Measurements of thoron concentration by passive cup method and its application to dose assessment

Abstract

A new type of passive integrating cup monitors was developed by using a 50 mm radius stainless steel hemisphere to measured indoor radon (222Rn) and thoron (220Rn) concentrations. By placing a pair of cup monitors with an air exchange opening of diameter 5 mm and four openings of diameter 20 mm at a 20 cm distance from wall during about three months, the concentrations of both gases could be assessed from the a track densities on the cellulose nitrate (CN) films. The222Rn and22l)Rn concentrations were surveyed with the cup monitors in the different types of dwellings around Nagoya in Japan over three years. The222Rn concentrations were rather high in the dwellings with soil wall, and the mean220Rn concentration was 160± 12 Bq-m-3. The220Rn exhalation rate from wall and the220Rn diffusion were evaluated from the distribution of220Rn concentrations in the dwellings. The results of the surveys have also clarified the relationship between the220Rn concentrations at a 20 cm distance from wall and the220Rn progeny concentrations measured in the same dwellings. Then, the annual mean effective dose equivalent due to220Rn progeny was expected to be 0.67 mSv-yr-1 in the dwellings with soil wall. © 1995 Taylor & Francis Group, LLC.