The track interaction model for alpha particle induced thermoluminescence supralinearity: Dependence of the supralinearity on the vector properties of the alpha particle radiation field

Thermoluminescence (TL)-fluence response characteristics for peaks 5, 7, 8 and 9 in LiF:MS,Ti (TLD-100; Harshaw/Bicron) were measured for 5 MeV alpha particles, in both 'non-parallel' and 'near-parallel' geometries,and for 1 MeV alpha particles in 'near-parallel' geometry. The onset of supralinearity in the non-parallel configuration is always at a significantly lower fluence (by approximately a factor of five) than in the nearly parallel configuration. This dependence of the onset of supralinearity on the vector properties of the alpha particle radiation field is interpreted as 'proof positive' of the dominant importance of track interaction effects in the linear/supralinear behaviour of the glow peaks of TLD-100. A mathematical expression for the linear/supralinear behaviour for heavy charged particles in near-parallel geometry has been developed and fitted to the TL-fluence response curves. The model incorporates both possibilities of electron and hole diffusion in the glow curve heating stage as well as the contribution to the supralinearity of all the participating nearest-neighbour track interactions. The model is capable of yielding excellent fits to the experimental data; the inclusion of hole diffusion and retrapping is preferred to predict the very abrupt transition from linear to supralinear behaviour for the high-temperature peaks.