TOWARDS THE DEVELOPMENT OF A PREHEAT PROCEDURE FOR OSL DATING OF QUARTZ

Isothermal decay data for the natural optically stimulated luminescenc e (OSL) of a quartz sample from the Kimberley region of Western Austra lia are presented. These show that >99% of the initial OSL signal meas ured using a broad-band blue/green-light stimulation source is derived from a single trap. A lifetime at 20 degrees C of about 850 Ma is pre dicted for this OSL trap. Since these measurements may be affected by charge transfer or sensitivity changes, both of which are thought to o ccur as a result of heating, the effects of prior heating (preheating) on the shape of the quartz OSL decay curve have been investigated. Th e relationship between the initial OSL (first 0.4 s), the OSL at the e nd of a 100 s stimulation period, and the integrated OSL (0-100 s), is presented at a constant stimulation temperature of 125 degrees C, but following preheats at temperatures between 110 degrees C and 380 degr ees C. It is deduced that both the natural and regenerated OSL are dom inated by a single trap/luminescence centre combination for preheats u p to above 300 degrees C. There is probably a small contribution [abou t 1% of the natural OSL integral (0-100 s) without preheating] from tr aps which are not emptied by heating to 340 degrees C, and which have a longer lifetime. Based on the observation that the initial OSL signa l from 0.1 s stimulation correlates well with the net integral OSL (0- 100 s), the effect of preheat on the natural and regenerated OSL is ex amined again using single aliquots. These curves are then corrected fo r changes in luminescence efficiency with preheating obtained using th e 110 degrees C thermoluminescence from a 0.1 Gy test dose, before fit ting with a simple two trap model. We draw conclusions regarding the i mplications of this study for dating. (C) 1998 Elsevier Science Ltd. A ll rights reserved.