Measurements of Thoron Concentration by Passive Cup Method and Its Application to Dose Assessment
A new type of passive integrating cup monitors was developed by using a 50mm radius stainless steel hemisphere to measured indoor radon (<SUP>222</SUP>Rn) and thoron (<SUP>220</SUP>Rn) concentrations. By placing a pair of cup monitors with an air exchange opening of diameter 5mm and four openings of diameter 20mm at a 20cm distance from wall during about three months, the con- centrations of both gases could be assessed from the α track densities on the cellulose nitrate (CN) films. The <SUP>222</SUP>Rn and <SUP>220</SUP>Rn concentrations were surveyed with the cup monitors in the different types of dwellings around Nagoya in Japan over three years. The <SUP>220</SUP>Rn concentrations were rather high in the dwellings with soil wall, and the mean <SUP>220</SUP>Rn concentration was 160±12 Bq•m<SUP>-3</SUP>. The <SUP>220</SUP>Rn exhalation rate from wall and the <SUP>220</SUP>Rn diffusion were evaluated from the distribution of <SUP>220</SUP>Rn concentrations in the dwellings. The results of the surveys have also clarified the relationship between the <SUP>220</SUP>Rn concentrations at a 20cm distance from wall and the <SUP>220</SUP>Rn progeny concentrations measured in the same dwellings. Then, the annual mean effective dose equivalent due to <SUP>220</SUP>Rn progeny was expected to be 0.67mSv•yr<SUP>-1</SUP> in the dwellings with soil wall.
- Journal of nuclear science and technology
Journal of nuclear science and technology 32(8), 794-803, 1995-08-25
Atomic Energy Society of Japan