Measurements of radon exhalation from the ground: a usable tool for classification of the radon risk of building ground

In the Nordic countries, very high indoor radon concentrations occur in several areas. Some classification of the radon risk of geological areas may be made by geological knowledge alone, but locally, more investigations must be performed to be able to judge the potential radon risk in future houses. Different geological areas are discussed, and a method for radon exhalation measurements presented. The method is based on a combination of activated charcoal and TLD which makes it possible to carry out large scale surveys at relatively low cost. The method has been used at several sites in Denmark and Norway, and the results of exhalation measurements have been compared with measurements of indoor radon concentrations. Radon exhalation measurements seem to be suitable for local classification of radon risk in most cases. In areas with very high permeability, however, the radon risk may be high even though radon exhalation at the ground surface is low. (author)