DEFECTS IN ELECTRON-IRRADIATED VITREOUS SIO2 PROBED BY POSITRON-ANNIHILATION

Defects in 3 MeV electron irradiated vitreous SiO2 (v-SiO2) were probed by the positron annihilation technique. For unirradiated v-SiO2 specimens, almost all positrons were found to annihilate from postronium (Ps) states. The high formation probability of Ps was decreased by the electron irradiation. The observed inhibition of the Ps formation was attributed to the trapping of positrons by points defects introduced and/or activated by the irradiation. From measurements of the lifetime distribution of Ps, it was found that, by the electron irradiation, the mean size of open-space defects was decreased and the size distribution of such defects was broadened.