Angular Distribution of Metastable Hydrogen Formed by Electron Capture in a Helium Target

A study has been made of the angular distribution of scattered particles induced by proton impact on a target of helium. Cross sections are presented for scattering of protons, of neutral hydrogen atoms, and of metastable hydrogen atoms. Impact energies range from 4 to 20 keV; scattering angles are from 0^∘{} to 2.0^∘{}. Measurements of the fractional metastable content of the scattered neutral flux rise from 1% or less at 0^∘{} to as much as 8% at angles of 1^∘{}. Theoretical predictions of the cross sections for scattering of all particles, neutrals and protons, show reasonable agreement with experiments. Theoretical predictions, by Colegrave and Stevens, of the probability for forming a neutral atom disagree with the experimental values by a constant phase factor. Measurements of the probability for forming a metastable atom do not agree with available theoretical predictions.