A thermoluminescent (TL) material emits visible photons upon heating after being exposed to ionising radiation. The TL response of materials exposed to heavy charged-particles (HCPs) presents a linear-supralinear-sublinear behaviour as a function of fluence. The range of fluences for which these regions can be identified, and the degree of supralinearity, varies for each particle and its energy. The Track Interaction Model (TIM) [1] has been relatively successful at describing the supralinear response of TL dosemeters to high heavy charged-particle fluences. The analytical formulation of TIM has forced a number of simple assumptions; in particular, the existing formalism can only be applied to parallel incidence of the HCPs.
In this work we present a Monte Carlo simulation (MC-TIM) developed to explain the linear-supralinear-sublinear behaviour of LiF:Mg,Ti (TLD-100). The simulation assumes that supralinearity arises in the heating stage, where liberated charged carders (electrons) migrate to neighbouring tracks and recombine with luminescent centres, producing extra light. As a first approximation, the electrons are assumed to travel radially outwards from the parent track, perpendicular to its trajectory. The probability that the electrons reach neighbouring tracks is represented by the electron mean free path, which depends on the temperature (the higher the temperature, the higher the probability of migration).
The simulation can handle a variety of geometries for both the irradiation (parallel or non-parallel) and the ion tracks (cylinders or cones). The radius of the ion track as well as the electron mean free path are considered as free parameters. The Monte Carlo results are compared with analytical predictions of TIM and experimental data obtained using both parallel and non-parallel geometry. The comparison between MC-TIM calculations and the experimental results has shown excellent agreement in the whole range of fluence studied.