Intercomparison of Radon Measurement with Passive Method in Japan

Intercomparison exercises were performed during the period from January 1989 to September 1991 on passive 222Rn measurements at Critical Assembly Building of the Research Reactor Institute, Kyoto University (KUCA) and Nagoya University (NU). Most of the institutions in Japan which practiced passive 222Rn measurements participated in the exercises which were carried out in 4 rounds. Numbers of participating institution were 4, 6, 12 and 13 for the first, second, third and fourth rounds, respectively. The methods entered in the intercomparison was: (1) electrostatic collection method using solid-state nuclear-track detector (SSNTD), thermoluminescent dosimeter (TLD) and photodiode detector as detectors, (2) cup method with SSNTD in a filtered cup, and (3) are method using a bare SSNTD. The round 1 intercomparison of 3-day exposure were performed in a room of KUCA of about 470 Bq·m-3 that was evaluated using a flow-through ionization chamber. The average value for the 4 participating institutions was 430±38Bq·m-3. For the second and third rounds, 222Rn concentrations with the ionization chamber were 56 and 47Bq·m-3 in a preparation room of KUCA. The average concentrations obtained by passive methods for exposures of 39 and 58 days were 56.5±10.3 and 48.6±9.5Bq·m-3 for the second and the third rounds, respectively. Fourth run was made on the campus of NU at outdoor 222Rn concentration of 3-7Bq·m-3 that was measured with an electrostatic 222Rn monitor (ERM). The integrating 222Rn concentrations were 4-10kBq·m-3·h for exposure of two months, 9-14kBq·m-3·h for three months and 18-25kBq·m-3·h for six months. The mean ratio of the measured values with passive monitors to ERM was 1.17±0.41. Results of measurements agreed fairly well with those obtained with active methods, although standard deviations were rather large, especially in cup and bare methods.