CDW-EIS Calculations for Recoil Ion Emission in Proton-Helium Collisions

Single ionization of helium atoms in collision with high energy protons is treated theoretically in the continuum distorted-wave eikonal initial-state (CDW-EIS) approximation. The total (ER) and transverse (ER⊥) average He+ recoil-ion-energies are calculated as functions of the laboratory proton scattering angle θ ≤ 2 mrad. Measurements (Dörner et al. 1989, Phys. Rev. Lett. 63, 147-150) of these average energies made for helium gas in equilibrium at 30 K are reasonably well reproduced to within a factor of two, by the CDW-EIS approximation. The CDW-EIS recoil-ion energy distributions are convoluted over a Maxwellian-Boltzmann distribution, to allow for the 30 K thermal motion of the target helium atoms in the experiment.