(p, α) Reactions Induced by 23-Mev Protons

The ($p, \alpha$) reactions induced by 23-Mev protons in targets of a wide range of atomic number were studied by observing the outgoing alpha particles. Alpha-particle energy distributions and absolute differential cross sections were measured at 30, 60, 90, 120, and 150 degrees. For targets of atomic number ≲50, the energy spectra and angular distributions indicate that most of the alpha particles are produced in compound nucleus reactions; however, there is evidence that the Coulomb barriers of the excited compound nuclei are somewhat lower than those of ground state nuclei. The alpha particles from the heaviest elements and the high-energy parts of the spectra from lighter targets are strongly forward peaked and are produced by direct interaction reactions. Total ($p, \alpha$) cross sections vary from 175 mb for Al to 3.8 mb for Pt.