Effects of prior neutron irradiation on stress build-up in glass caused by ultra-violet light

Abstract

Ultra-violet light causes compaction of borate and borosilicate glasses, building up stresses in the irradiated surface layers. Assumed mechanisms of the stress build-up are briefly reviewed; they are based on the double bond character of the network of the glasses and the compaction processes start with photoexcitation, charge transfer or photoionisation of B-O or B-O structural units of the glasses.

The effects of prior neutron irradiation on the kinetics of the stress build-up and thermal release of the stress are examined. Prior neutron irradiation gives distinct changes in the kinetics of the stress build-up even at very low doses such as 10⁷ neutrons/cm², causing an additive stress which appears and saturates within the early stage of ultra-violet irradiation. The effects of prior neutron irradiation disappear by successive heating at temperatures lower than 300° C. The stress enhanced by prior neutron irradiation is also thermally released by heating in the same temperature range. The threshold wavelength for the stress in neutron irradiated glass is similar to that in glasses not neutron irradiated.

The π-bond character of the glass network seems to make the kinetics of the stress build-up sensitive to neutron irradiation even at low doses. Prior neutron irradiation forms a region in the glass network in which the stress build-up by ultra-violet light is facilitated, while elsewhere the kinetics of the stress build-up remain unchanged.