Activation energies from blue- and red-thermoluminescence (TL) of quartz grains and mean lives of trapped electrons related to natural red-TL

Abstract

A three-dimensional expression of thermoluminescence (TL) spectra has been established by employing an image intensifier unit combined with a simple spectrophotometer and a microcomputer. From this TL spectrometric system, it could be readily recognized that natural quartz grains are distinguished into blue- and/or red-TL ones. In these blue- and red-TL wavelength regions, activation energies from artificially irradiated quartz grains are evaluated using a repeated initial rise method. Apparent difference of activation energies in two different colorations was observed for dune sands presumably originating from different quartz sources. On the other hand, the quartz grains extracted from a volcanic ash sediment showed completely similar activation energies in both TL color regions over all temperatures. Subsequently, the naturally occurring red-TL, possessing an apparent single peak around 340°C, from volcanically originating quartz grains was also analyzed from aspects of kinetic parameters by means of a best fitting procedure of a theoretical equation to glow curves, after evaluating activation energies. On the basis of empirical kinetic parameters, the mean life of trapped electrons relating to a main 340°C peak has proved to possess an efficiently long-life period extended to 1 million years, together with the confirmation of a secondary weak peak around 280°C in the natural red-TL glow curve.