Generation of a 7.4 mT ESR doublet induced by gamma rays in amorphous-SiO2

Paramagnetic defects induced by gamma rays, in a dose range from 1 to 1000 Mrad, have been investigated by electron spin resonance (ESR) spectroscopy in various types of natural and synthetic silica, having different OH conte nt. A doublet with a field splitting of 7.4 mT, arising from the hyperfine interaction of an unpaired electron with a H nucleus associated with the H( I) center, was detected in all the investigated samples. This ESR structure exhibits a sublinear growth with the gamma dose linearly correlated with t he gamma-induced photoluminescence band at 4.4 eV. The intensity ratio of t hese two signals depends on the OI-I content of the sample. Our results agr ee with a model in which the H(I) center is generated by the reaction betwe en a two-fold coordinated Si and a hydrogen atom activated by the gamma-ind uced breaking of an OH bond. (C) 2000 Elsevier Science B.V. All rights rese rved.