NEUTRON-IRRADIATION EFFECTS IN QUARTZ - OPTICAL-ABSORPTION AND ELECTRON-PARAMAGNETIC RESONANCE

Optical absorption measurements in the 3-9 eV energy range and electron paramagnetic resonance (EPR) have been performed at 300 K and at 80 K on Sawyer PQ quartz. Both as-received and neutron-irradiated samples (neutron fluences up to 3 x 10(18) neutrons cm-2) have been studied. The absorption spectra have been analysed in terms of a sum of elementary Gaussian components. The effect of the neutron irradiations is to induce the presence of absorption bands al 7.6 eV (E band), at 7.1 eV (D band) and at 6 eV (E' region). The most intense peak of all the spectra is the E band (7.6 eV); its shape is complex and the existence of a double structure can be suggested. The D band is evidenced for the first time in neutron-irradiated synthetic quartz; our measurements show that this structure is correlated with the 6.0 eV band. The 'E'' region is complex; in fact, at the highest neutron fluence the optical absorption spectrum reveals the existence of four structures, at 4.7, 5.2, 5.6 and 6.0 eV, where the 4.7 eV band has the same characteristics as the D0 band, which is present in amorphous silica. The comparison between the results of EPR measurements and the analysis of the complex structure of this absorption indicates that the correlation between optical absorption bands in this region and the EPR E'-centre signals suggested previously must be re-examined.