Study of the kinetics of peak 5 in LiF:Mg,Ti: Dose dependence of the thermoluminescence isothermal decay at 165°C

The question of the order of kinetics of the thermoluminescence (TL) of peak 5 in LiF:Mg,Ti has been subject to considerable controversy over the years. Recently, we have shown that peak shape analysis of post-irradiation annealed TLD-100 at 165°C leads to non-first order kinetics, reaching a value as high as 1.72 ± 0.07 following a 165°C/30 min. post-irradiation anneal. When no post-irradiation anneal is applied, peak shape analysis almost always yields first-order behaviour. Isothermal decay data is equally ambiguous. To begin to resolve this discrepancy (at least at the experimental level) we have studied the isothermal decay of peak 5 at 165°C (presumably cleaned of the low temperature peaks 2-4 by a 165°C/15 min. post-irradiation anneal). The isothermal decay was initiated at four dose levels of 10, 100, 300 and 1000 Gy, and these decays are not even vaguely similar. The initial rate of decay at 10³ Gy is at least 5 times greater than at 10 Gy and the decays are clearly non-exponential. Our data is not consistent with first order decay (b=1) and leads to b=1.82 ± 0.18 using GO model analysis.