Interactions of 28-Mev Protons with Helium-4

When He⁴ is bombarded with 28-Mev protons the dominant reaction is elastic scattering, exhibiting a strong peak in the forward direction and a slight rise in the backward direction. The dominant inelastic reaction is the inverse Butler or pickup deuteron process.The two remaining inelastic reactions observed, He⁴(p, 2p)H³ and He⁴(p, pn)He³, have cross sections of 8.9±{}1.0 and 4.8±{}1.3 mb, respectively. These are an order of magnitude or more smaller than the cross sections of the dominant processes.Of the remaining possible reactions---(p, pd), ($p, n2p$), (p, pγ)---only the last was energetically possible at the beam energy used. It was not observed. This indicates a lack of evidence for an excited level that decays principally by γ-ray emission; it also indicates that the inverse photodisintegration process, suggested by Flowers and Mandl, has too small a cross section to contribute in this energy region.The rest-frame momentum spectrum of protons from the He⁴(p, 2p)H³ reaction shows no evidence of an excited level in He⁴ in the energy region explored.