Radiation-induced defects in quartz. IV. Thermal properties and implications |
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Authors: | Yuanming Pan Baoqun Hu |
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Institution: | (1) Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK, S7N 5E2, Canada |
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Abstract: | The thermal stabilities and decay kinetics of three peroxy radicals (Centers #1, B and B′) and three other radiation-induced
defects (#3, C′ and E1′) in natural quartz from the high-grade McArthur River uranium deposit (Athabasca basin, Canada) have been investigated by
isochronal and isothermal annealing experiments and electron paramagnetic resonance (EPR) spectroscopy. Single-crystal EPR
spectra of isochronally (2 h) annealed quartz show that these centers all grow in intensity to 280°C and then decay with further
increase in temperature, but their disappearance temperatures differ markedly and depend on the initial concentrations (e.g.,
Center #1 in a dark smoky quartz is annealed out at 380°C, B and B′ at 420°C and #3 and C′ at 580°C). The isothermal decay
processes of these centers are all of the second order type. The calculated activation energies for the peroxy radicals #1
and B + B′ at 0.36 (9) and 0.83 (8) eV, respectively] are smaller than those of Centers #3, C′ and E1′ 1.09 (8), 1.24 (8) and 1.45 (7) eV, respectively]. Gamma-ray irradiations of thermally bleached quartz restore a fraction
of the peroxy radicals, suggesting that their diamagnetic precursors are stable up to at least 800°C. The unusual decay characteristics
of “peroxy radicals” in quartz reported in the literature are shown to most likely arise from multiple radiation-induced defects.
These results have implications for not only applications of peroxy radicals in quartz for EPR dating but also better understanding
of thermoluminescence and cathodoluminescence spectra of this mineral. |
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Keywords: | Peroxy radicals Natural quartz Single-crystal EPR Thermal stability Decay kinetics EPR dating Thermoluminescence Cathodoluminescene |
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