Simultaneous indoor radon/thoron and in situ outdoor gamma dose measurements and estimation of annual effective dose in a tin mining area of Jos Plateau, Nigeria.

Radon, a radioactive gas can increase the risk of lung cancer when breathe in. Indoor Rn-222 and Rn-220 concentrations were determined using passive radon monitor in some dwellings in a Sn mining area of Jos Plateau. Outdoor gamma radiation was also measured with a hand-held survey meter. The range of Rn-222 and Rn-220 concentrations was from 7-53 Bq m-3 to 41-267 Bq m-3 with averages of 27 ± 17 and 92 ± 65 Bq m-3, respectively. The mean total effective dose due to Rn-222 + Rn-220 was estimated as 2.84 ± 1.57 mSv y-1. Rn-220 contributed between 50 and 95% to the total annual effective dose. There was no correlation between indoor Rn-220 and Rn-222 concentrations in the dwellings. Outdoor gamma radiation measured was between 0.31 ± 0.06 and 0.62 ± 0.08 μSv h-1, and mean annual effective dose calculated was 1.14 ± 0.21 mSv y-1. It is concluded from this study that thoron should not be neglected in dose assessment.