X-Ray-Induced Dislocation Generation in Sodium Chloride

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Abstract
The strain distribution, induced by subjecting one-half of a sodium chloride single crystal to x rays while shielding the other half, has been investigated with a dislocation etch pit technique. Due to the expansion of the irradiated half, a strain gradient arises antisymmetrically about the plane of the interface that is sufficient in magnitude to cause plastic deformation in the protected half, but not in the irradiated half of the crystal. The plastic deformation takes the form of a number of high-density dislocation bands which tend to align in a [100] direction. The bands increase in number but not appreciably in size as irradiation proceeds. The absence of plastic deformation in the irradiated half can be explained by the fact that irradiation raises the yield strength to such a level that the strain is not sufficient to induce plastic flow. In the protected region, however, dislocations are generated and glide until they impinge, causing discrete bands to form roughly parallel to (100) planes. From an analysis of the data, an estimate of the magnitude of the strain produced at the interface and the relationship between the strain and the number of F centers generated can be obtained. The results, although in some ways unexpected, are consistent with previous experiments performed on x-irradiated alkali halides.