Evidence of void lattice formation in heavily irradiated NaCl

In this paper we describe new observations on the production of voids and void-structures in heavily irradiated NaCl under electron irradiation. Until now there is no information about voids in NaCl in the literature. In many irradiated samples voids with sizes between 0.05 and 0.7 mu m have been observed. Very large voids with diameters 1.2 to 5 mu m have been found in heavily irradiated natural rocksalt. The size, shape and distribution of the voids depend strongly on the irradiation dose, the irradiation temperature and the presence of impurities. The small, randomly distributed voids, observed in the earlier stages of the irradiation, transform with increasing irradiation doses into a more or less regular void lattice. The lattice of the voids is similar to the one of NaCl with the same axes. The ratio: void spacing/mean a void diameter is in the range 2 to 7 has been found. We did not observe saturation of the size of the voids up to irradiation doses of 150 Grad. The density of the void lattice did not saturate either.