Radon-222 emanation characteristics of rocks and minerals

The activity, emanation rate and percentage of radon-222 escape were investigated for a variety of rocks and minerals using alpha scintillation counting techniques. Rocks show a wide range of leakage with values ranging from 1 to 20% and an activity of 2 to 80 x 10-4pCi/h.g under identical laboratory conditions. The stronger emanations were found among granitic rocks and conglomerates whereas basic and calcareous rocks showed the lowest values. Accessory minerals, although rich in uranium, show very low radon emanation, i.e. less than 1 to 2%. The lack of dependence of emanation on parent uranium concentrations was clearly established. Also a positive correlation was observed between weathering and radon escape and between natural alpha dose and emanation. High-temperature experiments (up to 1200degC) on minerals demonstrated a progressive decrease in the percentage of radon loss. This phenomenon appears to be the result of annealing of natural radiation damage. As expected, an increasing radon loss with decreasing particle size was observed. The temperature dependence of radon emanation in the range of -80degC to +250degC was investigated and showed a strong adsorption for temperature below -20degC. (author)