DIFFERENT HARDENING BEHAVIOR OF LOW AND HIGH DOSE GAMMA-IRRADIATED NAC1 SINGLE CRYSTALS

The characteristics of glide at the onset of plastic flow have been determined by etch-pit observations for γ-irradiated NaCl and they have been correlated with stress-strain behavior. A marked difference between low (≲ 106 R) and high (≳ 106 R) dose irradiated samples has been found. The variation of the yield stress σ0 with dose has been determined for both regions of dose. For low dose irradiations a definite hardening exists which can be correlated with the first and second stages of the F-center coloring curve. In particular, the experimental data suggest that only the slow component of the first stage F-coloring contributes to the hardening. On the other hand, it has been observed that the bleaching of F-centers is associated with a relatively large (~40%) decrease in the radiation-induced hardening. For high dose irradiations, yield stress data confirm a Fleissher-type law as observed for other alkali halides. The distinctive nature of hardening in each region of dose has been clearly demonstrated by indentation experiments. © 1969.