Extracting fission barriers in the Pb region from simultaneous fits

An experiment in summer 2020 at the National Superconducting Cyclotron Laboratory measured the fission properties of nuclei in the neutron-deficient Pb region. A goal of this work was to extract fission barriers from the measured fission cross-sections. The two dominant decay modes for an excited nucleus in this region are fission and neutron emission. As the internal energy of the nucleus before decay (excitation energy) approaches the fission barrier from above, the cross-section drops off exponentially. The fission barrier of a nucleus can be extracted from fission cross-sections using a statistical decay model parameterized by the fission barrier, and the level densities of the compound nucleus both at the scission point and post neutron emission. As the experimental data does not go to low excitation energies and the model becomes more sensitive to the fission barrier at low energies, information from multiple nuclei was required to constrain the problem. We hypothesized that the level density parameters could be modeled as a function of the mass number for a region of the chart of nuclides. By simultaneously fitting a set of existing cross-section data in the Pb region, we verified this assumption and extracted a model for the level density parameters.