Neutrons play a crucial role in astrophysics during the heavy element nucleosynthesis. The largest fraction of isotopes heavier than iron is produced by neutron capture processes on short (r process) and long timescales (s process).

During the “slow neutron capture process” (s process) heavier elements are produced by successive captures of in-situ produced neutrons from the reactions 13C(alpha,n)16O and 22Ne(alpha,n)25Mg (with densities of 106-1010 cm-3) in the interior of stars and following beta-decays. With this scenario the reaction path runs along the valley of stability up to 209Bi and produces about 50% of the solar abundances of the heavy elements.

The “rapid neutron capture process” (r process) is responsible for the remaining 50% of the solar abundances. Here neutrons with densities of 10^20-10^30 cm-3 are captured on a very fast timescale (ms) during a Core Collapse Supernova in a region close to the forming neutron star. The r-process isotopes are thus very short-lived, neutron-rich isotopes up to the actinides region. These isotopes can only be produced and investigated at large-scale facilities like the GSI in Darmstadt. Here the most important nuclear physics parameters are for example masses, half-lives, and at later stages also beta-delayed neutrons.

This talk will summarize the role of neutrons in nuclear astrophysics and give a short overview about the related astrophysics program at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt the future FAIR facility.

This work is supported by the German Helmholtz association via the Helmholtz Young Investigator projects VH-NG-627.