Ionizing Irradiation Effects on the Fracture Surface Energy of Potassium Chloride

Abstract

The Co-60 gamma-ray-induced changes in the fracture surface energy φ of KCl at 300° and 115°K, as measured by the Obreimov-Gilman slow cleavage technique, are given by φ=φ0+a1DF12+a2DF23,where φ0 is the fracture surface energy of unirradiated crystal, DF is the F-band optical density per centimeter, and a1 and a2 are constants independent of DF. The square root term represents a plastic-flow contribution which decreases with increasing irradiation and is dominant at room temperature. The two-thirds power term represents an extrinsic, point-defect (EPD) contribution which increases with increasing irradiation and dominates at low temperature. The formation of aggregate centers by room-temperature ``F-light'' bleaching causes an increase in the EPD contribution, which is reversed when the aggregate centers are destroyed by re-irradiation. The external surface energy of Co-60 gamma-ray and 40-kV x-ray irradiated KCl at 300°K, as measured by a pendulum sclerometer, follows a similar relation which is derived under the assumption of a quasistatic friction mechanism. Qualitative observations on spontaneous and forced crack healing in KCl are consistent with the above findings.