The mechanism of radiation-induced compaction in vitreous silica

We describe vitreous silica as a two-phase system. Low-temperature phase A and high-temperature phase B are connected by a solid-state phase transition and the phase transition temperature should be higher than the glass transition temperature. This model is based on the observed volume change induced by hydrostatic pressure, fast neutron, ion, electron and photon radiation, etc. Compaction induced by knock-on radiation in vitreous silica is different from compaction induced by ionizing radiation. For the latter, the observed stretched power dependence of compaction on deposited energy for ionization damage can be explained by applying a simple relaxation model.