Radon measurements in Finnish houses

Bare nuclear track detectors were used to study the geographical distribution and temporal variation of radon in indoor air. Measurements were made in 2154 houses in 108 localities. All houses were one family or terrace houses (small houses). On the basis of the local medians the country was divided into four zones, in which the distribution of radon in houses was treated separately. The zonal distributions were combined to a national distribution for small houses. The weather conditions have a strong effect on radon levels in houses. The use of radon rich water is very seldom the major source and cannot explain the highest concentrations. The concentration medians correlate with the external dose rate and radium concentration of the local soil. The highest concentrations in all parts of the country were measured in houses on eskers and rocks. Differences in radon exposure are not reflected in the present geographical distribution of the incidence of lung cancer in Finland. (author)