High dose proton irradiation of alkali halides

Optical measurements have been made of the concentration of F and other colour centres produced in alkali halides by proton irradiation in the energy range 100-400keV. A treatment is given of a model of interstitial-vacancy recombination at high defect concentration which appears to explain many of the features of the approach to a saturation level of defects. At ambient temperatures F-aggregate centre formation is considered as the process which ultimately produces a real saturation in the F-centre concentration. At low temperatures the limiting process is thought to be the formation of substitutional hydrogen ions (U centres) as protons are captured by F centres. The observation of infrared absorption associated with substitutional hydrogen ions confirm that this combination of protons with F centres does occur, and may also contribute to the fall in F centre concentration which follows saturation.