Direct neutron captures and the r-process nucleosynthesis

The radiative direct capture of neutrons is calculated within the potential model. The uncertainties related to the choice of the neutron-nucleus interaction potential and the prediction of the excitation spectrum in the residual nucleus are discussed. The allowed direct E1-type transitions to all the excited states predicted by a combinatorial model of nuclear level densities are calculated with the introduction of an average spectroscopic factor. The resulting direct contribution to the neutron capture rate is estimated for all the neutron-rich nuclei potentially involved in the r-process nucleosynthesis and compared with the statistical compound nucleus contribution. The total radiative capture cross section is approximated and used in parametric r-process calculations to study the impact of the direct capture mechanism on the r-process nucleosynthesis.