Measurements of 220Rn emanation from rocks.

Abstract

Alpha-particle and gamma-ray measurements are employed to determine the individual emanation and production rates associated with the thorium radioactive series for thirty-seven rock specimens of approximately 200 cm3 individual volume representing igneous, sedimentary, and metamorphic types. These results are combined to establish 220Rn emanating powers for each of these specimens, and a wide range of values is observed. The generally large 220Rn emanation observed for these specimens strongly indicates that non-tortuous diffusion paths are commonly present in the associated structures, which gives more evidence for the existence of well-connected pore networks at the nanometer level in many of the specimens studied. While the results are qualitatively explainable, they are not predictable in terms of the current macroscopic observables. Since 220Rn and 222Rn emanation rates from rock specimens have previously been found to be comparable in magnitude, the relatively fast determination of 220Rn emanation rates described herein (measurements involving 1-h duration) is in reasonable probability indicative of a comparable 222Rn emanation rate: The employment of 220Rn as a convenient screening tool for potentially high 222Rn emanation sources is indicated.