Elastic Differential Scattering ofHe+Ions by He in the 20-600-eV Range

Abstract

Absolute elastic differential scattering cross sections for ${\mathrm{He}}^{+}$ on He have been measured at relative energies of 20 to 600 eV over an angular range of 1-36°. The ions are extracted from an electron-bombardment source, formed into a ribbon beam by a pair of slits, and scattered in a gas cell containing He. The scattered beam is energy-analyzed and then detected by an electron multiplier. The relative data are normalized to absolute cross sections obtained at small angles using a Faraday cage in place of the multiplier. The effect of geometry, target-particle motion, and inelastic scattering on the angular resolution of the elastic cross sections is discussed. Three distinct interference phenomena are observed: (1) a series of smooth sinusoidal oscillations resulting from interference between the waves scattered from the gerade and ungerade potentials of the molecular ion, (2) rainbow scattering, (3) secondary oscillations at large angles due to nuclear interchange.