Preferential leaching and the age of radiation damage from alpha decay in minerals |
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| Authors: | Yehuda Eyal Robert L Fleischer |
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| Institution: | 1. General Electric Research and Development Center, Schenectady, New York 12301 U.S.A.;2. Department of Nuclear Engineering, Technion-lsrael Institute of Technology, Haifa 32000, Israel |
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| Abstract: | Preferential release into solution of radionuclides that result from alpha decay is a contributor to natural isotopic disequilibrium. Such release is critical to geochemical understanding of alpha-decay products and would be an undesirable characteristic of solidified nuclear waste in deep geological formations. Spontaneous annealing of the radiation damage that is responsible for the preferential release is shown to diminish the effect in thorianite and uraninite which we have found to be 550 to 1000 M.y. old, respectively. Leaching experiments and measurements of the thorium and uranium isotopes show that there is strongly enhanced release of short-lived 228Th relative to 232Th, but only slight enhancement of long-lived 234U and 230Th relative to 238U and 232Th. These results are interpreted in terms of natural annealing of damage occurring on a time scale between the ~10 and 105 years of the alpha-decay products. With a simple assumption actual times for the survival of the enhanced leaching in these minerals are ~ 15,000 years. |
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