Beta decay studies of nickel-69 and vanadium-58: Development of subshell gaps within the N = 28--50 shell

In the framework of this thesis, the development of subshell gaps at N = 32 and N = 40 for neutron-rich nuclides within the N = 28–50 shell were investigated.; A conventional beta detection system was used to examine the beta decay properties of neutron-rich nuclei near N = 40. An N = 40 subshell was first suggested for $N6828i40$ by Broda et al. [1] due to the rise of the first excited 2+ state relative to its N − 2 neighbor, 66Ni. The presence of an N = 40 subshell would inhibit the development of collectivity in this midshell region. During this study, a 3.4(7) s isomeric state in 69Ni was directly produced via the fragmentation of a 70 MeV/nucleon 76Ge beam in a 9Be target at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The beta decay of the 1/2− isomer was observed to mainly populate the excited 3/2− state at 1296 keV in 69Cu. By comparing the total number of 69Ni nuclei implanted with the intensities of the beta-delayed γ rays following the decay of the 1/2− isomeric state and the ground state of 69Ni, a 36% upper limit has been extracted for the beta branch from the isomeric state in 69Ni to the ground state of 69Cu. Based on this branching ratio, a small 2p-2h mixture into the ground state of 69Cu may be deduced. This small admixture suggests that the ground state of 69Cu is predominately single-particle in nature and may be described as a proton coupled to a 68Ni core. The dominance of the 68Ni core provides a strong case for the N = 40 subshell.; A new beta detection system was employed to study the decay properties of neutron-rich nuclides near N = 32. The current measurement provides the first conclusive evidence for a significant subshell gap at N = 32. The presence of the N = 32 subshell gap has been attributed to a strong π1f_7/2-ν1f_5/2 proton-neutron monopole interaction. (Abstract shortened by UMI.)...