Radiation Effects in Silica at Low Temperatures

Optical absorption bands induced in fused silica and crystalline $\ensuremath{\alpha}$ quartz of low impurity content at 77\ifmmode^\circ\else\textdegree\fi{}K by fast electrons or x-rays bleach slowly at room temperature. The presence of O${\mathrm{H}}^{\ensuremath{-}}$ ions in fused silica inhibits the formation of such radiation-induced absorption. Comparison of the number of centers produced at 215 m\ensuremath{\mu} ($C$ band) in Corning 7943 fused silica (O${\mathrm{H}}^{\ensuremath{-}}$ free) for equal absorbed dose when irradiated with electrons and x-rays indicates that displacements are not involved in the initial formation of the color centers. A defect model requiring simple ionization seems adequate to explain most of the observed phenomena in this pure fused silica. No simple model can be proposed which adequately describes the data in the case of the Corning 7940 fused silica (O${\mathrm{H}}^{\ensuremath{-}}$ bearing).