For the public, indoor radon is the main source of exposure from ioniz
ing radiation. Radon gas originates from the radioactive decay chain o
f uranium deposited in rocks or in building materials. In the reviews
mostly a rather steady radon exhalation has been assumed. In a village
of North-East Hungary, however, high radon concentrations have been m
easured, differing strongly in neighbouring houses and varying in time
, due to the interplay of several geochemical phenomena.