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

Abstract

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.

A Photodetector for Measurement of Metastable H(2S) in Ion-Atom Collisions

“…The fraction quenched depends on the time the atom spends in the field and, since a range of velocities is being considered, there results a different intensity distribution along the beam path for particle flux at different velocities. Fitzwilson and Thomas (1972) measured this variation and quoted ±5% over the energy range 4-20 keY. The calculated efficiency variation for the design used in this experiment is less than ±2% over the energy range 4-24 keY; these calculations are discussed below.…”

“…(11, 12) (v) The photon detector may be calibrated with a source of radiation which has a polarisation and intensity distribution similar to the light source used in the actual measurement (Fitzwilson and Thomas 1972). For example, using a known total cross section for production of metastable hydrogen, the flux of particles decaying in view of the photon detector can be calculated and thus related to the actual number of photons measured by the detector to give its conversion efficiency.…”