Luminescence sensitivity changes in quartz

In the luminescence dating of sedimentary or heated quartz, some heat treatment is usually applied to the sample immediately prior to the measurement of the optically stimulated luminescence. In this paper we report experiments on a 30,000-year-old sedimentary quartz, in which we use the luminescence response to a test dose to monitor the changes in sensitivity that are caused by holding the quartz at temperatures from 160 to 280 degrees C for times from 10 s to 22 h. For an optically bleached sample, the monitoring is by both optically stimulated luminescence and the 110 degrees C TL peak; both luminescence signals are shown to have the same sensitisation (i.e. activation energy) characteristics. For natural or laboratory irradiated samples only the 110 degrees C TL peak can be used; sensitivity increases of up to a factor of 1.3 and 3 are observed for the natural and laboratory irradiated aliquots, respectively. Up to four exponential components are used to deconvolve the sensitivity change data; the dominant component has a lifetime at 20 degrees C of about 40 ka. It is concluded that the luminescence centres in this sample have been significantly sensitised while the quartz was buried for about 30 ka. This process must be taken into account when selecting an appropriate preheat procedure for dating. (C) 1999 Elsevier Science Ltd. All rights reserved.