Emanation and exhalation of radon and thoron gases from soil particles

Samples of soil originating from the weathering of granite rock were sieved into eight classes of particle size. Each sieved sample was measured for its content of 226Ra (parent nuclide of radon), 224Ra (parent nuclide of thoron), 228Ac (grandparent nuclide of 224Ra), K, Ca, and Fe as well as for the radon and thoron emanation from it. There was a trend for the contents of 226Ra and 224Ra to increase as particle size decreased. On the other hand, the K content showed a different variation with particle size from the variations found for 226Ra and 224Ra. On the basis of the results of the emanation measurements, it was concluded that smaller soil particles make relatively more contribution to radon and thoron exhalations from the ground surface than larger soil particles, but they make absolutely less because of their smaller abundance.