The Radon Emanation Coefficient: an Important Tool for Geologic Radon Potential

The fraction of radon atoms generated from radium decay that are released from into a rock or soil pore space is defined as the radon emanation coefficient, or emanating power, of the material. The emanation coefficient of rocks and soils typically varies between about 0.05 and 0.70, and an average value for soils is probably between 0.20 and 0.30. Geologic, pedologic, and climatic factors, including radium content, grain size, siting of radon parents within soil grains or on grain coatings, and soil moisture conditions, determine the soil's emanating power and radon transport characteristics. Soils derived from similar parent rocks in different regions appear to have significantly different emanation coefficients due to the effects of climate on these soil characteristics. Data on soil radium content, permeability, and moisture content arc available for many areas of the United Stales. With these and data on emanation coefficients, quantitative predictive models for radon generation in rocks and soils at regional to national scales can feasibly be developed. To predict radon generation from soils at a town, neighboorhood, or building-site scale, however, would require data at a greater level of detail than currently exists.