Direct and semidirect radiative capture of nucleons with Hartree-Fock-BCS bound statesL. Bonneau1, T. Kawano1, T. Watanabe1, 2 and S. Chiba3
1 Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
2 Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
3 Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
Published online: 21 May 2008
Nucleon radiative capture is one of the most important process for nucleo-synthesis calculations in astrophysics. The nucleon capture can occur in two different mechanisms: the compound reaction and the direct-semidirect (DSD) process. The compound capture cross sections become very small when many neutron channels open because the neutron width becomes much larger than the γ width. For incident nucleon energies above about 5 MeV, the capture process can be described by the DSD theory only. In the DSD process, the incident particle is captured directly by an unoccupied bound state (direct) or it excites a collective state and is then scattered into a bound state (semidirect). In this picture, the calculation is sensitive to the radial wave functions of the bound state, which are often calculated with a single-particle model using a Wood-Saxon potential. For astrophysical calculations, since experimental information on nuclear structure is uncertain or inaccessible, we apply a Hartree-Fock-BCS (HFBCS) structure model to generate the radial wave functions. The DSD cross sections are obtained by calculating a transition amplitude to the HFBCS states and using the calculated spectroscopic factors. We calculate the neutron capture cross sections for even-even spherical and deformed targets, namely 208Pb, 122,132Sn and 238U. The agreement with the experimental cross sections, only available for 208Pb and 238U, is very good.
© CEA 2008