Measurements of Thoron and Thoron Progeny Indoors in Sweden

Abstract

In order to assess the risk for high thoron levels indoors, measurements of thoron progeny have been performed in a number of buildings in Sweden. Some of the measurements have been made in detached houses in areas with elevated natural thorium concentrations. The radon progeny concentration was measured at the same time. Up to the summer of 1991 measurements of thoron progeny concentrations have been made in nine dwellings, eight cellars and four workplaces in 12 different buildings. The mean thoron progeny concentration in the measured dwellings was 0.3 Bq.m-3 (EET) and in the cellars 1.5 Bq.m-3 (EET). The highest thoron progeny value measured so far in this investigation in the living space of a dwelling was 0.6 Bq.m-3. In a cellar of a detached house we have measured 3.09 Bq.m-3. The highest values have been found in houses built on an esker in central Sweden with a high natural thorium concentration (120 Bq.kg-1). Elevated radon progeny levels were also found in these houses.