Defects in vitreous SiO₂ probed by positron annihilation

Abstract
Annihilation characteristics of positrons in a single quartz crystal and vitreous silica glasses (v-SiO₂) were studied by measurements of two-dimensional angular correlation of positron annihilation radiations. From the measurements, it was found that positrons and positronium (Ps) atoms mainly annihilate from trapped states by vacancy-type defects in the v-SiO₂ specimen. For the v-SiO₂ specimen with a cylindrical porous structure, the annihilation of Ps with anisotropic momentum distributions was observed. This was attributed to the momentum uncertainty due to a localization of Ps in a finite dimension of pores. The present investigation showed possibilities for the detection of microstructures in v-SiO₂ by the positron annihilation technique.