INVESTIGATION OF ESR, TL AND POSITRON-ANNIHILATION IN GAMMA-RAY IRRADIATED MAGNESIUM-SULFATE

The thermnoluminescence (TL) glow curves, electron spin resonance (ESR ) spectra and positron lifetime spectra in anhydrous magnesium sulphat e powder after gamma-irradiation are presented. The ESR isochronal ann ealing characteristics of gamma-irradiated MgSO4 samples show that the peak f (g-factor = 2.0037) attributed to SO3- radicals does not decay after annealing at 400 degrees C, The TL glow curves obtained at a he aling rate of 1 degrees C s(-1) were deconvoluted into four elementary peaks at 144 degrees C, 243 degrees G, 316 degrees C and 368 degrees C based on the general-order kinetics equation. The trap parameters, i ncluding activation energy E, frequency factor S and kinetics order b, for each peak were obtained by using the initial values estimated fro m the variable heating rate method before fitting. The TL and ESR dose -responses of MgSO4 in the range from 1 Gy to 20 kGy at room temperatu re are obtained and fitted with a dose response function to provide no nlinear characteristic parameters, one action factor R and characteris tic dose D-o. It is shown that the ESR dose-response for peak f (g-fac tor = 2.0037) attributed to SO3- radicals is sublinear, white for peak g (g-factor = 1.9976) attributed to SO4- radicals it remains linear. TL dose-responses for the four glow peaks are supralinear. it is there fore assumed that the generation of TL events undergoes a complex, mul tistage process in which not only anion radicals but also Mg2+ vacanci es and impurities might be involved. This argument is supported by the positron lifetime parameters of MgSO4 samples, also obtained in this work.