Dose due to thoron and its decay products in Chinese loess plateau

Abstract

It is well known that numerous cave dwellings are widely distributed in Chinese loess plateau. In order to prevent an interference by this thoron presence to radon measurements, a simple discriminative passive monitor was newly developed and then was introduced to the survey program of the Chinese loess plateau. As a result, high concentrations of indoor thoron over 200 Bq/m3 were observed. Comparing with such gas concentrations, equilibrium equivalent thoron concentrations, EETC, were found to be not so high. It suggests that equilibrium factor is fairly low, comparing with the conservative expectation in the UNSCEAR 2000 report. Effective doses due to radon and thoron were estimated, respectively. As the contribution of thoron to an effective dose is large, importance of the radon and thoron discriminative measurement is reconfirmed. [J Radiat Res 44:420 (2003)]