Regional and local variation of indoor radon and radon source potentials

Document Type


Publication Date



Health and Medical Physics | Physics


The upper midwest has been identified as an area with high potential for elevated indoor radon. In Minnesota (MN), substantial spatial variations have been observed in radon and radon sources on both regional and local scales. Different methods for identifying 'hot spots' were investigated. Maps generated from existing indoor radon screening measurements averaged over a small area (postal zip code area) correlate well with the average indoor radon concentrations in both high radon and low radon regions within the state. However, a statewide indoor radon map generated from zip code aggregated measurements misses the smaller local hot spots. An intensive study of the spatial variation in Olmsted County, MN, revealed several hot spots within zip code areas. Since many rural regions are poorly represented in indoor radon databases, the usefulness of surrogate measurements, such as the soil radium content, was studied to extend the indoor radon predictions to areas not covered by direct indoor results. Most of the surrogates, including many of those that have been reported as being successful guides in other regions, failed in this region. However, surface 214Bi concentration proved to be a useful, qualitative guide to regional hot spots while radon source potential proved to be a useful, qualitative guide to local hot spots.