THE UNIFIED INTERACTION-MODEL APPLIED TO THE GAMMA-RAY INDUCED SUPRALINEARITY AND SENSITIZATION OF PEAK-5 IN LIF-MG,TI (TLD-100)

We describe the development of a comprehensive theory of thermolumines cence (TL) supralinearity and sensitization, the unified interaction m odel (UNIM), based on both radiation absorption stage and recombinatio n stage mechanisms. The UNIM incorporates both the track interaction m odel (TIM) for heavy charged particles (HCPs) and the defect interacti on model (DIM) for isotropically ionizing gamma rays and electrons, in a unified and self-consistent conceptual and mathematical formalism. The model is applied to explain the unique features of gamma-induced s upralinearity and sensitization of peak 5 in LiF:Mg,Ti, especially the strictly linear, then supralinear behaviour and the dependence of the supralinearity on ionization density (gamma ray energy and particle t ype). Both features arise from a localized trapping entity (the track for HCPs, spatially correlated trapping centres and luminescent centre s (TC/LC pairs) for gamma rays and electrons, which dominate the dose response at low dose and are not subject to intra-track competitive pr ocesses, thus leading to linear dose response behaviour. The decreasin g efficiency of the competitive processes relative to the luminescence recombination processes, as a function of dose, leads to the supralin ear behaviour. The decrease of the supralinearity with decreasing gamm a ray energy (increasing ionization density) arises from the increasin g probability of the TC/LC pair to simultaneously capture an electron- hole pair, leading to geminate recombination not subject to competitiv e processes. The UNIM is shown to be capable of yielding excellent fit s to the experimental data with many of the variable parameters of the model strongly constrained by ancillary optical absorption and sensit ization measurements.