Abstract
Thirty-two samples of concrete building blocks were collected from different block making industries in Ibadan. The radioactivity concentrations of the natural radionuclides in the samples were determined by gamma-ray spectrometry with a NaI(Tl) detector. The radioactivity concentrations varied from 6.2 to 57.5 Bq kg −1, 12.4 to 64.9 Bq kg −1 and 95.3 to 766.1 Bq kg −1 for 226Ra, 232Th and 40K, respectively. The radium equivalent activities of the 32 samples varied from 51.3 to 175.7 Bq kg −1. Radiation exposure levels in 30 dwellings were determined using LiF thermoluminescent dosimeters. The annual equivalent dose rates varied from 0.318 to 0.657 mSv y −1 with a mean of 0.433 mSv y −1. The annual effective dose rate to the whole body was calculated as 0.236 mSv y −1, which is less than that (mean) estimated by UNSCEAR for normal background areas.
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