A model for non-monotonic dose dependence of thermoluminescence (TL)

Abstract

In the applications of thermoluminescence (TL) in dosimetry and archaeological andgeological dating, a desirable dose dependence of TL intensity is a monotonically increasingfunction, preferably linear. It is well known that in many dosimetric materials, nonlineardependence is observed. This may include a superlinear dependence at low doses and/orsublinear dose dependence at higher doses, where the TL intensity approaches saturation.In quite a number of materials, non-monotonic dose dependence has been observed, namely,the TL intensity reached a maximum value at a certain dose and decreased at higher doses.This effect is sometimes ascribed to ‘radiation damage’ in the literature. In the presentwork we show, both quasi-analytically and by using numerical simulation, that such dosedependence may result from a simple energy level scheme of at least one kind oftrapping state and two kinds of recombination centres. One does not necessarilyhave to assume a destruction of trapping states or recombination centres at highdoses. Instead, the main concept involved is that of competition which takes placeboth at the excitation stage and the read-out stage during the heating of thesample. This may explain the fact that the phenomenon in question, although veryoften ignored, is rather common. Cases are identified in which competition duringexcitation dominates, and others in which competition during read-out dominates.