Surveys of concentration of radon isotopes in indoor and outdoor air in Japan

Abstract

A series of radon and 220Rn surveys using passive radon 220- Rn discriminative dosimeters were conducted in the Masutomi radium spa region, Yamanashi Prefecture, and at several subway stations in Metropolitan Tokyo. In Masutomi, the highest outdoor radon concentration was 569.8 ± 59.5 (SE) Bq m −3 and the lowest, 7.4 ± 0.1 (SE) Bq m −3, while the highest outdoor 220 Rn concentration was 142.8 ± 52.7 (SE) Bq m −3 at 0.04 m above the ground. The outdoor 220Rn concentrations at some survey sites increased as the ground surface approached. The highest radon and 220Rn concentrations in the public bathhouse were 530.2 ± 74.4 (SD) Bq m −3 and 592.0 ± 226.8 (SD) Bq m −3, respectively. Average indoor radon concentrations in the two houses in Masutomi, were 35.9 ± 2.9 (SE) Bq m −3 and 14.2 ± 1.4 (SE) Bq m −3, respectively. Indoor and outdoor radon and 220Rn concentrations within a square kilometer region in Masutomi showed the irregular distributions, which might be easily influenced by the local geology and meteorology at each survey site. Average radon concentrations at several subway stations in Metropolitan Tokyo were 10.9 ± 1.1 (SE) Bq m −3, which was unexpected. Significant 220Rn concentrations were not observed at all survey sites (except some platforms, where values ranged from 11–12 Bq m −3) since the ventilation system of all subway stations exchanged the stale air with the fresh air above ground entirely.