Isothermal decay of optically stimulated luminescence in quartz

Isothermal decay curves are presented for the optically stimulated luminescence from an Australian sedimentary quartz, measured for 0.1 s at 125 degrees C, using a broad band 420-550 nm light source (similar to 26 mW cm(-2)). Natural and laboratory irradiated samples were held at 160, 180,200, 220, 240, 260 and 280 degrees C for up to 22 h. Laboratory irradiated samples showed a marked increase in OSL prior to the decrease expected as a result of thermal detrapping of charge. This increase was caused by thermally induced sensitivity changes, which were monitored using the response to a test dose of the 110 degrees C TL peak after each OSL measurement. After dividing the OSL data by this TL response to remove the effects of these sensitivity changes, the corrected OSL decay curves showed that, in this sample, the natural signal was dominated by a single decay component, whereas those from laboratory irradiated sub-samples were dominated by two clearly separate components. Kinetic analysis suggests that the less thermally stable signal has a half-life of < 1000 yr at 20 degrees C, and would be removed by the preheats commonly used in dating applications. The more stable signal, present in both the natural and laboratory irradiated samples, has a lifetime of about 1 x 10(8) yr at 20 degrees C, confirming its suitability as for dating. (C) 1999 Elsevier Science Ltd. All rights reserved.