Studies of radiation damage in NaCl single crystals by positron annihilation

Abstract

Aging and heat treatment of NaCl single crystals after high-energy (100 MeV) electron irradiation was studied by positron lifetime and peak counts of two-photon angular correlation techniques. Three lifetime components, τ1≃0.15, τ2≃0.38, and τ3≃1.10 nsec, with I2≃52% and I3≃4.5%, are clearly observed for the sample aged at room temperature after the electron irradiation. Annealing of the sample up to 300 °C has reduced the value of I3 to <1%. As Ta≳300 °C, the long-lifetime component becomes practically unresolvable. The peak counts of two-photon angular correlation N(0) versus the annealing temperature Ta curves also showed a rapid decrease in the region, 125 °C<Ta<200 °C. The extinction of the long-lived τ3 component and the decrease of N(0) were attributed to rediffusion of the Na from colloidal aggregates to lattice sites in the crystal formerly vacant.