Correlated defect creation and dose-dependent radiation sensitivity in amorphousSiO2

Electron-spin-resonance studies have been made of the kinetics of γ-ray-induced defect creation in samples of undensified, low-OH-concentration (<5 ppm) and high-OH-concentration (>1200 ppm) silica and in samples plastically densified by 12.3% (low OH) and 13.8% (high OH). For the oxygen-vacancy defect, $E_1^{\mathcal{’}}$, creation is enhanced by a factor ∼350 for high-OH-concentration samples and by ∼200 for low-OH-concentration samples for a dose of 0.2 Mrad after densification. Nonbridging oxygen-hole center defect creation in high-OH-concentration silica is enhanced by ∼50 times, essentially independent of γ-ray dose for the range studied (<8 Mrad). Arguments are advanced for a process of correlated defect creation via strained-bond cleavage in densified silica, while in undensified silica defects are created by radiolysis of OH bonds and oxygen displacement through ionizing-energy-related processes. It is concluded that the $E_1^{\mathcal{’}}$ defects observed in densified silica are consequently only the paramagnetic part of the usual oxygen-vacancy defect.