Interactions of 28-Mev Protons with Helium-4

Abstract

When ${\mathrm{He}}^{4}$ 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, ${\mathrm{He}}^{4}(p, 2p){\mathrm{H}}^{3}$ and ${\mathrm{He}}^{4}(p, pn){\mathrm{He}}^{3}$, have cross sections of 8.9\ifmmode\pm\else\textpm\fi{}1.0 and 4.8\ifmmode\pm\else\textpm\fi{}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---($p, \mathrm{pd}$), ($p, n2p$), ($p, p\ensuremath{\gamma}$)---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 $\ensuremath{\gamma}$-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 ${\mathrm{He}}^{4}(p, 2p){\mathrm{H}}^{3}$ reaction shows no evidence of an excited level in ${\mathrm{He}}^{4}$ in the energy region explored.