Abstract
The effect of thermal excitation on paramagnetic defects in natural sedimentary quartz irradiated with different doses of gamma radiation was studied using electron spin resonance (ESR) spectroscopy. We report a variation in the activation energy and the frequency factor for [AlO4/h+]0 and [TiO4/M+]0 paramagnetic defects with the gamma dose, for a dose range investigated between ∼100 Gy and ∼40 000 Gy. Our results indicate that both [AlO4/h+]0 and [TiO4/M+]0 defects are less thermally stable above 1 kGy–2 kGy than below this dose range. The correlation between the two kinetic parameters (activation energy and frequency factor) satisfies the Meyer–Neldel rule. A linear correlation was found between the amplitude of the ESR signals of [AlO4/h+]0 and [TiO4/M+]0 paramagnetic defects corresponding to different doses after the application of thermal treatments in the pulse annealing procedure. We propose a mechanism involving the exchange of the cation, assigned mainly to Li+ here, between the two defects. Under irradiation, the cation is removed from [AlO4/M+]0 (forming [AlO4/h+]0) to [TiO4]− (forming [TiO4/M+]0), while under heating, the reverse mechanism takes place. The migration energy of the cation from one defect to another was found to be about 51 meV, corresponding to a temperature of about 325 °C.
Highlights
Signals from [AlO4/h+]0 and [TiO4/M+]0 paramagnetic centers are generally used to date sedimentary quartz by electron spin resonance (ESR) because of their easy identification and quantification as well as their response to irradiation (Toyoda and Ikeya, 1991a; Rink et al, 2007; and Tissoux et al, 2008)
A comprehensive understanding of the thermal decay kinetics of these defects is of utmost importance for dating and for thermochronometry (Grün et al, 1999; King et al, 2020), the majority of studies carried so far circumvented the time-consuming determination of laboratory kinetics by adherence to the standard literature values or performed investigations only for a single laboratory given dose under the assumption that the decay parameters do not depend on the given dose
A higher density of defects clearly exists, and very recent studies on irradiated ionic solids such as Al2O3, MgO, and MgF2 showed that the defect recombination kinetics is not characterized uniquely by the activation energy with a constant preexponent, but, instead, these parameters depend on the radiation dose (Kotomin et al, 2018; Popov et al, 2018; and Baubekova et al, 2020)
Summary
Signals from [AlO4/h+]0 and [TiO4/M+]0 paramagnetic centers are generally used to date sedimentary quartz by electron spin resonance (ESR) because of their easy identification and quantification as well as their response to irradiation (Toyoda and Ikeya, 1991a; Rink et al, 2007; and Tissoux et al, 2008). Another prerequisite for accurate dating is the use of a thermally stable signal. No studies have so far investigated such a possible effect in quartz
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