Detection of Vacancies Created by X-Rays in Sodium Chloride

The creation of vacancies in sodium chloride by x-rays is detected using optical techniques. The $F$-band absorption produced by ultraviolet irradiation is measured and the band is then optically bleached. The crystal is then x-rayed and optically bleached. The crystal is again subjected to the same ultraviolet radiation as it received prior to x-raying, and the optical absorption of the $F$-band is remeasured. It is found that the sensitivity of a single crystal of NaCl to ultraviolet radiation is enhanced by a factor of 100 after it has been exposed to 40-kvp x-rays at 13 milliamperes for 30 minutes. Experiments are also performed to determine the stability at room temperature of the excess vacancies under visible and ultraviolet radiation.