PRE-EXPONENTIAL FACTOR IN GENERAL ORDER KINETICS OF THERMOLUMINESCENCE AND ITS INFLUENCE ON GLOW CURVES

A model of thermoluminescence kinetics based on a physically meaningful approach shows that the glow curve shapes undergo systematic changes with the change of trap occupancy (dose). In terms of the general order kinetics model it means that the kinetic order changes with sample dose. In parallel to the kinetic order, the pre-exponential factor also changes. In contrast to these results the glow curves calculated from the general order kinetics model show that the peak shape remains nearly constant when the trap occupancy is changed. When appropriately defined, the pre-exponential factor also has a fixed value independent of trap occupancy. In these respects the general order kinetics model, though empirical, seems to describe the glow peak behaviour quite successfully. However, regarding the peak temperature the theoretical results both from the physical as well as the empirical model seem to diverge from the experimental observations when the experimentally determined kinetics is non-first order. In such cases, according to the models, the peak maxima shift with the change in trap occupancy, while in the experimental observations such changes are not evident. The shift in the peak maximum in the non-first order cases of the theoretical models is the result of the pre-exponential factor being effectively changed by the alteration in the trap occupancy. In addition to these findings the paper also includes the possible implications of non-first order kinetics in dosimetric applications.