Thermoluminescence isothermal decay in γ-irradiated CaSO4 : Dy phosphors—kinetics, and distribution of trap depths

In this paper our experiments on isothermal decay of thermoluminescence of the main peak of CaSO₄ : Dy phosphors at various temperatures and ⁶⁰Co γ doses are described. The decays are not monoexponential; however, as the shape of the decay curves at a same temperature is dose independent, first-order kinetics may be assumed. Consequently, the decay curves at 100 rad are broken down in exponential terms and for each term the decay constant and the related partial light sum are obtained. These results are interpreted, at first, by trying to associate with the peak a multilevel distribution of trap depths; however, the activation energies and the frequency factors for these levels are physically unacceptable. Subsequently, on the hypothesis of a continuous trap distribution, the decay curves are best fitted as a whole; in this way a frequency factor of 3 × 10¹² s⁻¹ and a trap distribution with an approximately gaussian main peak centred at about 1 > ṡ37 eV and three other minor peaks are obtained. To check the consistency of the results, a theoretical glow curve is synthesized and a single peak fairly similar to the experimental one emerges.