Ryan Winkler
The study of both the microscopic and macroscopic structural evolution of the atomic nucleus is presented in this work. The excited states of the N = 126 isotone 215Ac were investigated at WNSL using the gas-filled recoil separator SASSYER. Recoil-decay tagging of the gamma rays corresponding to the decay of 215Ac after production via a fusion-evaporation reaction was made possible by using the redesigned SASSYER focal plane apparatus, including the addition of a pair of DSSDs and the multi-wire avalanche counter MACY. A number of transitions feeding the 29/2+ isomeric state corresponding to the ([special characters omitted])⊗(πi13/2) configuration were observed and tentatively assigned as decays from the high-spin 35/2 +, 39/2+, and 41/2+ states. Additionally, the decay from the low-lying 13/2+ state, corresponding to a πi13/2 quasiparticle excitation, was observed at 859 keV. This excitation energy is consistent with the systematics of the lighter N = 126 isotones suggesting a decrease in the energy gap between the πh9/2 and π i13/2 orbitals.
High-resolution (p,t) spectroscopy of the stable, even-even Palladium isotopes was performed in the search for signatures of quantum phase transitional behavior. A total of 54 previously unidentified 0+, 2 +, and 4+ states below an excitation energy of 3.5 MeV were discovered in this experiment. No enhancement of the 0+ level density, a signature of first-order phase transitions in nuclei, was observed in the studied isotopes. A theoretical description of the population strengths of excited 0+ states in two-nucleon transfer reactions was investigated within the framework of the IBM. These studies reveal that an enhanced population strength is not exclusive to regions of shape-coexistence but rather is a measure of the magnitude of the “change of structure” from the initial to residual nucleus.