High-spin triaxial strongly deformed structures and quasiparticle alignments in 168Hf
Yadav, Ram Babu
Dunne, A. James
Winger, A. Jeff
This dissertation research consists of two parts: (i) investigation of quasiparticle alignments at high-spins and (ii) identification of triaxial strongly deformed structures in 168Hf. A γ-ray spectroscopy study was carried out, as well as lifetime measurements using the Doppler-shift Attenuation Method (DSAM). The two data sets used for this research were obtained from experiments at Argonne National Laboratory employing the reaction 96Zr(76Ge, 4n). The decay γ-rays were measured with the Gammasphere Compton-suppressed Ge spectrometer array. A self-supporting 96Zr foil ("thin target") was used in the first experiment, while in the second experiment the 96Zr target material was evaporated onto a thick Au backing ("backed target" or "thick target") to stop the recoiling nuclei for lifetime measurements. All previously known rotational bands have been extended to higher spins. Seven new normal-deformed bands, of which three are high-K bands, have been discovered. Neutron alignments were observed in all bands, and the proton alignments observed in several bands at the highest spin region (rotational frequency 0.55 - 0.6 MeV). The results are interpreted within the framework of the cranked shell model (CSM). Intrinsic configurations for the new bands, up to six quasiparticles, are proposed. The co-existing coupling schemes, deformation and rotation alignment, involving identical orbitals at high spin are discussed for the high-K bands. Possible decay pathways associated with three previously proposed candidates for triaxial strongly deformed (TSD) structures in 168Hf have been investigated. The spin and excitation energy of the bandhead for the strongest band, TSD1, were determined approximately based on γ-ray coincidence relationships. Discrete links were established for the second band. The overall agreement between the observed properties of the bands and cranking calculations using the Ultimate Cranker code provides strong support for an interpretation where band TSD1 is associated with a TSD minimum, (ε2, γ) ~ (0.43, 20°), involving the π(i13/2)2 and the ν(j15/2) high-j orbitals. This constitutes the first identification of a TSD band in Hf isotopes, long-predicted by theoretical studies. The second band is understood as being associated with a near-prolate shape and a deformation enhanced with respect to the normal deformed bands. It is proposed to be built on the π(i13/2 h9/2)ν(i13/2)2 configuration. The Doppler-shift attenuation method was used to measure lifetimes of yrast states. The deformation extracted from this measurement fits well with predictions from theoretical calculations.