The saturation of F-centre production in alkali halides under proton irradiation

Abstract

Protons in the energy range 100-400 kev have been used to study the saturation of the stage II intrinsic F-centre production process in alkali halides. In most cases protons in this energy range have well-defined ranges which are proportional to their energy, being about 1?5 ?m in KCl at 100 kev. It is possible, therefore, to produce heavy uniform radiation damage in a very thin layer while keeping the optical density in an accessible region. Stage II F-centre production has been found to saturate at an F-centre concentration of about 10-3 at room temperature, and at a concentration of about 3 ? 10-4 at 4?K. Although the protons do combine with F centres to form U centres this does not contribute significantly as a cause of saturation, which seems to be due to the spontaneous recombination of vacancies and interstitials. The protons are channelled along [100] and other symmetry directions and the channelled particles lose energy by electronic excitation at a rate which is smaller than for non-channelled particles.