No abstract

An isomer with a half-life of 6Ϯ1 s has been observed in the Nϭ74 nucleus 138 Gd, populated following the reaction 106 Cd( 35 Cl,p2n) 138 Gd. The isomer decays via a 583 keV E1 transition with a hindrance per degree of K forbiddenness, f ϭ24. This value is similar to the values measured for the Nϭ74 isotones 134 Nd and 136 Sm but markedly different from that measured for 130 Ba. This suggests that there is some change in structure across the Nϭ74 isotones and possible explanations of this feature are discussed.

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A T]/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. 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.

The nuclear decay of 75 179 Re has been studied following the 165 Ho( 18 O,4n) 179 Re and 173 Yb( 11 B,5n) 179 Re reactions. Previously unobserved multiquasiparticle states have been identified in 75 179 Re, with highly K-forbidden decays. One of these, with a half-life of 466Ϯ15 s, is the longest-lived high-seniority ͑Ͼ6͒ 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.