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The potential presence of wobbling motions in even-even nuclei 112Ru, 114Pd, 150Nd, and 188Os are explored by the five-dimensional collective Hamiltonian based on the relativistic density functional theory (5DCH-RDFT). The theoretical results successfully reproduce experimental energy spectra and electromagnetic transition probabilities. Analyses of the potential energy surfaces and probability density distributions in the (β,γ) deformation plane as well as the quadrupole asymmetry parameter 〈cos⁡3δ〉 reveal that 150Nd shows near-axial symmetry in contrast to the triaxial deformation in 112Ru, 114Pd, and 188Os. Additionally, spin coherent state (SCS) map is introduced for the first time to the 5DCH framework to visualize the geometry of angular momentum. It is revealed that the wobbling mode, characterized by oscillations of total angular momentum J about the medium axis, is present in 112Ru but absent in 150Nd.

Two new negative-parity bands have been identified in the odd-odd 104Rh nucleus. According to their experimentally observed properties, they have the same π(1g9/2)−1⊗ν(1h11/2)1 high-j configuration as the previously known negative-parity chiral doublet bands. This observation raises the possibility of the existence of multiple chiral doublet bands, MχD, in this nucleus. Comparing the properties of the observed bands with results of detailed theoretical calculations, one can conclude that the lower energy parts of bands 1 and 2 are chiral partner bands with the π(1g9/2)−1⊗ν(1h11/2)1 two-quasiparticle configuration, while bands 3 and 4 are chiral partner bands with the π(1g9/2)−1⊗ν(1g7/2)−2(1h11/2)1 four-quasiparticle configuration. Thus, MχD based on different configurations is observed in 104Rh.

The critical spin Ic (or critical frequency ħωc) represents the minimum spin (or rotational frequency) required for stable chiral solutions in nuclear systems. The effect of pairing on the critical spin has been examined for the particle-hole configuration π(1h11/2)⊗ν(1h11/2)−1 with a triaxial deformation parameter of γ=30∘ using the particle rotor model, which treats the total angular momentum as a good quantum number. Increasing pairing interaction keeps the critical spin Ic constant, but decreases the critical rotational frequency ħωc. This is due to that the enhanced pairing interaction causes valence nucleons angular momenta to align preferentially along the medium axis, resulting in a larger effective collective moment of inertia and facilitating the emergence of chiral rotation at a lower frequency. However, even with an increase in pairing gap from 0.0 to 2.0MeV, the resulting increase in medium axis alignment is less than 1ħ, which is insufficient to change the value of the critical spin Ic. This study suggests that the critical spin remains robust against the influence of pairing interaction.

Two nearly degenerate positive-parity bands with the πg9/22⊗νg9/2−1 configuration and three nearly degenerate negative-parity bands with the πg9/2(p3/2,f5/2)⊗νg9/2−1 configuration have been identified in 81Kr. They are interpreted as chiral doublet bands and pseudospin-chiral triplet bands, which is supported by the constrained covariant density functional theory and the multiparticle plus rotor model calculations. The present work reports two new chiral configurations πg9/22⊗νg9/2−1 and πg9/2(p3/2,f5/2)⊗νg9/2−1, and the first example of pseudospin-chiral triplet bands involving the π(p3/2,f5/2) pseudospin doublet.

Several new bands have been identified in 130Ba, among which there is one with band-head spin 8+. Its properties are in agreement with the Fermi-aligned νh11/22, 7/2−[523]⊗9/2−[514] Nilsson configuration. This is the first observation of a two-quasiparticle t-band in the A=130 mass region. The t-band is fed by a dipole band involving two additional h11/2 protons. The odd-spin partners of the proton and neutron S-bands and the ground-state band at high spins are also newly identified. The observed bands are discussed using several theoretical models, total Routhians surfaces (TRS), tilted axis cranking (TAC), particle rotor model (PRM) and projected shell model (PSM), which strongly suggest the coexistence of prolate and oblate shapes polarized by rotation aligned two-proton and two-neutron configurations, as well as prolate collective rotations around axes with different orientations. With the new results, 130Ba presents one of the best and most complete sets of collective excitations that a γ-soft nucleus can manifest at medium and high spins, revealing a diversity of shapes and rotations for the nuclei in the A=130 mass region. Keywords: Nuclear structure, Collective rotations, Shape coexistence, Particle rotor model, Projected shell model, Tiltid axis cranking

The open problem on whether or not the chirality exists in doublet bands M1 and M4 in light-mass even-even nucleus 60Ni is studied by adopting the recently developed fully quantal four-j shells triaxial particle rotor model. The corresponding experimental energy spectra, energy differences between doublet bands, and the available B(M1)/B(E2) values are successfully reproduced. The analyses on the basis of the angular momentum components, the azimuthal plots, and the K-plots suggest that the chiral modes exist at I≥12ħ in doublet bands M1 and M4.

The second-phonon (nω=2) wobbling band has been established in the nucleus 135Pr. Conclusive evidence for its wobbling nature comes from the ΔI=1, E2 character of the transitions between the new band and the previously identified transverse wobbler band (nω=1) in this nucleus. Theoretical calculations in the framework of the quasiparticle triaxial rotor and triaxial projected shell models are found to be in good agreement with the experimental results.

The three-dimensional tilted axis cranking covariant density functional theory (3D-TAC CDFT) is used to study the chiral modes in 135Nd. By modeling the motion of the nucleus in rotating mean field as the interplay between the single-particle motions of several valence particle(s) and hole(s) and the collective motion of a core-like part, a classical Routhian is extracted. This classical Routhian gives qualitative agreement with the 3D-TAC CDFT result for the critical frequency corresponding to the transition from planar to aplanar rotation. Based on this investigation a possible understanding of tilted rotation appearing in a microscopic theory is provided.

The yrast lines in Kr isotopes with N=42, 44, and 46 are investigated in a beyond mean field framework with both prolate-oblate coexistence and quasiparticle alignment taken into account. Quasiparticle orbitals with high-j and low-Ω on the oblate side are shown to be responsible for the sharp backbending observed in 82Kr, by driving the yrast shape from prolate to oblate. This suggests that quasiparticle alignment may not be neglected in the investigation of the shape evolution along the yrast line.

The static quadrupole moments (SQMs) of nuclear chiral doublet bands are investigated for the first time taking the particle-hole configuration π(1h11/2)⊗ν(1h11/2)−1 with triaxial deformation parameters in the range 260∘≤γ≤270∘ as examples. The behavior of the SQM as a function of spin I is illustrated and analyzed. It is found that in the region of chiral vibrations the SQMs of doublet bands are strongly varying with I, whereas in the region of static chirality the SQMs of doublet bands are almost constant. Hence, the measurement of SQMs provides a new criterion for distinguishing the modes of nuclear chirality. Moreover, in the high-spin region the SQMs can be approximated by an analytic formula with a proportionality to cos⁡γ for both doublet bands. This provides a way to extract experimentally the triaxial deformation parameter γ for chiral bands from the measured SQMs.

The g-factor and static quadrupole moment for the wobbling mode in the nuclide 133La are investigated as functions of the spin I by employing the particle rotor model. The model can reproduce the available experimental data of the g-factor and static quadrupole moment. The properties of the g-factor and static quadrupole moment as functions of I are interpreted by analyzing the angular momentum geometry of the collective rotor, proton-particle, and total nuclear system. It is demonstrated that the experimental value of the g-factor at the bandhead of the yrast band leads to the conclusion that the rotor angular momentum is R≃2. Furthermore, the variation of the g-factor with the spin I yields the information that the angular momenta of the proton-particle and total nuclear system are oriented parallel to each other. The negative values of the static quadrupole moment over the entire spin region are caused by an alignment of the total angular momentum mainly along the short axis. Differences of the static quadrupole moment between the wobbling and yrast band originate from a wobbling excitation with respect to the short axis.

The chirality suggested for the doublet bands B2 and B2a in 195Tl in A∼190 region is reexamined. The potential-energy curves and the configurations together with the deformation parameters are obtained by the constrained covariant density functional theory. The corresponding experimental energy spectra, energy differences between doublet bands, and the available B(M1)/B(E2) values are investigated by the fully quantal particle rotor model. Analysis on the basis of the angular momentum components, the K-plots, and the azimuthal plots suggest a planar rotation interpretation for the bands B2 and B2a. Hence, it coexists with the aplanar rotation in the other doublet bands B4 and B4a in 195Tl.

A particle rotor model, which couples nucleons in four single-j shells to a triaxial rotor core, is developed to investigate the five pairs of nearly degenerate doublet bands recently reported in the even-even nucleus 136Nd. The experimental energy spectra and available B(M1)/B(E2) values are successfully reproduced. The angular momentum geometries of the valence nucleons and the core support the chiral rotation interpretations not only for the previously reported chiral doublet, but also for the other four candidates. Hence, 136Nd is the first even-even candidate nucleus in which the multiple chiral doublets exist. Five pairs of chiral doublet bands in a single nucleus is also a new record in the study of nuclear chirality.

β-decay studies of neutron-rich nuclei in and around the “island of inversion” have been performed. With a systematic investigation of half-lives for the isotonic chains from N=19 to 22, conspicuous kinks observed at Z=13 provide a clear signature of a boundary on the northern (high-Z) side of the island. Based on the comparison with shell model calculations using Gogny D1S and SDPF-M interactions, a newly determined 22+ state in 34Si at 4519 keV presents an experimental evidence of triaxiality in this region and sheds more light on the structure of the transition across the northern boundary of the island.

The heavy ion fusion–evaporation reaction study for the high-spin spectroscopy of 75As has been performed via the reaction channel 70Zn(9Be, 1p3n)75As at a beam energy of 42 MeV. The collective structure especially a dipole band in 75As is established for the first time. The properties of this dipole band are investigated in terms of the self-consistent tilted axis cranking covariant density functional theory. Based on the theoretical description and the examination of the angular momentum components, this dipole band can be interpreted as a novel stapler band, where the valence neutrons in (1g9/2) orbital rather than the collective core are responsible for the closing of the stapler of angular momentum.