Annual effective dose due to natural radionuclides in building blocks in eight cities of Southwestern Nigeria

The specific absorbed dose rates due to Ra-226, Th-232 and K-40 in building blocks have been determined for a model dwelling dimension of 3.6 x 3.6 x 3.0 m(3), wall thickness 10 cm and density of 1.73 x 10(3) kg m(-3) in eight cities across Southwestern Nigeria. The Mustonen method of calculating gamma-ray annual exposure rate from the radioactivity concentrations (Bq kg(-1)) of Ra-126, Th-232 and K-40 in the blocks have been adopted with modifications to suit the Nigerian situation. The specific absorbed dose rates obtained were as follows: 11.36, 14.94 and 0.92 mu Gy y(-1) per Bq kg(-1) for Ra-226, Th-232 and K-40, respectively. These dose rates were used to calculate the annual effective dose in the model dwelling. The annual effective dose obtained varied between 209.20 (Osogbo) and 400.36 mu Sv y(-1) (Abeokuta). The values are in the range of values obtained for the German Democratic Republic (309 mu Sv y(-1)) and Jordan (470 mu Sv y(-1)).