Date of Award
Doctor of Philosophy
Miguel Madurga-Flores, Nadia Fomin, Lawrence Heilbronn
Studies of beta decays can give insights into the underlying structure of the nucleus. In particular, decays of closed-shell and near-closed-shell nuclei can provide important benchmarks for structure models, which are used in simulations of r-process nucleosynthesis. This work reports on a study of beta decays of 71Co produced in an experiment that was carried out in October 2016 at MSU’s National Superconducting Cyclotron Laboratory (NSCL) using the Versatile Array of Neutron Detectors at Low Energy (VANDLE). In order to carry out this experiment, a novel position-sensitive scintillating detector was developed to enable the sub-nanosecond timing response that VANDLE requires, which traditional silicon-based position-sensitive detectors would be unable to provide. This experiment marked the first time that VANDLE was used in a decay spectroscopy experiment at a fragmentation facility.
The beta decay strength distribution for 71Co beta decay is determined above the neutron separation energy in 71Ni, and direct measurement of the beta-delayed neutron branching ratio is reported. The neutron branching ratio is higher than found in past measurements that sought to estimate it by measuring gamma-ray coincidences. Shell model calculations can explain the experimental data only when an effective Z=28 Shell gap is less than 2 MeV in 71Ni, a significant reduction over the 5 MeV expected near 78Ni.
Keeler, Andrew, "The structure of 71Ni via beta-delayed neutron spectroscopy of 71Co. " PhD diss., University of Tennessee, 2022.