Rn level in the internal air of residential rooms in Switzerland: Influences of geology, climate and energy conservation measures

In wide parts of the Swiss Alps as compared with the rest of the country, an increased Rn level was measured in the internal air of residential rooms. The marked decline of measured values from the cellar to the ground floor and to the upper floors indicate the dominance of geological factors, i.e. of the subsoil. Measurements carried out in the winter of 82/83 in 32 self-contained houses in the South-East Buenden area showed lognormal distributions of the values with a geometric average of 766 Bq/m3 (20.7 pCi/l) Rn gas in the cellar, 255 Bq/m3 (6.9 pCi/l) on the ground floor, and 177 Bq/m3 (4.8 pCi/l) on the 1st floor. By applying the UNSCEAR82 conversion factors to the arithmetical mean of the residential rooms, the resulting annual radiaton exposure is 9 mSr (900 mrem) effective dose equivalent. The respective dose rates received by the parent cells of the tracheo-bronchial tissue of the lungs are about 100 mSv/a (10 rem/a) of alpha radiation. Besides the content in radium and porosity of the building subsoil, the content in radon of the drinking water must be considered in central Alpes areas. An investigation of drinking water in the Upper Wallis and in the head-stream of the river Rhine showed a lognormal distribution of measured values with a geometric average of 26.5 kBq/m3 (716 pCi/l). The 10% fractile was 118 kBq/m3 (4.3 nCi/l). (orig./HP)