Channeling of positrons

Abstract

A beam of 1.2–MeV positrons was obtained by accelerating in a 1–MeV Van de Graaff positrons emitted by ⁵⁸Co. Channeling in thin silicon crystals was studied by measuring as a function of incidence angle the yield of positrons scattered through a few degrees into an annular detector. The measured axial and planar dips are compared partly to channeling dips in scattering yield for protons of corresponding energy, partly to classical calculations as well as calculations based on the dynamical theory of electron diffraction. In general, the results support the conclusion of a previous study of positron channeling in gold, that channeling of positrons may essentially be described by classical mechanics. In the present measurement, however, fine structure due to interference is clearly resolved. Also, for very weak planes, a complete departure from classical estimates is observed. Finally the dechanneling rate has been studied for axial channeling by measuring the dip in crystals of different thicknesses. It is found to be very close to the dechanneling rate for protons of similar energy, in contrast to the anomaleously slow rate indicated by the work of Behnisch, et al.