The effect of pre-irradiation annealing on TL glow curves of LiF (Mg)

The practice of pre-annealing dosimeter crystals before irradiation is exam ined in this investigation. LiF crystals with high (2000 ppm) and low (100 ppm) concentrations of Mg impurities are investigated using optical absorpt ion (OA), photoluminescence (PL) and thermoluminescence (TL) techniques. Pr e-annealing was at 400 degrees C for 1 in and irradiations were with gamma- rays from an Am-241 source in the dose range 0.6-8.0 kGy. In 2000 ppm sampl es pre-annealing produces noticeable effects at low doses, namely enhanced optical absorption at 310 nm compared with untreated crystals but reduced i ntensity in the glow curves. At higher doses, the glow curves are similar b ut pre-annealed samples have a significantly smaller TL response, Pre-annea ling 100 ppm samples produces smaller changes. Some implications for thermo luminescences are considered. The present results can be explained by consi dering the effects of pre-irradiation annealing on the distribution of Mg w hich acts as a trapping centre for interstitial fluorine atoms. (C) 2000 El sevier Science B.V. All rights reserved.