Search

High-spin states in W174 (Z = 74) have been populated using the reaction Te128(Ti50, 4n)W174 at beam energies of 215 and 225 MeV. The Gammasphere array was used to detect the γ rays emitted by the evaporation residues. Four previously known collective band structures have been extended, and 16 new rotational sequences observed. Two are built upon isomeric states, one corresponding to a two-quasiparticle K = 8 isomer, the other to a four-quasiparticle K = 12 isomer, with the latter exhibiting strong K-violating ΔK=12 decays to the ground state band. Nucleonic configurations for the two- and four-quasiparticle excitations are proposed, and Woods-Saxon cranking calculations are presented to understand the rotational structures. Decay mechanisms of multi-quasiparticle K isomers are discussed in terms of the prevalent phenomenological models, with special emphasis on γ-tunneling calculations. Surprisingly, the latter underpredict the decay hindrance for the K = 12 isomer by three orders of magnitude, unlike all other isomer decays in this mass region.

High spin states in 237Np and 241Am have been studied with the "unsafe" Coulomb excitation technique. In each nucleus, signature partner rotational bands built on the [523]5/2- and [642]5/2+ orbitals of respective h9/2 and i13/2 parentage have been delineated. An additional pair of bands based on the [521]3/2- (f7/2) state was also observed in 241Am. New information on the even-even 236Pu and 242Cm transfer products is also presented. From the present data, the role of i13/2 protons in generating angular momentum in the even-even nuclei of the region is documented. A satisfactory description of the evolution of the rotational sequences with spin is achieved within the framework of the cranked shell model. Nevertheless, when combined with information on odd-neutron nuclei available from elsewhere, the data highlight significant shortcomings of the available theoretical predictions.

In a series of measurements with Gammasphere, striking differences were found between the yrast and negative parity bands in 238-240Pu and those in 241-244Pu. These differences can be linked to variations with mass of the strength of octupole correlations. At the highest spins, 238-240Pu are found to exhibit properties associated with stable octupole deformation, suggesting that a transition with spin from a vibration to stable deformation may have occurred.