Investigation of ESR, TL and positron annihilation in -ray irradiated magnesium sulphate

Abstract

The thermoluminescence (TL) glow curves, electron spin resonance (ESR) spectra and positron lifetime spectra in anhydrous magnesium sulphate powder after -irradiation are presented. The ESR isochronal annealing characteristics of -irradiated samples show that the peak f -) attributed to radicals does not decay after annealing at . The TL glow curves obtained at a heating rate of were deconvoluted into four elementary peaks at , , and based on the general-order kinetics equation. The trap parameters, including activation energy E, frequency factor S and kinetics order b, for each peak were obtained by using the initial values estimated from the variable heating rate method before fitting. The TL and ESR dose-responses of in the range from 1 Gy to 20 kGy at room temperature are obtained and fitted with a dose response function to provide nonlinear characteristic parameters, one action factor R and characteristic dose . It is shown that the ESR dose-response for peak f - attributed to radicals is sublinear, while for peak g - attributed to radicals it remains linear. TL dose-responses for the four glow peaks are supralinear. It is therefore assumed that the generation of TL events undergoes a complex, multistage process in which not only anion radicals but also vacancies and impurities might be involved. This argument is supported by the positron lifetime parameters of samples, also obtained in this work.