Measurement of Thoron and Its Progeny in Traditional and Modern Earthen Buildings in Germany: Methodology and Results

In the past, the radon isotope Rn (thoron) was often paid little attention in the context of radiation protection at home. Measurements in buildings on the Central-Chinese Loess Plateau have shown, however, that in dwellings built from unfired earthen material, thoron and its progenies can significantly contribute to the inhalation dose of the dwellers. In Germany, such buildings mainly comprise traditional half-timbered houses and modern ecological low-energy houses with clay boards and plaster. Measurements of thoron in several such houses show concentrations of up to 150 Bq/m (at 20 cm distance from the wall). Radon and thoron progenies were measured with a newly constructed device which makes use of aerosol precipitation in an electric field upon solid-state nuclear track detectors. Thoron progeny concentrations were in the range from 100 to 1000 nJ/m resulting in a dose contribution of up to about 4 mSv per year.