Response curves for the thermoluminescence induced by alpha particles: Interpretation using track structure theory

A three dimensional model is developed to describe the linear-sublinear behaviour of the thermoluminescence (TL) dose response curve induced by heavy charged particles specifically 'low energy' ( approximately 1 MeV u ^-1) alpha particles. Supralinearity induced by alpha particles is shown to be suppressed or non-existent owing to the very low probability (<2%) of overlapping tracks in the dose region 10-5000 Gy where electron induced supralinearity is normally observed. Description of the sublinear behaviour is based on calculations using the Monte Carlo as well as analytical methods in which the alpha particle track is described as a cylindrical volume whose height corresponds to the range of the alpha particle and whose effective radius, r_eff, is a single free parameter, determined by fitting the theoretical dose response to experimental results. The calculations are based on the approximation that the sublinear behaviour is a result of overlapping tracks in which the overlapping regions are completely saturated, i.e. the increase in dose in the overlapping volume does not result in an increase in the TL signal. Using this assumption a theoretical dose response curve is obtained which is sublinear at high dose and in excellent agreement with experimental results are shown by chi ²/n values.