Abstract
New dose conversion factors (DCF) for radon progeny inhalation have been presented in the latest ICRP publication 137. There used to be a large difference in the DCF between those derived from epidemiological (ICRP 65) and from dosimetric approaches (ICRP 66). In parallel, UNSCEAR has presented their own DCF. The UNSCEAR DCF fell in the two results given by ICRP. This revision results in a higher DCF than before. This is based on the recently new scientific findings obtained by pooled analyses of epidemiological data from European studies on residential radon and lung cancer. Although the publication 137 is used only for occupational exposures, it will be able to be applied because of the consistency. For occupational exposures the new DCF is two times higher than the previous value and is estimated to be 17 nSv per Bq h m-3. It may be different from the previous one by a factor of more than 3 for public exposures (approximately 21 nSv per Bq h m-3). Using the mean indoor radon concentration in Japan, an annual effective dose due to radon progeny inhalation indoors is estimated to be 0.9 mSv a-1. As the DCF is calculated according to aerosol characteristics, site-specific DCFs can be provided.
