Anomalous fading of thermoluminescence in oligoclase

In a discussion of the thermoluminescence (TL) properties of meteorites Hasan et al. (1986) suggested that anomalous fading is only exhibited by those samples in which the feldspar is in the low-temperature form. They further suggested that the fading proceeded via tunnelling. This study tests the above hypotheses. A low/high-form phase change in oligoclase is induced by high-temperature vacuum annealing and the fading properties of the two forms so-produced compared. The TL decay is also analysed using both the tunnelling model and the localised transition model, recently proposed by Templer (1986). The data indicate that both the low-temperature and the high-temperature forms of the oligoclase samples examined display anomalous fading. The properties of the fading are not consistent with tunnelling. Instead the qualitative features are well explained by the localised transition model. Quantitative agreement is not obtained, however. This is probably due to the use of an unrealistic energy level distribution in the localised transition model calculations. (author)