Results from the Danish Indoor Radiation Survey

A survey of indoor radiation in Danish dwellings has been carried out by measuring the radon concentration and the absorbed dose rate from external radiation in 500 randomly selected dwellings. The measurements were initiated in April 1985 and finalised in March 1986. The radon concentration was measured in the living-room and in a bedroom over a period of six months by means of nuclear track detectors (CR-39). The absorbed dose rate from external radiation was determined in the living-room by means of thermoluminescence dosemeters (LiF). A representative distribution of the annual average radon concentration of the Danish housing stock has been established from the results. The mean radon concentration in Danish dwellings was found to be 47 Bq · m-3 and the population-averaged mean value was 53 Bq · m-3. The highest value of the annual average radon concentration did not exceed 600 Bq · m-3. The mean value of the absorbed dose rate from external radiation in Danish dwellings was found to be 85 nGy · h-1. In terms of average annual effective dose equivalents to the Danish population the survey gives a result of 1.8 mSv · y-1 from radon daughter exposure and 0.32 mSv · y-1 from gamma exposure exclusive of cosmic radiation.