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We investigate the influence of deformation on the possible occurrence of long-lived K isomers in Hf isotopes around N = 116, using configuration-constrained calculations of potential-energy surfaces. Despite having reduced shape elongation, the multiquasiparticle states in 186,188Hf remain moderately robust against triaxial distortion, supporting the long expected occurrence of exceptionally long-lived isomers. The calculations are compared with available experimental data. [ABSTRACT FROM AUTHOR]

The spectroscopy of 73Ge has been investigated via the 70Zn(7Li,3np) 73Ge fusion-evaporation reaction. A previously known band built on the v(f5/2) orbital is extended up to higher-spin states and a new rotational band built on the v(g9/2) orbital is established. The observed band crossing and shape evolution induced by the alignment in 73Ge are studied in comparison with the similar structures in the neighboring N = 41 isotones and the cranked Woods-Saxon-Strutinsky calculations by means of total-Routhian-surface (TRS) methods. The inversion of the order of the g9/2 neutron and the g9/2 proton crossing frequency observed in the negative-parity v(f5/2) bands between 73Ge and 75Se, 77Kr can be ascribed to their different triaxial deformations. At higher spins, both the v(f5/2) and v(g9/2) bands in 73Ge undergo a shape evolution with sizable alignments occurring. The characters of large signature splitting in v(g9/2) band of 73Ge are discussed. [ABSTRACT FROM AUTHOR]

The neutron-rich nucleus n2Rh has been reinvestigated by examining the prompt γ rays emitted in the spontaneous fission of 252Cf with the Gammasphere detector array. A new side band was built in 112Rh. Total Routhian surface calculations have been performed and confirm the role of triaxiality in the negative-parity structure of 112Rh. [ABSTRACT FROM AUTHOR]

The spectroscopy of 157Yb has been studied via 144Sm(16O,3n)157Yb fusion-evaporation reaction. The properties of bands associated with the νi13/2 orbital and νh9/2 orbital in 157Yb are analyzed in comparison with the triaxial particle-rotor-model calculations. The characters of signature splitting for both positive-parity νi13/2 and negative-parity νh9/2 bands in 157Yb and heavier odd-A Yb isotopes are discussed. The newly observed bands 1 and 2 in 157Yb are suggested to be the signature partners of the νh9/2 band. A systematic study of the band crossing frequencies associated with the i13/2 neutron-pair and h11/2 proton-pair alignments for the Yb isotopes, as well as the Er and Hf isotopes, are made. [ABSTRACT FROM AUTHOR]

The neutron-rich nuclei 109Pd and 111Pd were produced as fission fragments following the 30Si + l68Er reaction at 142 MeV. Using the identification based on the coincidences with the complementary fission fragments, the only positive-parity bands observed so far in l09Pd and 111Pd emerged from this work. A band, built on top of the 5/2+ ground state exhibiting Δ = 1 energy-level staggering, was observed in each of these nuclei. Both nuclei of interest, 109Pd and 111Pd, are suggested to lie in the transitional region of Pd isotopes of maximum y softness. The ground states of both nuclei are predicted by total Routhian surface calculations to be extremely y soft with shallow triaxial minima. The first crossing in the new bands is proposed to be attributable to an alignment of h²11/2 neutrons. [ABSTRACT FROM AUTHOR]

In-beam γ spectroscopy of the stable nucleus 127I has been studied experimentally using the 124Sn(7Li, 4nγ)127I reaction at a beam energy of 32 MeV. The high-spin level scheme of 127I is extended significantly. Negative-parity levels built on the 11/2-, πh11/2 particle state are observed up to (35/2-) and described as a decoupled band, extending our knowledge of decoupled structures to the most neutron-rich stable iodine isotope. Two ΔI = 2 yrast positive-parity sequences are proposed to be associated with the πg7/2 configuration due to observations of several strong interband transitions, and two weakly populated ΔI =2 positive-parity bands are newly identified and interpreted as arising mainly from the πd5/2 configuration. Three-quasiparticle configurations are assigned to the Iπ = 15/2+ and 23/2+ states according to the existing knowledge in neighboring nuclei; irregular noncollective and regular collective excitations built on these two (15/2+ and 23/2+) states are observed to coexist at similar energies. The observed three-quasiparticle band structures are further interpreted with the aid of configuration-constrained potential energy surface calculations. [ABSTRACT FROM AUTHOR]

Excited states in 55V and 55Cr have been populated via pn and 2n evaporation channels, respectively, following the fusion of a 48Ca beam at 172 MeV with a 9Be target. Level schemes have been deduced for the two nuclides to excitation energies of 7467 (55V) and 12226 keV (55Cr), with spins of 27/2+ and 33/2+, respectively. Negative-parity states are compared with shell-model calculations using three different effective interactions in the full fp model space. Negative-parity levels of 55Cr are explained in terms of single-particle fp-shell configurations outside N = 28 and N = 32 cores. Positive-parity states in both isotopes show evidence for the involvement of neutron g9/2 configurations. In the case of 55Cr, a quasirotational structure based on the 1/2+[440] Nilsson orbital is observed up to the terminating state. In 55V, positive-parity states do not exhibit well-developed collective features, and the observation of octupole decays is an indication of their importance in transitions from neutron g9/2 configurations to the fp shell. Experimental results are compared with the predictions of a traditional shell model, the projected shell model, and total-Routhian-surface calculations. [ABSTRACT FROM AUTHOR]

The density-dependent finite-range Gogny force has been used to derive the effective Hamiltonian for the shell-model calculations of nuclei. The density dependence simulates an equivalent three-body force, while the finite range gives a Gaussian distribution of the interaction in the momentum space and hence leads to an automatic smooth decoupling between low-momentum and high-momentum components of the interaction, which is important for finite-space shell-model calculations. Two-body interaction matrix elements, single-particle energies, and the core energy of the shell model can be determined by the unified Gogny force. The analytical form of the Gogny force is advantageous to treat cross-shell cases, while it is difficult to determine the cross-shell matrix elements and single-particle energies using an empirical Hamiltonian by fitting experimental data with a large number of matrix elements. In this paper, we have applied the Gogny-force effective shell-model Hamiltonian to the p- and sd-shell nuclei. The results show good agreements with experimental data and other calculations using empirical Hamiltonians. The experimentally known neutron drip line of oxygen isotopes and the ground states of typical nuclei 10B and 18N can be reproduced, in which the role of three-body force is non-negligible. The Gogny-force-derived effective Hamiltonian has also been applied to the cross-shell calculations of the sd-pf shell. [ABSTRACT FROM AUTHOR]

Neutron-rich 107Mo has been reinvestigated by analyzing the large statistics γ-γ-γ and γ-γ-γ-γ coincidence data from the spontaneous fission of 252Cf at the Gammasphere detector array. Two new bands have been identified. The potential-energy surface calculations of this nucleus have been performed. The calculations show evidence for the 5/2+[413] configuration of the ground-state band and 7/2-[523] configuration for the 348-keV excited band, as assigned in previous work. The two bands newly established are proposed to be one- and two-phonon γ-vibrational bands built on the 7/2-[523] Nilsson orbital, respectively, in the current paper. Triaxial projected shell-model (TPSM) calculations have been performed to explain the level structure and are found in fair agreement with experimental data. In particular, the TPSM study confirms the γ- and γγ-vibrational structure for the two observed excited band structures. Systematics of the one- and two-phonon γ-vibrational bands in the A~100 Mo series is also discussed. [ABSTRACT FROM AUTHOR]

High-spin-level schemes of 118,119Ag are established for the first time by analyzing the high statistics γ-γ-γ and γ-γ-γ-γ coincidence data from the spontaneous fission of 252Cf at Gammasphere. Two bands with 12 new levels in 118Ag and three bands with 14 new levels in 119Ag have been identified. A total Routhian surface calculation and projected shell model calculation have been performed to understand the behavior of these two nuclei. The calculations indicate oblate shape in 118,119Ag. [ABSTRACT FROM AUTHOR]

High-spin band structures of 200Tl have been studied by γ-ray spectroscopic methods using the 198Pt(7Li,5n)200Tl reaction at 45 MeV of beam energy. The level scheme of 200Tl has been extended significantly and several new band structures have been established with the observation of 60 new transitions. The πh9/2⊗νi13/2 oblate band has been extended beyond the particle alignment frequencies. The band structures and the other excited states have been compared with the neighboring odd-odd Tl isotopes. Total Routhian surface calculations have been performed to study the deformation and shape changes as a function of spin in this nucleus. These calculations could reproduce the particle alignment frequency and suggest that the neutron pair alignment in νi13/2 orbital induces γ softness in 200Tl. [ABSTRACT FROM AUTHOR]