Measurement of activity concentrations of natural radionuclides in the topsoil of IITA Ibadan by gamma-ray spectrometry

摘要

The activity concentrations of the natural radionuclides in the soils at the International Institute of Tropical Agriculture, ( IITA), Idi-Ose, Moniya, Ibadan, Nigeria were investigated using a NaI (Tl) scintillation detector coupled with a Canberra series 10 plus multichannel analyser as the detecting device for gamma scintillation spectroscopy. The whole area was divided into grids and soil samples were collected from the points of intersection of the grids. The average activity concentrations obtained for the three radionuclides (K-40, U-238 and Th-232) were 180.08 +/- 90.54 Bq kg(-1) for K-40, 8.901 +/- 5.063 Bq kg(-1) for U-238 and 11.01 +/- 7.686 Bq kg(-1) for Th-232. The average values of the absorbed dose rate for each radionuclide were found to be 7.33 nGy h(-1) for Th-232, 7.55 nGy h(-1) for K-40 and 3.82 nGy h(-1) for 238U. The average ( baseline) of the total absorbed dose rate was found to be 18.72 +/- 8.11 nGy h(-1). The baseline average outdoor annual effective dose equivalent at IITA due to the concentrations of the radionuclides was found to be 22.95 +/- 9.94 mu Sv y(-1). This value is low compared to the world average of 70 mu Sv y(-1) specified by UNSCEAR for an outdoor effective dose. Hence the probability of occurrence of any of the health effects of radiation is low. ( Some figures in this article are in colour only in the electronic version)