Neutron captures in the r-process : Do we know them and does it make any difference?

Abstract

Nucleosynthesis of elements beyond the iron peak requires reactions with neutrons due to the high Coulomb barriers which prevent charged particle reactions. Approximately half of the intermediate and heavy elements are created in the r–process with neutron number densities nn > 1022 cm−3, effective neutron energies around 100 keV, and short process times of up to a few seconds. These conditions point to an explosive site but the actual site has yet to be identified. Self-consistent SNII models show persistent problems in explaining r–nucleosynthesis. In consequence, most r–process investigations focus on simplified, parameterized models which allow to study the required conditions and their sensitivities to nuclear inputs. Due to the high neutron densities the r–process synthesizes very neutron-rich nuclei far off stability which subsequently decay to stability when the process ceases due to lack of neutrons or low temperatures. This raises the question whether we can predict reactions far off stability sufficiently well to make statements about r–process conditions.