Neutron irradiation effects in amorphous SiO₂: optical absorption and electron paramagnetic resonance

Abstract

Optical absorption spectra of as-grown and neutron-irradiated amorphous SiO2, both fused natural quartz and synthetic silica, have been analysed in the ultraviolet region below the fundamental edge. The description of the optical spectrum has been further clarified by a detailed study of the spectral components as a function of the neutron irradiation in different types of silica; we have verified known correlations between optical bands and between bands and paramagnetic centres. In 'as-grown' fused quartz samples, a previously unreported band at 6.2 eV has been detected. 'As-grown' synthetic silicas do not show any band, up to the intrinsic absorption edge. In the irradiated samples, the experimental results suggest a correlation between two bands at 5.8 and 7.1 eV, while previous attribution of the bands at 5.0 eV (B-2 band) and 7.6 eV (E band) to the same defect is discussed. The role of impurities in the optical absorption and in the radiation hardness is also considered.