Second Backbend in the Mass A ~ 180 Region

Within the framework of selfconsistent cranked Hartree-Fock- Bogoliubov theory(one-dimensional) we predict second backbend in the yrast line of Os-182 at $I \approx 40$, which is even sharper than the first one observed experimentally at $I \approx 14$. Around such a high spin the structure becomes multi-quasiparticle type, but the main source of this strong discontinuity is a sudden large alignment of i_13/2 proton orbitals along the rotation axis followed soon by the alignment of j_15/2 neutron orbitals. This leads to drastic structural changes at such high spins. When experimentally confirmed, this will be observed for the first time in this mass region, and will be at the highest spin so far.Comment: 13 pages, 4 ps figure

Rotation of an eight-quasiparticle isomer

A T-1/2 = 220 ns, eight-quasiparticle isomer, with four unpaired neutrons and four unpaired protons, has been established at an excitation energy of 6576 keV in the prolate deformed nucleus, W-178. The associated rotational band has also been identified, revealing the collective properties in the presence of blocked pairing correlations, with expected quenching of the nuclear superfluidity. The band retains a small degree of rotational alignment, and has a less-than-rigid dynamic moment of inertia

Multi-quasiparticle isomers and rotational bands in 181Re

High-spin states in 181 Re have been populated using the 176 Yb( 11 B, 6n) reaction and their decays studied using the CAESAR γ -ray spectrometer. Thirteen bands of rotational states have been observed based on 1-, 3- and 5-quasiparticle structures, inc

Structure and decay of a four-quasiparticle 15(-) isomer in Ta-180

A four quasiparticle high-K isomer with a meanlife of 45(2) mu s has been identified at 1451 keV in Ta-180, populated in the Yb-176(B-11,alpha 3n) Ta-180 reaction. The isomer decays into a rotational band which is associated with the two-quasiparticle 9(-) isomer at 75.3 keV. Analysis of the branching ratios within that band and the magnetic moment for the 9(-) isomer, supports the configuration assignment to the 9(-) isomer. The K hindrance for the E2 decay of the 15(-) isomer to the 9(-) band is substantially lower than that for an apparently similar 15(-) isomer in Ta-178, a difference which can be attributed partly to a change from the pi 9/2(-)[514]nu(3)9/2(+) [624]7/2(-)[514]5/2(-)[512] configuration in Ta-178 to the pi(3)9/2(-)[514]7/2(+)[404]5/2(+)[402]nu 9/2(+)[624] configuration in Ta-180. The reduced hindrance factors for E2 decays from related four-quasiparticle isomers in the isotopes Ta-176,Ta-178,Ta-180 match the hindrances of the corresponding E2 decays from component 6(+) core states in the hafnium isotopes, Hf-174,Hf-176,Hf-178

Persistence of K isomerism in the N = 104 isotones: Observation of a high-seniority isomer in 75179Re

The nuclear decay of Re has been studied following the Ho(O,4n)Re and Yb(B,5n)Re reactions. Previously unobserved multiquasiparticle states have been identified in Re, with highly K-forbidden decays. One of these, with a half-life of 466±15 μs, is the longest-lived high-seniority (>6) isomer yet discovered. This metastable state offers an opportunity to explore K isomerism as protons are added away from the midshell region. In addition, the excitation energies of several previously "floating" bands have been determined. Energies, lifetimes, configuration assignments, and g factors are discussed and compared to predictions of blocked BCS calculations

Rotational and multi-quasiparticle excitations in 183Re

The high-spin structure of the nucleus 183Re has been studied following the 176Yb(11B,4n) reaction. High-K, multi-quasiparticle excitations compete with collective rotation in the formation of the yrast and near-yrast structures. Broken-pair (i13/2)2 excitations (t-bands) play a dominant role, generating considerable angular momentum both along and perpendicular to the prolate symmetry axis. The stability of axially symmetric, prolate shapes is explored through comparisons with potential-energy-surface calculations. The possible onset of oblate rotation at high angular momentum is discussed