2022 年 11 巻 1 号 p. 16-20
In Yomitan-son, a village of Okinawa prefecture located in the subtropical region of Japan, the highest annual average of indoor radon (222Rn) concentration, 220 Bq m-3, has been observed in a private residence by a nationwide survey. In this study, to estimate the distribution and origin of the high concentration, measurements for atmospheric radon were conducted on eight dwellings intermittently from 2005 to 2013. And in situ measurements of gamma radiation energy spectrum on the outdoor ground were performed at 26 points in 2018 to estimate the origin of the high indoor radon concentration. As the result, the highest indoor radon concentration, 289 Bq m-3, was observed in a dwelling. For the seasonal variation, indoor radon concentration in winter is obviously higher than that in summer was observed in several dwellings. From the results for the analyses of gamma radiation data, useful information about the origin of the high indoor radon concentration was not provided in this study.