GAMMA-RAY INDUCED 11.8 MT ESR DOUBLET IN NATURAL SILICA

We report electron spin resonance (ESR) measurements in natural and sy nthetic vitreous SiO2 samples irradiated by gamma rays. An 11.8 mT dou blet? asymmetrically centered on the resonance line of the E' center, was detected only in natural samples. The intensity of this doublet as a function of gamma exposure tends to saturate for doses as low as 0. 2 Mrad and is not related to the growth kinetics of the E' centers. Ph otoluminescence (PL) measurements on the same samples have shown that two emissions at 3.15 and 4.26 eV bleach with the same kinetics as doe s the 11.8 mT doublet on increasing the gamma ray dose. We tentatively suggest the presence of a conversion mechanism, activated by gamma ir radiation, between the two centers responsible for these optical and m agnetic features. (C) 1998 Elsevier Science B.V. All rights reserved.