Growth kinetics of AlOHC defects in γ-irradiated silica glasses

Electron paramagnetic resonance (EPR) measurements have been carried out on various types of natural fused silica (I301, Q310 and H102) irradiated with gamma-ray doses up to 14 MGy. Paramagnetic defects E′γ as well as the non-bridging oxygen-hole centre (NBOHC), the peroxide radical (POR) and the aluminium oxygen-hole centre (AlOHC) account for all lines observed in the EPR spectra of irradiated samples. The growth kinetics of AlOHC has been followed and analysed. It is found that AlOHC defects are produced by two processes. One of them, called rapid process, saturates at low doses and has been related to the precursor {AlO4−/H+}, H+ acting as charge compensator. The second one, called slow process, takes place up to the highest dose and has been related to the precursor {AlO4−/M+}, the compensator M+ being an alkaline-earth ion Li+, Na+ or K+.