Irradiation effects on the absorption edge of silica glass

Vacuum ultraviolet absorption experiments were carried out on a variety of specimens of amorphous silica b-irradiated at different doses from 103 to 5 · 106 kGy. Changes in the width of the absorption (Urbach) edge were investigated. These changes strongly depend on the kind of silica considered: in particular the Urbach energy of silica of industrial manufacture increases in the irradiated samples, whereas in sol–gel silica it is poorly influenced by the irradiation. The fictive temperature of the different materials before and after irradiation was also monitored. The changes of the Urbach energy and of the fictive temperature are tentatively discussed considering the disorder degree induced by irradiation.