifetime cancer risks lie between from (180 ̶ 2700) nGy/h, (0.10 ̶ 14), 400 ̶ 6300 (Bq/kg), 1 ̶ 17, 1 ̶ 19, 2 ̶ 41, and 0.6 ̶ 9.5 × 10−6 respectively. The values of the absorbed dose rates value are greater than the world average of 60 nGy/h while annual effective dose equivalent values are less than the world’s average value of 1000 μSv/y respectively. The external and internal indices are greater than the permissible limit of (1) and likewise, the radium equivalent value is also greater than the acceptable limit of 370 Bq/kg. The estimated excess lifetime cancer risk for the study is below the permissible limit of 2.9 × 10−4 . Most of the estimated radiological parameters for the study are all greater than the permissible limit. This suggests that further exposure of dwellers to ionizing radiation may be possible and this calls for further investigation.