Applicability of the mobile interstitial model for thermoluminescence in LiF TLD-100 at medium and high dose levels

Abstract

Optical absorption (OA) and thermoluminescence (TL) studies in LiF TLD-100 single crystals at high gamma-ray dose levels tend to support the validity of the mobile interstitial model in explaining the dependence of the glow curve shape with gamma-ray dose. Especially the disappearance of the dosimetric peak (peak no. V) at about 225°C and other low temperature peaks above 25°C at high gamma-ray dose levels (> 10 5 Gy) is accompanied by the disappearance of the respective OA bands at 310 and 380 nm. At the highest dose studied, LiF TLD-100 exhibits a TL peak at about 350°C (peak no. VIII) whose annealing step coincides with that of the 250 nm OA band which confirms the composite nature of this band. Dose levels greater than 7.2 ×10 3 Gy result in the growth of F-aggregate centres with their characteristic OA bands at 448 nm (M centre) and at 378 nm (R 2 centre). However, detailed studies on the OA spectra of TLD-100 indicate that the mobile interstitial model in its present form does not explain satisfactorily the supralinearity in the response of different TL peaks seen in the medium dose range (10–10 3 Gy). OA results tend to support the competing nonluminescent centre model at least for peak V which envisages a part of the charge released during TL readout to be trapped by these competitors, and indicate that more than one TL process operate simultaneously in this material.