NEUTRON-IRRADIATION EFFECTS IN AMORPHOUS SIO2 - OPTICAL-ABSORPTION AND ELECTRON-PARAMAGNETIC-RESONANCE

Optical absorption spectra of as-grown and neutron-irradiated amorphou s SiO2, both fused natural quartz and synthetic silica, have been anal ysed in the ultraviolet region below the fundamental edge. The descrip tion of the optical spectrum has been further clarified by a detailed study of the spectral components as a function of the neutron irradiat ion 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 e xperimental 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 impur ities in the optical absorption and in the radiation hardness is also considered.