Exotic Nuclear Deformation and the Evolution of Nuclear Structure with Angular Momentum and Excitation Energy in ¹⁵⁷Ho, ¹⁶⁶Er, and ¹⁶⁹,¹⁷⁰Yb

Nuclei in the light rare-earth, for values of N ≥ 90, are textbook examples of the evolution of nuclear structure with respect to excitation energy and angular momentum in deformed nuclei. In the high-spin region (J ≥ 10ħ), effects such as backbends and shape changes occur, ending with termination of the lower energy collective structures. First backbends occur before 20ħ Findings also reflect a spectacular return to collectivity in the "ultra-high spin" region (J ≥ 50ħ). Thanks to recent developments in both detectors and accelerators, gamma-ray spectroscopy has been able to probe the upper ends of the high-spin region, and begin probing into the ultra-high spin regime. Data from two experiments form the basis of this work. One study was an ultra-high-spin analysis of the Z=67, N=90 ¹⁵⁷Ho nucleus at Argonne National Laboratory with Gammasphere. The findings were that remarkable correlations were observed to the neighboring isotone, ¹⁵⁸Er, in which termination states and ultra-high spin structures had been previously observed. A high-spin investigation of Ytterbium (Yb) and Erbium (Er) isotopes was performed at FSU. This study used an intense radioactive ¹⁴C beam, available at FSU, in order to study these heavy, neutron-rich nuclei in regions of angular momentum and excitation energy not attainable with stable beams. The reactions of ¹⁷⁰Er(¹⁴C,5n/4n/α4n) generated new information in ¹⁶⁹Yb, ¹⁷⁰Yb, and ¹⁶⁶Er, respectively. Due to the recently upgraded digital FSU Gamma-Ray Array, aided by JBSMILE, triple ᵧ-ray coincidences were able to be viewed in these nuclei for the first time at FSU. The result was the investigation of rotational alignments in both the yrast and non-yrast multi-quasiparticle bands in these nuclei.