Triaxial Particle Rotor Model Research Articles

Chiral Doublet Bands with νh11/2 ⊗ νd−15/2 Configuration in the Particle Rotor Model

Doublet bands with νh11/2⊗νd−15/2 configuration are studied for the first time via the triaxial particle rotor model. The main properties of the doublet bands, including the energy spectra and the electromagnetic transitions, are presented for different triaxiality parameter γ. The aplanar rotation and chiral geometry are discussed based on the analysis of angular momentum components.

Properties of the 3/2−[521] band in the odd-N rare-earth nuclei

High-spin states in 161Er have been studied experimentally via the 150Nd(16O, 5n) reaction at a beam energy of 86 MeV. Three rotational bands built on the 5/2+[642], 3/2−[521], and 11/2−[505] configurations have been extended up to high-spin states, and particularly, the α = −1/2 branch of the ground state 3/2−[521] band has been revised significantly. It is found that signature inversion occurs in the 3/2−[521] band after the band crossing in 161Er. The systematics of the signature inversion associated with the 3/2−[521] configuration in the rare-earth region is discussed. The band properties are analyzed within the framework of a triaxial particle-rotor model, and a triaxial deformation is proposed to the 3/2−[521] band.

The first candidate for chiral nuclei in the [formula omitted] mass region: 80Br

Excited states of 80Br have been investigated via the 76Ge(11B, α3n) and 76Ge(7Li, 3n) reactions and a new ΔI=1 band has been identified which resides ∼ 400 keV above the yrast band. Based on the experimental results and their comparison with the triaxial particle rotor model calculated ones, a chiral character of the two bands within the πg9/2⊗νg9/2 configuration is proposed, which provides the first evidence for chirality in the A∼80 region.

Properties of the rotational bands inEr161

High-spin states in $^{161}\mathrm{Er}$ have been studied experimentally using the $^{150}\mathrm{Nd}$($^{16}\mathrm{O}$,5$\mathit{n}$) reaction at a beam energy of 86 MeV. The $5/{2}^{+}[642]$, $3/{2}^{\ensuremath{-}}[521]$, and $11/{2}^{\ensuremath{-}}[505]$ bands are extended up to high-spin states, and particularly the $\ensuremath{\alpha}=\ensuremath{-}1/2$ branch of the ground state $3/{2}^{\ensuremath{-}}[521]$ band is revised significantly. The relatively enhanced $E1$ transitions from the $3/{2}^{\ensuremath{-}}[521]$ band to the $5/{2}^{+}[642]$ band are observed. The band properties are analyzed within the framework of a triaxial particle-rotor model, and near-prolate shape and triaxial deformation are proposed to the $3/{2}^{\ensuremath{-}}[521]$ and $5/{2}^{+}[642]$ bands, respectively. Signature inversion occurs in the $3/{2}^{\ensuremath{-}}[521]$ band after the band crossing in $^{161}\mathrm{Er}$, and the systematics of the signature inversion associated with the $3/{2}^{\ensuremath{-}}[521]$ configuration are discussed. By analyzing the properties of the relatively enhanced $E1$ transitions, it is found that the $R(E1/E2)$ values show angular momentum dependence before the band crossing, and these enhanced $E1$ transitions could be attributed to octupole softness.

Chirality in odd-ARh isotopes within the triaxial particle rotor model

Adopting the fully quantal triaxial particle rotor model, the candidate chiral doublet bands in odd-$A$ nuclei $^{103}$Rh and $^{105}$Rh with $\pi g_{9/2}^{-1}\otimes\nu h^{2}_{11/2}$ configuration are studied. For the doublet bands in both nuclei, agreement is excellent for the observed energies over entire spin range and $B(M1)/B(E2)$ at higher spin range. The evolution of the chiral geometry with angular momentum is discussed in detail by the angular momentum components and their probability distributions. Chirality is found to change from chiral vibration to nearly static chirality at spin $I=37/2$ and back to another type of chiral vibration at higher spin. The influence of the triaxial deformation $\gamma$ is also studied.

Properties of the rotational bands in the transitional nucleusPt189

High-spin states in $^{189}\mathrm{Pt}$ have been studied experimentally using the $^{176}\mathrm{Yb}(^{18}\mathrm{O},5n)$ reaction at beam energies of 88 and 95 MeV. The level scheme of $^{189}\mathrm{Pt}$ has been revised significantly and extended to high-spin states. Rotational bands have been analyzed in the framework of triaxial particle-rotor model, and a $\ensuremath{\gamma}\ensuremath{\approx}\ensuremath{-}{30}^{\ifmmode^\circ\else\textdegree\fi{}}$ triaxial shape and a near-prolate shape have been proposed to the $\ensuremath{\nu}{i}_{13/2}^{\ensuremath{-}1}$ and $\ensuremath{\nu}{f}_{5/2}({p}_{3/2})$ bands, respectively. Two $\ensuremath{\Delta}I=2$ transition sequences with similar energies have been observed, and they have been proposed to be associated with the $\ensuremath{\nu}{i}_{13/2}^{\ensuremath{-}2}\ensuremath{\nu}{f}_{5/2}({p}_{3/2})$ configuration. The structure built on the $\ensuremath{\nu}{i}_{13/2}^{\ensuremath{-}2}\ensuremath{\nu}{f}_{5/2}({p}_{3/2})$ configuration could be interpreted as a pair of pseudospin partners. The level energies in the pseudospin partner bands are well reproduced by the theoretical calculations of the triaxial particle-rotor model if a near-oblate shape is assumed.

Study of the vi−113/2 band in 189Pt

High-spin levels of 189Pt have been studied with the in-beam γ-spectroscopy method via the 176Yb(18O,5n) reaction at the beam energies of 88 and 95 MeV. The previously known vi−113/2 band has been confirmed, and its unfavored signature branch extended up to the 31/2+ state. Within the framework of the triaxial particle-rotor model, the vi−113/2 band is suggested to be associated with the 11/2[615] configuration, and to have triaxial deformation.

Chiral doublet bands and energy-level crossing

Different definitions for chiral doublet bands based on excitation energies, B(E2) and B(M1) respectively are discussed in the triaxial particle rotor model. For the ideal chiral geometry, the selection rules of the electromagnetic transitions in different band definitions are illustrated. It is also shown that the energy-level crossings between chiral doublet bands may occur.

Breaking of Chiral Symmetry in 104Rh and Its NeighbouringNuclei

The possible chiral doublet structures in 104Rh with theasymmetric configuration πg9/2-1⊗νh11/2have been studied in the triaxial particle-rotor model. Thespectra, the I-ω relations and the transition probabilitiessupport the existence of the chiral bands in this nucleus. Theγ-deformation interval -35°⩽γ⩽-25° forappearance of chiral doublets in 104Rh is given. Withappropriate moment of inertia and the configuration πg9/2-1⊗νh11/2, the experimental spectra in104Rh, 106Rh, 108Rh, 110Ag have been wellreproduced by the yrast bands of the triaxial particle-rotor-modelcalculation.