THE (GAMMA,P) REACTION AT E-GAMMA SIMILAR-TO-60 MEV

A study of the (gamma, p) reaction on C-12, N-14, Al-27 and V-51 targets. at photon energies E(gamma) approximately 60 MeV, is reported. Angular distributions in the range t(p) = 60-degrees - 120-degrees are presented for transitions leading to the ground state and several low-lying states in each residual nucleus. The relative population of residual nucleus states is similar to those found in (e,e'p) and (d, He-3) experiments, apart from the well-known exception of the peak at 6.8 MeV in the C-12(gamma, p) reaction. Direct-knockout calculations fail to account for the magnitude of the (gamma, p) results, which indicates the need for calculations that include effects such as meson exchange or short-range correlations. Strength seen at higher excitation energies is attributed to inclusive (gamma, p) events. The excitation-energy spectra have been compared with quasi-deuteron model calculations which assume a (gamma, np) reaction where the neutron goes undetected. The shape of the V-51(gamma, p) excitation spectrum is compared to a pre-equilibrium model calculation. The results appear to indicate that two-nucleon absorption of the photon is important.