Quartz thermoluminescence spectra in the high-dose range
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The red thermoluminescence (RTL) emission of quartz is associated with advantageous features such as high saturation dose and good reproducibility. Previous studies, however, noted inexplicable RTL glow curve shapes with new peaks at large doses (kGy range). Here we present TL spectra of two granitic quartz samples over the additive γ-dose range 0.1–47.9 kGy. While for doses between 0.4 and 1 kGy the TL spectra are dominated by the red emission at 1.95 eV (630 nm), a blue emission at 2.67 eV (465 nm) becomes prominent for higher doses. For one sample, this blue component completely dominates the spectrum for doses > 12.2 kGy with intensity maxima around 200 °C and > 350 °C (heating rate 2 K s−1). The other sample still contains well resolvable red and blue emissions at the largest dose with similar TL peak positions. Signal saturation for the blue emission in the glow curve range 260–300 °C is not yet reached following an additive γ-dose of 47.9 kGy, whereas the red emission generally shows a more subdued signal response for doses > 5–12 kGy. These findings agree qualitatively with additional monochromatic blue and red TL measurements on the same samples. The evolution of supplementary radiofluorescence spectra over the entire γ-dose range is more complex, but suggests that the sensitisation of the blue wavelength region occurs during heating and not during irradiation and through creation of electron traps rather than recombination centres (most likely [AlO4]0 sites). The sharp sensitivity increase at 1 kGy might likewise be related to alkali ion redistribution and/or the removal of non-radiative competitive recombination pathways. While the blue emission still requires thorough investigation, care should be taken when recording RTL using optical filters since significant portions of the registered TL could originate from the blue component entering the RTL transmission window. In practical terms, the dose-dependent change in relative intensities of blue and red TL emissions might help in detecting exposure to high doses.
KeywordsLuminescence Radiofluorescence Red thermoluminescence Gamma-dose Sensitivity change Recombination centre
We acknowledge support of the Oberfrankenstiftung (Projekt “Niedrigst-Temperatur-Thermochronometrie mittels Thermolumineszenz (Thermalbohrung Weißenstadt)”) and thank Johannes Friedrich for technical assistance. Part of this work was supported by a postdoc fellowship of the German Academic Exchange Service (DAAD, ID 57360695). We thank the two anonymous reviewers for their helpful comments.
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