|
71. Second Nationwide Indoor Radon Survey in Japan
Kenzo Fujimoto, Masahiro Doi, and Shinji Tokonami
Keywords: surveys, radon, indoor
The second nationwide indoor radon survey was carried out in Japan during 1993-1996 with radon-thoron discriminative passive radon detectors after the first survey during 1985-91 with the passive radon detectors developed in Karlsruhe Nuclear Research Center since the first survey was suspected to overestimate the average indoor radon concentrations due to the thoron contribution to the detector. Twenty houses were selected in each prefecture in Japan for the survey. A total of 940 houses were measured. However, the total available data were reduced to 899 houses (Fig. 22) after scrutinizing the data to find out improper handling of the measurements. The radon monitor was installed in a bedroom or living room in each house for successive four three-month periods. The annual mean indoor radon concentration was estimated from the four measurements in each house. The mean, median and geometric mean of indoor radon concentration in Japan were obtained to be 15.5, 11.7 and 12.7 Bq m-3, respectively, which were about 5 Bq m-3 lower than the results obtained by the first nationwide indoor radon survey. In the second survey the data were used only for the estimation of average concentration in Japan and each region but not for each prefecture since sampling number for each prefecture was less than 20. The radon concentration shows approximately a log-normal distribution. Seasonal variation of the radon concentration was found that the radon concentration was high in the fourth quarter (from October to December) and low in summer (from July to September). Variability among house structure types was also found that wooden houses have lower radon concentration than concrete or concrete block houses. The effective dose to the general public due to radon and its progeny was estimated to be 0.44 mSv y-1 in Japan using the same assumption given in the UNSCEAR 1993 report.
Publications:
1) Fujimoto K. et al.: NIRS-R-32, 1997.
2) Fujimoto K. et al.: NIRS-R-34, 1998.
3) Sanada T., Fujimoto K., Miyano K., Doi M., Tokonami S., Uesugi M. and Takata Y.: Env. Radioactivity , 45, 129-137, 1999.
