220Rn and its progeny in buildings in Sweden

Abstract

Measurements of 220Rn have been performed in some 90 buildings during 1992 and 1993, as parts of two different investigations. In the first study, 220Rn progeny measurements were undertaken in 53 dwellings and 7 workplaces at 13 different locations in south and central Sweden. Most buildings were situated in areas with elevated natural thorium concentrations. The 222Rn progeny concentration was measured at the same time. The thorium and uranium activity concentrations in the rock and soil surrounding the buildings were also measured. Typical 220Rn progeny values (equilibrium equivalent concentration of 220Rn) in the living areas were in the range 0.1 to 1.0 Bq m −3 (8 to 76 nJ m −3, Potential Alpha Energy Concentration (PAEC)) with a mean of 0.9 Bq m −3 (68 nJ m −3). The measurements in the basements had a mean of 1.5 Bq m −3 (114 nJ m −3). A few measurements of 220Rn gas were performed in basements and showed typical values between 10 and 80 Bq m −3, with a maximum of 430 Bq m −3. As part of a study of long-term variations of 222Rn in dwellings located in different parts of Sweden, 24-h continuous measurements of 220Rn gas were performed in 28 of these dwellings. In this study, the buildings were chosen regardless of natural thorium concentrations. The mean of these measurements was 13 Bq m −3. One high value of 150 Bq m −3 was found. The estimated number of dwellings with 220Rn progeny levels exceeding 20 Bq m −3 EET in Sweden is about 200. The estimated population mean for 220Rn progeny in Swedish homes is 0.5 Bq m −3 (38 nJ m −3). This would give an approximate annual effective dose to the average Swede of 0.1 mSv.