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.