Abstract The aim of this study was to evaluate the level of natural radioactivity concentrations of 238U, 232Th and 40K in the surface (0-5cm) soil samples collected from Odigbo in the Southwestern region of Nigeria. The surface soils were collected along the streets of this city. The activity concentrations of naturally-occurring radioactive materials in the 238U, 232Th and 40K were determined by means of a Sodium Iodide (NaI) gamma-ray spectrometry system detector in a low background configuration. The mean activity concentrations of 238U, 232Th and 40K for Odigbo were found to be 179.07±11.36, 152.32 ±32.71 and 1617.43±9.90 Bq kg-1. The results of this current study have been compared with the world mean values of 37, 33 and 400 Bq kg-1, respectively specified by the United Nations Scientific Committee on the Effects of Atomic Radiation. The average annual effective dose obtained from this study is 0.22 mSv y-1 for Odigbo, which is still less than the recommended limit of 1 mSv y-1 by International Commission on Radiation Protection [ICRP] for non occupational population. Also the mean radium equivalent for Odigbo is 535.56 Bq kg-1 and its absorbed dose is 175.21 nGy h-1. It was shown that in most of the locations studied 40K has the highest concentration.
Keywords Annual effective dose, radium equivalent and absorbed dose.