INDUCED OPTICAL-ABSORPTION IN GAMMA, NEUTRON AND ULTRAVIOLET-IRRADIATED FUSED QUARTZ AND SILICA

We have investigated the effects of ultraviolet (4.7 eV), gamma (simil ar to 1 MeV), and neutron (similar to 1 MeV) irradiations on the optic al properties of SiO2 glass samples. Samples from various sources were studied, including synthetic fused silicas and natural fused quartz. Several relationships among the different types of ionizing radiation were examined. For example, both UV light and gamma rays convert the g ermanium impurity to the B, absorption band in fused quartz samples. O n the other hand, only neutrons are capable of inducing the oxygen def icient centers (ODCs) with the similar to krad-level doses employed he re; the ODCs are produced by way of direct knock-on collisions. The OD Cs generated by the neutrons can be converted into E' centers afterwar ds with gamma-rays. Transient grating and pump-probe optical experimen ts show that only a small fraction of the induced defect absorption re mains permanently, while nearly all recover to the original condition after a UV pulse. Finally, thermal annealing experiments indicate that the radiation-induced defects can be annealed away at temperatures >3 50 degrees C. We compare the impacts of gamma, neutron, and ultraviole t radiation in terms of the mechanism by which defects are generated.