The (gamma, p) reaction in Au-197

Proton energy spectra of the Au-197(e, P) reaction were measured in the reg ion between 17 and 30 MeV at three angles: 40 degrees, 90 degrees and 140 d egrees. Two prominent bumps were observed in the (gamma, p) spectra convert ed using virtual photon theory. The higher-energy bump shifts with photon e nergies and the lower-energy one stays at 10.5 MeV. The higher-energy bump is much larger at 40 degrees than at 140 degrees; on the contrary the angul ar dependence of the lower-energy bump is small. Neither bump can be descri bed by a statistical calculation. A calculation of a microscopic shell mode l shows that the lower-energy bump is attributed to the decay of proton-par ticle-neutron-hole pairs in the T, states, leaving a neutron hole around th e Fermi surface. The higher-energy bump can be ascribed to the direct-semid irect mechanism. This paper gives the solution to a part of the long-standi ng question about the origin of photo-proton emission in heavy nuclei. (C) 2001 Elsevier Science B.V. All rights reserved.