Measurements of Thoron Concentration by Passive Cup Method and Its Application to Dose Assessment

概要

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A new type of passive integrating cup monitors was developed by using a 50mm 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 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 222Rn and 220Rn concentrations were surveyed with the cup monitors in the different types of dwellings around Nagoya in Japan over three years. The 220Rn concentrations were rather high in the dwellings with soil wall, and the mean 220Rn concentration was 160±12 Bq•m-3. The 220Rn exhalation rate from wall and the 220Rn diffusion were evaluated from the distribution of 220Rn concentrations in the dwellings. The results of the surveys have also clarified the relationship between the 220Rn concentrations at a 20cm distance from wall and the 220Rn progeny concentrations measured in the same dwellings. Then, the annual mean effective dose equivalent due to 220Rn progeny was expected to be 0.67mSv•yr-1 in the dwellings with soil wall.
社団法人日本原子力学会の論文
1995-08-25