Estimation of annual effective dose due to radon and thoron concentrations in mud dwellings of Mrima Hill, Kenya.

This study presents radon and thoron concentration measurements and the corresponding effective dose rates in mud dwellings located in the high background radiation area of Mrima Hill, Kenya. Discriminative technique was used for simultaneous measurement of radon and thoron. The effective dose was evaluated based on the concentration of the isotopes and the time spent indoors. Radon concentration ranged from 16 to 56 Bq m(-3) with an average of 35±14 Bq m(-3) and a corresponding annual effective dose of 0.67 mSv y(-1), while that of thoron ranged from 132 to 1295 Bq m(-3) with an average of 652±397 Bq m(-3) and an effective dose of 13.7 mSv y(-1).