arXiv subjects

S. Q. Zhang

Publications and source records attributed to S. Q. Zhang.

At least 55 records · Page 3Linked to original sources

arXiv2011

The first candidate for chiral nuclei in the $A\sim80$ mass region: $^{80}$Br

Excited states of $^{80}$Br have been investigated via the $^{76}$Ge($^{11}$B, $α$3n) and $^{76}$Ge($^{7}$Li, 3n) reactions and a new $ΔI$ = 1 band has been identified which resides $\sim$ 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 $πg_{9/2}\otimes νg_{9/2}$ configuration is proposed, which provides the first evidence for chirality in the $A\sim80$ region.

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arXiv2011

Novel structure for magnetic rotation bands in 60Ni

The self-consistent tilted axis cranking relativistic mean-field theory based on a point-coupling interaction has been established and applied to investigate systematically the newly observed shears bands in 60Ni. The tilted angles, deformation parameters, energy spectra, and reduced M1 and $E2$ transition probabilities have been studied in a fully microscopic and self-consistent way for various configurations and rotational frequencies. It is found the competition between the configurations and the transitions from the magnetic to the electric rotations have to be considered in order to reproduce the energy spectra as well as the band crossing phenomena. The tendency of the experimental electromagnetic transition ratios B(M1)/B(E2) is in a good agreement with the data, in particular, the B(M1) values decrease with increasing spin as expected for the shears mechanism, whose characteristics are discussed in detail by investigating the various contributions to the total angular momentum as well.

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arXiv2011

Multiple chiral doublet candidate nucleus $^{105}$Rh in a relativistic mean-field approach

Following the reports of two pairs of chiral doublet bands observed in $^{105}$Rh, the adiabatic and configuration-fixed constrained triaxial relativistic mean-field (RMF) calculations are performed to investigate their triaxial deformations with the corresponding configuration and the possible multiple chiral doublet (M$χ$D) phenomenon. The existence of M$χ$D phenomenon in $^{105}$Rh is highly expected.

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arXiv2011

Chirality in odd-$A$ Rh isotopes within 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 $πg_{9/2}^{-1}\otimesνh^{2}_{11/2}$ 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 $γ$ is also studied.

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arXiv2010

Chiral geometry of higher excited bands in triaxial nuclei with particle-hole configuration

The lowest six rotational bands have been studied in the particle-rotor model with the particle-hole configuration $πh^1_{11/2}\otimesνh^{-1}_{11/2}$ and different triaxiality parameter $γ$. Both constant and spin-dependent variable moments of inertial (CMI and VMI) are introduced. The energy spectra, electromagnetic transition probabilities, angular momentum components and $K$-distribution have been examined. It is shown that, besides the band 1 and band 2, the predicted band 3 and band 4 in the calculations of both CMI and VMI for atomic nuclei with $γ=30^\circ$ could be interpreted as chiral doublet bands.

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arXiv2010

Octupole deformation for Ba isotopes in a reflection-asymmetric relativistic mean-field approach

The potential energy surfaces of even-even $^{142-156}$Ba are investigated in the constrained reflection-asymmetric relativistic mean-field approach with parameter set PK1. It is shown that for the ground states, $^{142}$Ba is near spherical,$^{156}$Ba well quadrupole-deformed, and in between $^{144-154}$Ba octupole deformed. In particular, the nuclei $^{148,150}$Ba with $N=92,94$ have the largest octupole deformations. By including the octupole degree of freedom, energy gaps $N=88$, $N=94$ and $Z=56$ near Fermi surfaces for the single-particle levels in $^{148}$Ba with $β_2\sim 0.26$ and $β_3\sim 0.17$ are found. Furthermore, the performance of the octupole deformation driving pairs ($ν2f_{7/2}$, $ν1i_{13/2}$) and ($π2d_{5/2}$, $π1h_{11/2}$) is demonstrated by analyzing the single-particle levels near Fermi surfaces in $^{148}$Ba.

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arXiv2010

Octupole degree of freedom for the critical-point candidate nucleus $^{152}$Sm in a reflection-asymmetric relativistic mean-field approach

The potential energy surfaces of even-even $^{146-156}$Sm are investigated in the constrained reflection-asymmetric relativistic mean-field approach with parameter set PK1. It is shown that the critical-point candidate nucleus $^{152}$Sm marks the shape/phase transition not only from U(5) to SU(3) symmetry, but also from the octupole-deformed ground state in $^{150}$Sm to the quadrupole-deformed ground state in $^{154}$Sm. By including the octupole degree of freedom, an energy gap near the Fermi surface for single-particle levels in $^{152}$Sm with $β_2 = 0.14 \sim 0.26$ is found, and the important role of the octupole deformation driving pair $ν2f_{7/2}$ and $ν1i_{13/2}$ is demonstrated.

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arXiv2010

Open Problems in Understanding the Nuclear Chirality

Open problems in the interpretation of the observed pair of near degenerate $ΔI = 1$ bands with the same parity as the chiral doublet bands are discussed. The ambiguities for the existing fingerprints of the chirality in atomic nuclei and problems in existing theory are discussed, including the description of quantum tunneling in the mean field approximation as well as the deformation, core polarization and configuration of particle rotor model (PRM). Future developments of the theoretical approach are prospected.

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arXiv2009

Candidate MKiD nucleus 106Rh in triaxial relativistic mean-field approach with time-odd fields

The configuration-fixed constrained triaxial relativistic mean-field approach is extended by including time-odd fields and applied to study the candidate multiple chiral doublets (MKiD) nucleus 106Rh. The energy contribution from time-odd fields and microscopical evaluation of center-of-mass correction as well as the modification of triaxial deformation parameters beta, gamma due to the time-odd fields are investigated. The contributions of the time-odd fields to the total energy are 0.1-0.3 MeV and they modify slightly the gamma values. However, the previously predicted multiple chiral doublets still exist.

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arXiv2008

Chirality in odd-$A$ nucleus $^{135}$Nd in particle rotor model

A particle rotor model is developed which couples several valence protons and neutrons to a rigid triaxial rotor core. It is applied to investigating the chirality in odd-$A$ nucleus $^{135}$Nd with $πh_{11/2}^2\otimesνh^{-1}_{11/2}$ configuration for the first time in a fully quantal approach. For the two chiral sister bands, the observed energies and the $B(M1)$ and $B(E2)$ values for the in-band as well as interband transitions are reproduced excellently. Root mean square values of the angular momentum components and their probability distributions are used for discussing in detail the chiral geometry of the aplanar rotation and its evolution with angular momentum. Chirality is found to change from a soft chiral vibration to nearly static chirality at spin $I=39/2$ and back to another type of chiral vibration at higher spin.

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arXiv2008

Electromagnetic Dipole Strength in Transitional Nuclei

Electromagnetic dipole absorption cross-sections of transitional nuclei with large-amplitude shape fluctuations are calculated in a microscopic way by introducing the concept of Instantaneous Shape Sampling. The concept bases on the slow shape dynamics as compared to the fast dipole vibrations. The elctromagnetic dipole strength is calculated by means of RPA for the instantaneous shapes, the probability of which is obtained by means of IBA. Very good agreement with the experimental absorption cross sections near the nucleon emission threshold is obtained.

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arXiv2008

Signature splitting in $^{173}$W with triaxial particle rotor model

A particle rotor model with a quasi-neutron coupled with a triaxially deformed rotor is applied to study signature splitting for bands with intruder orbital $\nu7/2^{+} [633]$ and non-intruder orbital $\nu5/2^{-}[512]$ in $^{173}$W. Excellent agreement with the observed energy spectra has been achieved for both bands. Signature splitting for band $\nu7/2^{+} [633]$, and band $\nu5/2^{-}[512]$ before the onset of signature inversion, is satisfactorily reproduced by introducing the $γ$ degree of freedom. The phase and amplitude of signature splitting in band $\nu5/2^{-}[512]$ is attributed to strong competition between $2f_{7/2}$ and $1h_{9/2}$ components. However, the explanation of signature inversion in band $\nu5/2^{-}[512]$ self-consistently is beyond the present one quasi-neutron coupled with a triaxially deformed rotor.

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arXiv2007

Chiral bands for quasi-proton and quasi-neutron coupling with a triaxial rotor

A particle rotor model (PRM) with a quasi-proton and a quasi-neutron coupled with a triaxial rotor is developed and applied to study chiral doublet bands with configurations of a $h_{11/2}$ proton and a $h_{11/2}$ quasi-neutron. With pairing treated by the BCS approximation, the present quasi-particle PRM is aimed at simulating one proton and many neutron holes coupled with a triaxial rotor. After a detailed analysis of the angular momentum orientations, energy separation between the partner bands, and behavior of electromagnetic transitions, for the first time we find aplanar rotation or equivalently chiral geometry beyond the usual one proton and one neutron hole coupled with a triaxial rotor.

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arXiv2007

Examining the chiral geometry in 104Rh and 106Rh

The criteria for chiral doublet bands based on one particle and one hole coupled to a triaxial rotor have been summarized. Two representative cases in $A\sim100$ odd-odd nuclei, nearly degenerate $ΔI =1$ doublet bands in $^{104}$Rh and $^{106}$Rh are checked against these chiral criteria. It is shown that $^{106}$Rh possesses better chiral geometry than $^{104}$Rh, although the energy near degeneracy is achieved in $^{104}$Rh in comparison with the constant energy separation of doublet bands in $^{106}$Rh.

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arXiv2007

Doublet bands in $^{126}$Cs in the triaxial rotor model coupled with two quasiparticles

The positive parity doublet bands based on the $πh_{11/2}\otimesνh_{11/2}$ configuration in $^{126}$Cs have been investigated in the two quasi-particles coupled with a triaxial rotor model. The energy spectra $E(I)$, energy staggering parameter $S(I)=[E(I)-E(I-1)]/2I$, $B(M1)$ and $B(E2)$ values, intraband $B(M1)/B(E2)$ ratios, $B(M1)_{\textrm{in}}/B(M1)_{\textrm{out}}$ ratios, and orientation of the angular momentum for the rotor as well as the valence proton and neutron are calculated. After including the pairing correlation, good agreement has been obtained between the calculated results and the data available, which supports the interpretation of this positive parity doublet bands as chiral bands.

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arXiv2006

Giant halo in relativistic and non-relativistic approaches

The phenomena of giant halo and halo of neutron-rich even-Ca isotopes are investigated and compared in the framework of the relativistic continuum Hartree-Bogoliubov (RCHB) and non-relativistic Skyrme Hartree-Fock-Bogoliubov (HFB) calculations. With two parameter sets for each of the RCHB and the Skyrme HFB calculations, it is found that although halo phenomena exist for Ca isotopes near neutron drip line in both calculations, the halo of the Skyrme HFB calculations starts at a more neutron-rich nucleus than that of the RCHB calculations, and the RCHB calculations have larger neutron root-mean-square (rms) radii systematically in N >= 40 than those of the Skyrme HFB calculations. The former difference comes from difference in shell structure. The reasons for the latter can be partly explained by the neutron 3s1/2 orbit, which causes more than 50% of the difference among the four calculations for neutron rms radii at 66Ca.

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arXiv2005

Multi chiral-doublets in one single nucleus

Adiabatic and configuration-fixed constraint triaxial relativistic mean field (RMF) approaches are developed for the first time and a new phenomenon, the existence of multi chiral-doublets (M$χ$D), i.e., more than one pairs of chiral doublets bands in one single nucleus, is suggested for nuclei in A~100 region, typically for $^{106}$Rh, based on the triaxial deformations together with their corresponding proton and neutron configurations.

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arXiv2005

Shell-model-Like APproach (SLAP) for the nuclear properties in relativistic mean field theory

A Shell-model-Like APproach (SLAP) suggested to treat the pairing correlations in relativistic mean field theory is introduced, in which the occupancies thus obtained having been iterated back into the densities. The formalism and numerical techniques are given in detail. As examples, the ground state properties and low-lying excited states for Ne isotopes are studied. The results thus obtained are compared with the data available. The binding energies, the odd-even staggering, as well as the tendency for the change of the shapes in Ne isotopes are correctly reproduced.

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