Channelling of MeV H and He Ions in Alkali Halides at 'Zero Dose' Measurements

Abstract

Measurements of the minimum scattering yield Xmln and the half-angle for channelling 1fI~ have been made for crystals of LiF, NaF, NaC! and KCI at very small total doses of H+ and 4He+ ions. The measured values of 1fI~ are in good agreement with theory. Comparison of the results for Xmln as a function of depth, with theories based on a linear increase of the mean square beam divergence Q2, shows that for the alkali halides studied the initial beam divergence Q o on entering the crystal is proportional to 1f11> the Lindhard characteristic channelling angle.