Positron as a Probe of Imperfections in Quartz Crystals

Abstract

The angular correlation between the two γ quanta emerging from positron annihilation in quartz crystals shows a structure with intensity S = NC + FS composed of a narrow component NC and a fine structure FS, which is characteristic of the symmetry of the quartz crystal. This structure, where the ratio NC/FS remains nearly constant, is sensitive to certain types of imperfections present or created in the quartz samples. Thus, slow growth rate, high Q, and low concentrations of aluminum or alkali impurities enhance S, while electron or neutron irradiation decreases S, which can be restored to its initial value by optical bleaching or thermal annealing of color centers created by irradiation.