Systematics of K-pi=8(-) isomers in N=74 nuclei

An isomer with a half-life of 6+/-1 mu s has been observed in the N=74 nucleus Gd-138, populated following the reaction Cd-106(Cl-35,p2n)Gd-138. Th, isomer decays via a 583 keV EI transition with a hindrance per degree of K forbiddenness, f(v)=24. This value is similar to the values measured for the N=74 isotones Nd-134 and Sm-136 but markedly different from that measured for Ba-130. This suggests that there is some change in structure across the N=74 isotones and possible explanations of this feature are discussed

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

Persistence of K isomerism in the N=104 isotones: Observation of a high-seniority isomer in Re-179(75)

The nuclear decay of Re-179(75) has been studied following the Ho-165(O-18,4n)Re-179 and Yb-173(B-11,5n)Re-179 reactions. Previously unobserved multiquasiparticle states have been identified in Re-179(75), with highly K-forbidden decays. One of these, with a half-life of 466+/-15 mus, 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

Multi-quasiparticle isomers and rotationnal bands in 178^{178}W

The high spin structure of the nucleus W has been studied following the Er(C,5n) reaction. Many previously unidentified rotational bands are seen based on high-K, 2-, 4-, 6-and 8-quasiparticle structures, some of which are isomeric. The excitation energies of the multi-quasiparticle bandheads are compared with BCS calculations, including residual interactions. The bands show substantial increases in moments-of-inertia with increasing quasiparticle number. These are examined in terms of pairing blocking. The effect of blocked pairing is also taken into account in the calculation of g-factors, which supports the configuration assignments. The K=25, 8-quasiparticle band forms the yrast line from its bandhead upwards. This bandhead is a 220 ns isomer whose decay is strongly hindered, compared to the decay of the four- and six-quasiparticle structures

Tilted Rotation and Backbending in an odd-proton Nucleus

Tilted-axis rotation, arising from Fermi-aligned configurations, has been observed for the first time to cause backbending in an odd-proton nucleus. In 181Re, two t-bands are found to be energetically favored relative to the usual rotation-aligned s-bands, presenting an alternative form of cold nuclear rotation. Interactions between the bands are weak, and unambiguous comparisons with tilted-axis-cranking calculations can be made.</p