SURVEY OF RN-222 CONCENTRATIONS IN DWELLINGS AND SOILS IN THE DUTCH BELGIAN BORDER REGION

Rn-222 levels in dwellings and soil gas have been investigated in the Eijsden-Vise region, located at the Dutch-Belgian border, in order to analyze the relationship between domestic radon levels and soil gas ra don levels, in view of the fact that the local geology varies substant ially from uranium-rich to uranium-poor rocks and soils. During Februa ry 1992, charcoal detectors were exposed for 24 h in 116 dwellings in the township of Vise, a radon prone area in Belgium. As expected, the results show a large regional variation, with an averaged indoor air r adon level of 116 Bq m(-3). In the nearby township of Eijsden, the Net herlands, an area with a lower radiation level, similar measurements b y means of charcoal detectors in 42 dwellings during March 1993, resul ted in an averaged indoor Rn-222 concentration of 46 Bq m(-3). Further more, in the same region time-integrated radon measurements were perfo rmed in 15 dwellings on different floors. These results indicate that a gradient in indoor air radon concentration exists from basement to u pper floor level. In addition, a significant positive correlation has been found between radon gas levels of soils surrounding 26 houses and indoor air radon levels. The variation in indoor air radon levels in the region under study is mainly due to the variation of the radon lev els in the soils. A soil gas radon survey is suitable for prescreening of the radon potential of an area taking into account the spatial het erogeneity of the local geology.