Some remarks on the interpretation of natural and magnetically induced optical activity data

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 $\langle $E$_{\text{R}}\rangle $ and transverse $\langle $E$_{\text{R}\perp}\rangle $ average He$^{+}$ recoil-ion-energies are calculated as functions of the laboratory proton scattering angle $\Theta \leq $ 2 mrad. Measurements (Dorner 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.