Ionization Expansion of Compacted Silica and the Theory of Radiation-Induced Dilatations in Vitreous Silica

Abstract

Vitreous silica compacted by pressure at room temperature expands at a very rapid rate when irradiated with soft x rays or in a reactor, about in the ratio of the ionization doses received. A dose \ensuremath{\sim}\textonehalf{} ${10}^{22}$ eV/${\mathrm{cm}}^{3}$ (i.e., ${10}^{8}$R) of absorbed ionization energy caused the "release" of about 1/3 of the compaction.It is shown that the effect cannot be explained as a static electrostatic effect or a transient general thermal annealing effect (thermal spike). It must be a rapid transient effect associated with the local distortion or energy deposition of the ionization event. The efficiency of the process indicates that each ionization in moderately pressure-compacted silica (4-9%) must be effective or multiply-effective in "releasing" compaction. The relation of the compacted states of silica---pressure compacted, radiation compacted, shock wave compacted---is discussed.