THE STUDY OF THORON AND RADON PROGENY CONCENTRATIONS IN DWELLINGS IN JAPAN

This paper aims to make a comparison of different concentrations of thoron (Rn-222) progeny and radon (Rn-222) progeny in different kinds of dwellings. The Potential alpha energy concentrations and the effective dose equivalent caused by thoron and radon progeny, respectively, have also been estimated. The measurements were carried out in 23 dwellings. The results indicate that thoron progeny concentrations indoors might be strongly affected by the type of building material used. Traditional Japanese buildings made with mud may have high thoron progeny concentrations of about 3.52 Bq.m-3 and a concentration ratio of thoron progeny to radon progeny of about 0.5, whereas in concrete dwellings thoron progeny concentrations are about 0.72 Bq.m-3 and the concentration ratio of thoron progeny to radon progeny is about 0.1. The annual effective dose equivalent of thoron progeny is 1.23 mSv in mud dwellings and 0.25 mSv in concrete dwellings.