Defect production by X- and gamma-rays in gamma lithium aluminate

Abstract

Using electron paramagnetic resonance measurements (EPR), we detected paramagnetic defects in γ-LiAlO 2 single crystals irradiated by X- or gamma-rays at room temperature. We studied (i) their production as a function of dose and (ii) their recovery during an isochronal annealing series from room temperature up to 300°C. At low doses (⩽10 6 Gy) an eleven-line signal is observed; in addition, two distinct six-line signals appear at higher doses (⩾ 10 7 Gy). The colour centres originating these EPR signals involve an electron located near two equivalent aluminium nuclei (eleven-line signal) or one aluminium nucleus (six-line signals). Furthermore, as observed by both EPR and optical absorption measurements, there is no trace, in the X-ray- and gamma-ray-irradiated samples, of the major defect that we detected previously in electron-irradiated samples [M.H. Auvray-Gely, A. Perez and A. Dunlop, to appear in Philos. Mag.]. This defect—that could be an F +-centre—is therefore not created through a radiolysis mechanism.