Kinetic characterization of the first peak of natural fluorite from low dose β-irradiation
The low temperature peak (PI) of natural fluorite which occurs at 94oC at the heating rate of β = 1 Cs-1exhibits complexity both in terms of shape and position as the absorbed dose is varied. The short lifetime of this peak makes it a good case for testing the existing thermoluminescence kinetic models. In this paper, the kinetic parameters of PI, namely the activation energy, EA , the frequency factor, S, and the order of kinetics, b, have been evaluated using general order kinetics. Fluorite samples were irradiated with a low dose-rate (40 μGys-1 ) β- irradiation source to a test dose of 1.2 mGy and the heating rates of β = 1,3 and 5o Cs were considered, in order to minimize the effect of temperature lag. The role of thermal quenching (W) was investigated by evaluating the activation energy using the initial rise (IR) method for each of the heating rates. The obtained values of kinetic parameters are EA = (1.31 ± 0.06) eV and S = (8.34 ± 1.00) × 1016 s-1 while values of b ranging from above 1.0 up to 1.4 were in good agreement. The value of W = (0.30 ± 0.04) eV was obtained for the thermal quenching function and its contribution was found to be most significant at the heating rate of β = 5so C s-1 .
Keywords: low-dose β-irradiation, first peak of natural fluorite, general-order kinetics, thermal quenching function, peak lifetime.