Annealing of Irradiation Effects in Sodium Chloride Irradiated with High-Energy Protons

Abstract

Single crystals of sodium chloride were subjected to irradiation at room temperature by 350-Mev protons with a total flux of ${10}^{12}$ to ${10}^{16}$ protons per ${\mathrm{cm}}^2$, and changes in their electrical conductivity, stored energy, and optical absorption were studied. The relative resistivity changes due to irradiation were measured during warmup at a rate of 2°C/min, showing maxima at around 150°C and 250°C and annealing out at about 400°C. The stored energies released during annealing were measured in the same temperature range. The results indicate the presence of three stages of annealing, the first lies between room temperature and 150°C, the second between 150°C and 250°C and the third is above 250°C. The stored energy curve has maxima at 100°C, 200°C, and 310°C. The probable mechanisms of the various annealing processes are discussed. In particular specific mechanisms are proposed for the second stage of the annealing in which significant changes of the optical absorption bands take place. Efficiency of the production of defects was estimated to be the order of ${10}^3$ per proton per centimeter path and this is compared briefly with the theories of Seitz and Smoluchowski.