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Register a new userQuasiparticle and $gamma$-band structures in $^{156}$Dy
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Excited band structures recently observed in $^{156}$Dy are investigated using the microscopic triaxial projected shell model (TPSM) approach and the quasiparticle random phase approximation (QRPA) based on the rotating mean-field. It is demonstrated that new observed excited bands, tracking the ground-state band, are the $gamma$-bands based on the excited two-quasineutron configurations as conjectured in the experimental work.
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The rotational bands in the neutron-rich nuclei $^{153-157}$Pm are investigated by a particle-number conserving method. The kinematic moments of inertia for the 1-quasiparticle bands in odd-$A$ Pm isotopes $^{153, 155, 157}$Pm are reproduced quite well by the present calculation. By comparison between the experimental and calculated moments of inertia for the three 2-quasiparticle bands in the odd-odd nuclei $^{154, 156}$Pm, their configurations and bandhead spins have been assigned properly. For the 2-quasiparticle band in $^{154}$Pm, the configuration is assigned as $pi5/2^-[532]otimes u3/2^-[521]$ ($K^pi=4^+$) with the bandhead spin $I_0=4hbar$. In $^{156}$Pm, the same configuration and bandhead spin assignments have been made for the 2-quasiparticle band with lower excitation energy. The configuration $pi5/2^+[413]otimes u5/2^+[642]$ ($K^pi=5^+$) with the bandhead spin $I_0=5hbar$ is assigned for that with higher excitation energy.
Evidence of strong coupling of quasiparticle excitations with gamma-vibration is shown to occur in transitional nuclei. High-spin band structures in [166,168,170,172]Er are studied by employing the recently developed multi-quasiparticle triaxial projected shell model approach. It is demonstrated that a low-lying K=3 band observed in these nuclei, the nature of which has remained unresolved, originates from the angular-momentum projection of triaxially deformed two-quasiparticle (qp) configurations. Further, it is predicted that the structure of this band depends critically on the shell filling: in [166]Er the lowest K=3 2-qp band is formed from proton configuration, in [168]Er the K=3 neutron and proton 2-qp bands are almost degenerate, and for [170]Er and [172]Er the neutron K=3 2-qp band becomes favored and can cross the gamma-vibrational band at high rotational frequencies. We consider that these are few examples in even-even nuclei, where the three basic modes of rotational, vibrational, and quasi-particle excitations co-exist close to the yrast line.
The basis space in the triaxial projected shell model (TPSM) approach is generalized for odd-odd nuclei to include two-neutron and two-proton configurations on the basic one-neutron coupled to one-proton quasiparticle state. The generalization allows to investigate odd-odd nuclei beyond the band crossing region and as a first application of this development, high-spin band structures recently observed in odd-odd $^{194-200}$Tl isotopes are investigated. In some of these isotopes, the doublet band structures observed after the band crossing have been conjectured to arise from the spontaneous breaking of the chiral symmetry. The driving configuration of the chiral symmetry in these odd-odd isotopes is one-proton and three-neutrons rather than the basic one-proton and one-neutron as already observed in many other nuclei. It is demonstrated using the TPSM approach that energy differences of the doublet bands in $^{194}$Tl and $^{198}$Tl are, indeed, small. However, the differences in the calculated transition probabilities are somewhat larger than what is expected in the chiral symmetry limit. Experimental data on the transition probabilities is needed to shed light on the chiral nature of the doublet bands.
In the present work, the basis space in the triaxial projected shell model approach is expanded to include three and five quasiparticle configurations for odd-proton systems. This extension allows to investigate the high-spin band structures observed in odd-proton systems up to and including the second band crossing region, and as a first major application of this development, the high-spin properties are investigated for odd-mass $^{125-137}$Pr and $^{127-139}$Pm isotopes. It is shown that band crossings in the studied isotopes have mixed structures with first crossing dominated by one-proton coupled to two-neutron configuration for the lighter isotopes which then changes to three-proton configuration with increasing neutron number. Further, $gamma$-bands based on quasiparticle states are also delineated in the present work, and it is predicted that these band structures built on three-quasiparticle configurations become favoured in energy for heavier systems in the high-spin region.
We discuss in depth the application of the classical concepts for interpreting the quantal results from the triaxial rotor core without and with odd-particle. The corresponding limitations caused by the discreteness and finiteness of the angular momentum Hilbert space and the extraction of the relevant features from the complex wave function and distributions of various angular momentum components are discussed in detail. New methods based on spin coherent states and spin squeezed states are introduced. It is demonstrated that the spin coherent state map is a powerful tool to visualize the angular momentum geometry of rotating nuclei. The topological nature of the concepts of transverse and longitudinal wobbling is clarified and the transitional axis-flipregime is analysed for the first time.
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