Nuclear inputs to the rapid neutron-capture process

4 problems

• Fission barriers and fragment yields of r-process actinides

  Open

  In the most neutron-rich environments the r-process builds nuclei heavy enough to split by fission, and the fragments seed lighter elements. How these nuclei split is predicted only by uncertain models.

• Masses and half-lives of $N = 126$ waiting-point nuclei

  Open

  The third abundance peak, near platinum and gold, forms where neutron-rich nuclei with 126 neutrons pause before decaying further. Almost none of these nuclei have been measured.

• Neutron-capture rates on unstable neutron-rich nuclei

  Open

  As matter cools after an r-process event, the rate at which unstable nuclei absorb extra neutrons shapes the final abundance pattern. These rates cannot be measured directly because the nuclei live too briefly to be made into targets.

• Origin of the rare-earth abundance peak

  Contested

  The solar system has a small extra bump in the abundances of rare-earth elements near mass 160. Whether it comes from nuclear deformation (nuclei becoming non-spherical) late in the r-process or from fission fragments is not known.