Change in KCl Lattice by Soft X-Rays

The lattice dimensions of powdered specimens of annealed and unannealed KCl were measured during irradiation by soft x-rays. One set of speciments was allowed to color during irradiation and another group was prevented from coloring by simultaneous white-light illumination. The following observations were made: There was an increase in lattice dimension during exposure for every specimen. No difference existed for speciments which were colored or not colored. Saturation in the change in lattice dimension occurred at a lower exposure for the unannealed specimens than for the annealed specimens. The total increase in lattice dimension was about $\frac{\Delta a}{a}=1\mathrm{}\times {10}^{-5\mathrm{}}$ for all speciments, compared with values given in the literature for maximum changes in length of approximately $\frac{\Delta l}{l}=20\mathrm{}\times {10}^{-5\mathrm{}}$. The difference indicates production of void volume, presumably Schottky defects. The failure to observe a difference between colored and uncolored specimens may be caused by a considerably larger production of Schottky defects than of color centers.