Kinetics and trapping parameters of thermoluminescence in LiF TLD-100-dependence on dose

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Abstract
The authors demonstrate that the order of kinetics of the TL process can change with the dose received by a sample. In LiF the order of kinetics becomes constant only when the dose given to the sample is smaller than the saturation dose by at least an order of magnitude. The order of kinetics followed by glow peaks V (190 degrees C) and XII (385 degrees C) of LiF TLD-100 is determined using two methods: (i) peak shape, and (ii) isothermal decay. The former gives the values as 1.4 for peak V and 1.35 for peak XII and the latter 1.6 for peak V and 1.5 for peak XII. For the saturation exposure of 105 R when no empty traps are available, peak V decays exponentially in the beginning (first-order kinetics) and as the decay progresses the order of kinetics continuously increases. After 3 min of decay at 165 degrees C, when the intensity has fallen to less than 20% of initial value, the order of kinetics stabilises at 1.6. The activation energies E of the two peaks are determined using (i) peak shape, and (ii) initial rise methods. The initial rise method is found to give lower values of E than the peak shape method. This is explained on the basis of a thermal effect on luminescence efficiency.