Diffusion plus Explosion Mechanism of Void-Crack Transition in Irradiated NaCl

Experimental and theoretical results are presented on the formation of large vacancy voids and cracks in NaCl under irradiation. The crack length increases gradually with increasing stored energy, which is explained by a new mechanism of diffusion accumulation and explosive release of energy in voids and cracks. It is shown that the colloid number density, which determines the critical void radius that triggers the explosion process, has a drastic effect on the ultimate mechanical stability of material. If it is low as in NaCl doped with Br then the critical void radius is large and difficult to reach. If it is high as in NaCl:KBF4 it takes a high colloid volume fraction to initiate the void-crack transition, which progresses rather slowly. The materials doped with Ba or K, and natural rock salts show the transitional behavior, which is characterized by an early start and a rapid progress of the void-crack transition, resulting in a subsequent fracture of the material