Collective Oblate Rotation at High Spins in Neutron-RichHf180

Abstract

We report on experimental evidence for collective oblate rotation becoming favored at high spins in a rigid, well-deformed, axially symmetric nucleus. Excited states established up to spin 20variant Planck's over 2pi in 180Hf are consistent with predictions that nucleon alignments would favor oblate over prolate shapes at high spins in neutron-rich Hf isotopes. The results highlight the influence of valence orbitals on the interplay between nucleon alignments and nuclear shapes and provide a rare example of independent particle dynamics in competing potential wells.

Isomers and oblate rotation in Pt isotopes: Delineating the limit for collectivity at high spins

“…This is understood in terms of the higher moments-of-inertia usually associated with prolate states [1] which, in turn, result in the lowering of their excitation energy with respect to that of all other levels. Nevertheless, in the A ≈ 180-190 region, collective oblate states have been predicted [2] and observed [3][4][5][6][7] at high spin. Here rotation alignment, a process by which pairs of nucleons decouple under the stress of the Coriolis force and align their spin with the rotation axis, favors the occupation of specific orbitals driving the nuclei * Corresponding author at: UM-DAE Centre for Excellence in Basic Sciences, Mumbai 400098, India.…”

Isomers and oblate collectivity at high spin in neutron-rich Pt isotopes

“…Since low-Ω orbitals typically exhibit a higher degree of alignment compared to high-Ω ones over a similar range of rotational frequency, oblate states are found to be lower in energy than the corresponding prolate ones. While this phenomenon was first predicted quite some time ago [2], as yet, there are a relatively small number of nuclei where collective oblate rotation is experimentally observed to the favored excitation mode [3][4][5]. Oblate shapes are expected to be more favored in neutron-rich nuclei however these are experimentally difficult to explore.…”

Decoupled and semi-decoupled bands in Hg197 and Hg199

“…Nuclei in the A = 190-200 region exhibit several interesting aspects of structure. In the Hf-Os (Z = 72-76) region, pronounced prolate deformation is evident near the ground state with a transition to oblate shapes at high spin around neutron number N = 108-110 [1,2]. Pt (Z = 78) isotopes exhibit triaxial shapes at low spin [3,4] while Hg (Z = 80) nuclei are characterized by oblate deformation [5][6][7][8][9] with Pb (Z = 82) isotopes being near-spherical.…”

“…Statistical uncertainties on γ-ray intensities and DCO ratios are listed. + → 29/2 + 0.79(2) 354.0 100.0(21) 653.0 17/2 + → 13/2 + − E γ (keV) I γ E i (keV) I π i → I π…”