Charge trapping mechanisms and microdosimetric processes in lithium fluoride

Abstract

We present a review of the charge trapping and recombination mechanisms in LiF thermoluminescence (TL) dosimeters and discuss several dosimetric properties of this material in the light of these processes. The complex TL glow-curve from LiF doped with Mg, Ti and OH impurities consists of several individual peaks which emit in the region of 420–460 nm, depending on the glow peak temperature. The kinetics of the process appear to be first-order. From an accumulation of experimental data from a variety of sources (dielectric loss, ionic thermocurrents, ionic conductivity, photoluminescence, X-ray-induced luminescence, optical absorption, electron spin resonance, and others) it is inferred that the TL emission near 200°C is the result of electron-hole recombination at defect complexes consisting of Mg trimers and TiOH n centers. The spatial localization of the Mg defects and the Ti defects is seen to be of fundamental importance in describing certain aspects of the dose response function of this material and the stability of the TL signal. Coupled with this, however, the microscopic processes of energy deposition, in which regions of high ionization density are formed inside the irradiated sample, are seen to provide the essential framework around which it is possible to establish a model to describe all the major features of the dose response function in LiF:Mg, Ti, OH for a variety of irradiation types.