Kaolinite as an in situ dosimeter for past radionuclide migration at the Earth's surface |
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| Institution: | 1. Laboratoire de Minéralogie-Cristallographie, Universités Paris 6 et 7, UMR CNRS 7590 et IPGP, 4 Place Jussieu, 75252 Paris Cedex 05, France;1. Leibniz Institute of Surface Modification, Permoserstr. 15, 04303 Leipzig, Germany;2. Department of Chemistry, Faculty of Science, Al-Azhar University, Nasr City, 11884, Cairo, Egypt;3. Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry, Faculty of Chemistry and Mineralogy, University of Leipzig, Permoserstr. 15, 04318 Leipzig, Germany;1. Bozok University, Department of Geological Engineering, 66100, Atatürk Way, Yozgat, Turkey;2. Ankara University, Department of Geological Engineering, 06100, Tandogan, Ankara, Turkey;1. Department of Ecology and Natural Resources Management, Norwegian University of Life Sciences, P. O. Box 5003, NO-1432 Ås, Norway;2. Department of Land Resource Management and Environmental Protection (LaRMEP), Mekelle University, Ethiopia;3. UNESCO, Paris, France;1. Faculty of Chemistry, Adam Mickiewicz University, 89b Umultowska Str., 61-614 Poznan, Poland;2. Adam Mickiewicz University Center for Advanced Technologies, 89c Umultowska Str., 61-614 Poznan, Poland;1. Japan Atomic Energy Agency, Sector of Fast Reactor and Advanced Reactor Resaerch and Development, 4002 Narita-cho, Oarai, Ibaraki, 311-1393, Japan;2. Tokyo City University, 1-28-1 Tamazutsumi, Setagaya, Tokyo, 158-8557, Japan;3. Japan Atomic Energy Agency, Sector of Fast Reactor and Advanced Reactor Resaerch and Development, 65-20 Kizaki, Tsuruga, Fukui, 914-8585, Japan;4. Inspection Development Company Ltd., 4002 Narita-cho, Oarai, Ibaraki, 311-1393, Japan |
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| Abstract: | The origin of 3 types of point defects (A-, A′- and B-centers) in kaolinite, due to natural irradiation and detected by electron paramagnetic resonance spectroscopy (EPR), has been demonstrated by artificial irradiation. The potential use of tracing the dynamics of the transfer of radionuclides through A-centers (i.e. the most stable centers) was qualitatively tested on different low-temperature alteration systems, some associated with U-concentrations. This paper proposes a quantitative approach to the reconstruction of the past migration of radionuclides by dosimetry of A-centers. With this aim in mind, the efficiency of α- and γ-radiations to produce A-centers was determined by experimental irradiation. Parameters extracted from A-center growth curves, together with their relationship with a parameter describing the degree of order of kaolinite, permitted (i) a definition to be made of the dose range in which a given kaolinite could be used as a dosimeter and (ii) the quantitative derivation of U-concentration from the cumulative dose (paleodose) of kaolinites. This was achieved by a formalism that accounted for the contribution of natural radiosources to the production of A-centers. The formalism was applied to the Nopal I U-deposit (Chihuhua, Mexico), considered as a natural analogue of a high level nuclear waste repository. Irrespective of the scenario considered, in terms of kaolinite age and of degree of isotopic disequilibrium in the system, A-center dosimetry permitted the determination of past occurrences of U which were several orders of magnitude higher than the present-day measured U-concentrations. Furthermore, this approach also provided evidence for several previous episodes of U-migration. EPR spectroscopy is thus a unique tool for the quantitative, indirect assessment of past radionuclide migration in the geosphere and kaolinite is a reliable in-situ dosimeter. |
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