Temperature distribution in thermoluminescence experiments. Pt. 1

In a typical thermoluminescence experiment, a sample rests on a metallic strip which is heated in a controlled fashion so that the strip temperature rises linearly with time. Thermal contact is improved by the use of an inert exchange gas, usually argon. With this procedure, samples of interest emit light spectra of low intensity as electrons escape from traps. The technique is applied, for example, to dating of artefacts or geological materials, to radioactive dosimetry, and to the characterization of optical materials. In this paper we present data which show that it is unsafe to make the common assumption that, during ramping, the light-emitting parts of the sample have the same temperature as the heating strip. We have performed experiments designed to demonstrate sizeable temperature differences. This is important where data from different laboratories are compared and we conclude that practitioners should routinely take note of the following points. Firstly, ramping rates should be as low as possible consistent with the optical sensitivity available (there is a trade-off between the two, but temperature differences are likely to be important where ramping rates exceed 5 K s-1). Secondly, it is advisable to use helium as exchange gas rather than the more usual argon, because it is a much better conductor of heat. Thirdly, users should do a few basic thermal experiments with their apparatus so that, with the aid of formulae given in the paper which follows this one, they can make corrections where these are important. This is the first of a linked pair of papers on this subject; it is primarily about experimental results, while the second (following) paper offers some theory which can be applied. (author)