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.

Electromagnetic transitions in multiple chiral doublet bands

Multiple chiral doublet bands （MχD） in the 80, 130 and 190 mass regions are studied by the model of γ=90°triaxial rotor coupled with identical symmetric proton-neutron configurations. By selecting a suitable basis, the calculated wave functions are explicitly exhibited to be symmetric under the operator A, which is defined as rotation by 90° about the 3-axis with the exchange of valance proton and neutron. We found that both M1 and E2 transitions are allowed between levels with different values of A, while they are forbidden between levels with same values of A. Such a selection rule holds true for MχD in different mass regions.

Doublet bands at borders of A ≈ 130 island of chiral candidates: Case study of 120I

Positive-parity doublet bands were reported in 120I.Based on these,we discuss the corresponding experimental characteristics,including rotational alignment,and re-examine the corresponding configuration assignment.The self-consistent tilted axis cranking relativistic mean-field calculations indicate that the doublet bands are built on the configurationπh11/2νh11/2^-1.By adopting the two quasiparticles coupled with a triaxial rotor model,the excitation energies,energy staggering parameter S(I),B(M1)/B(E2),effective angles,and K plots are discussed and compared with available data.The obtained results support the interpretation of chiral doublet bands for the positive-parity doublet bands in 120I,and hence identify this nucleus as the border of the A≈130 island of chiral candidates.

πg_(9/2)νh_(11/2) doublet bands in A～100 mass region

Using the model with one particle and one hole coupled with a triaxial rotor, the πg9/2/1/2νh11/2 doublet bands in the A～100 mass region are studied, and compared with the πg9/2/1/2νh11/2 doublet bands. It is found that the calculated results for the configuration of πg9/2/1/2νh11/2 are very similar the results for a pure h11/2 proton particle and a neutron quasiparticle with λn = ε5. After including the pair correlation, the model describes the candidate chiral doublet bands in 106Rh successfully, which supports the interpretation of chirality geometry.

Description of the candidate chiral doublet bands in ^(98)Tc

The candidate chiral doublet bands in 98 Tc with configuration πg9/2νh11/2 are studied the- oretically for the first time via the triaxial particle rotor model. The main properties of the doublet bands including the energy spectra and electromagnetic transitions are calculated for different triaxiality parameter γ, and the data in 98Tc can be well described by the calculations with γ = 38°. Based on the analysis of angular momentum components, it is found that the chiral rotational geometry in 98Tc deviates from the ideal chiral picture.

Chiral geometry in multiple chiral doublet bands

The chiral geometry of multiple chiral doublet bands with identical configuration is discussed for different triaxial deformation parameters γ in the particle rotor model with πh11/2×γh11/2^-1.The energy spectra,electromagnetic transition probabilities B（M1） and B（E2）,angular momenta,and K-distributions are studied.It is demonstrated that the chirality still remains not only in the yrast and yrare bands,but also in the two higher excited bands whenγ deviates from 30°.The chiral geometry relies significantly on γ,and the chiral geometry of the two higher excited partner bands is not as good as that of the yrast and yrare doublet bands.