Abstract
The structure of the doubly-odd180 Re nucleus has been studied by means of in-beam gamma-ray spectroscopy at the Australian National University. Excited states in 180 Re have been populated using the fusion-evaporation reaction 174Yb(11B,5n) at a bombarding energy of 71 MeV. Gamma-rays have been observed by using the CAESAR detector array which consists of six Hyper-Pure Germanium (HPGe) detector and two Low Energy Photon Spectrometers (LEPS). The level scheme of 180 Re was established from the analysis of gamma-gamma coincidence relations, Directional Correlations of gamma-rays from Oriented states (DCO), electron conversion measurements and gamma-ray intensity balances. Energy levels of intrinsic states have been compared with calculations based on the Blocked BCS (BBCS) theory as well as Potential Energy Surface (PES) calculations which were also used to determine the nuclear shape. Previously identified bands have been observed in this work. Their band-head spins, however, have been reassigned. Their assignment was done on the basis of the BBCS calculations, g-factors, and potential energy surface calculations. Two high-K rotational bands have also been observed, together with a new isomer, with a mean-life of 13?s. This isomeric level was assigned a Kpi=21- band head. It has one of the new rotational bands associated with it and the second one feeding into it. This second band was tentatively assigned a Kpi=22+ configuration. Both the configurations of these bands involve the 9/2+[624] and 7/2- [514] Nilsson states which are coupled to the same protons, 5/2+[402]9/2-[514]7/2+[404] respectively, with only the third neutron, 5/2-[512] for Kpi=21- and 7/2+[633] for Kpi=22+, differing. The experimental aligned angular momenta for these bands increase as the spin increases. Prom this increase it is concluded that these high-K bands gradually change their structure from deformation aligned to rotation aligned through the Fermi aligned scheme as spin increases. During the change of the structure, the quasiparticles which form high-K states at the band heads change their direction of angular momentum from the symmetry axis to the rotation axis due to the effect of the Coriolis force. A number of K-forbidden transitions have been found in this work. Their decay can take place due to K-mixing. Statistical level mixing for Kpi=13+ and Kpi=21- isomeric states was employed in this work to explain the K-mixing process. 180Re is the highest-Z, deformed odd-odd nucleus that has been found to have a six-quasiparticle isomer; K remains approximately a good quantum number despite a tendency towards axially asymmetric shape distortions.