Triaxial Particle Rotor Model Research Articles

Octupole correlations in stable nucleus 153Eu within reflection-asymmetric particle rotor model

Abstract The observed low-lying K=5/2± positive- and negative-parity bands in the stable nucleus 153Eu are investigated by the reflection-asymmetric triaxial particle rotor model. The experimental energy spectra, the energy staggering parameters, as well as the intraband E2 and M1 transition probabilities are well reproduced. It is found that the calculated interband B(E1) values depend sensitively on the octupole deformation parameter β30, although the energy spectra and intraband E2 and M1 transitions can be reproduced without the octupole degree of freedom. The observed enhanced E1 transition probabilities can be reproduced with β30=0.05. The detailed analysis of the intrinsic wave functions shows these nearly degenerate positive- and negative-parity bands are built on two individual proton configurations, i.e., dominated by πg9/2[Ω=5/2] and πh11/2[Ω=5/2], respectively, which differs from the parity doublet bands built on a single parity-mixed configuration.

Rotational spectroscopies of reflection-asymmetric nuclei within particle rotor model

The rotational spectroscopic properties of reflection-asymmetric nuclei investigated by the reflection-asymmetric axial or triaxial particle rotor model are briefly reviewed. The status of observations of the alternated parity bands in even–even nuclei and the parity doublet bands in odd-[Formula: see text] and odd–odd nuclei for the [Formula: see text] mass region are summarized. The reflection-asymmetric axial particle rotor model has been used to systematically describe the parity doublet bands of the odd-[Formula: see text] nuclei in this region. With the triaxial degree of freedom included, the reflection-asymmetric triaxial particle rotor model shows the ability to study the multiple chiral doublet bands with octupole correlations and explore the possible chirality-parity quartet bands.

Lifetime measurements in 80Br and a new region for observation of chiral electromagnetic selection rules

Level lifetimes for the candidate chiral doublet bands of 80Br were extracted by means of the Doppler-shift attenuation method. The absolute transition probabilities derived from the lifetimes agree well with the M1 and E2 chiral electromagnetic selection rules, and are well reproduced by the triaxial particle rotor model calculations. Such good agreements among the experimental data, selection rules of chiral doublet bands and theoretical calculations are rare and outstanding in researches of nuclear chirality. Besides odd-odd Cs isotopes, odd-odd Br isotopes in the A≈ 80 mass region represent another territory that exhibits the ideal selection rules expected for chiral doublet bands.

Interpretation of enhanced electric dipole transitions in Br73 by the reflection-asymmetric triaxial particle rotor model

The recently observed positive and negative parity bands in $^{73}\mathrm{Br}$ are investigated by the reflection-asymmetric triaxial particle rotor model. The experimental energy spectra as well as the electric transition probabilities $B(E1), B(E2)$, and the ratio $B(E1)/B(E2)$ are well reproduced by the theoretical calculations. It is found that the enhanced interband $E1$ transitions between the opposite-parity bands, a crucial evidence for octupole correlations, are mainly contributed by the intrinsic single-particle electric dipole matrix elements.

Influence of moments of inertia on transverse wobbling mode in odd-mass nuclei

The reported transverse wobbling band in odd-mass $^{105}$Pd has been reinvestigated by the triaxial particle rotor model. Employing different parameter sets of moment of inertia (MOI), several calculated results could be in good agreement with the experimental data, which show distinct modes of rotational excitation, respectively. These modes are sensitive to the ratio between the MOI at intermediate and short axis. With the increase of this ratio, a wobble about the short axis of the total angular momentum is gradually changed to a wobble about the intermediate axis. In addition, it is exhibited that precession and tunneling are two aspects of the quantum wobbling motion. The tunneling aspect dominates in the yrare states of $^{105}$Pd. The present results in $^{105}$Pd show the complexity of the transverse wobbling mode.

Evidence of octupole correlation in Se79

Two opposite parity bands I and II with eight new parity changing transitions have been identified in $^{79}\mathrm{Se}$ using the fusion-evaporation reaction $^{76}\mathrm{Ge}(^{9}\mathrm{Be}$, $\ensuremath{\alpha}2n$) at ${E}_{\mathrm{Lab}}\ensuremath{\approx}31$ MeV. The $B(M1)$ and $B(E2)$ rates of bands I and II as well as $B(E1)$ values of the linking transitions between the two bands have been determined from lifetime measurements and are compared with reflection asymmetric triaxial particle rotor model calculations. The large $B(E1)$/$B(E2)$ ratios and $B(E1)$ transition rates indicate the existence of a strong octupole correlation in the $^{79}\mathrm{Se}$ nucleus. This is also supported by the calculated potential energy surface, based on the covariant density functional theory within the three-dimensional lattice approach, which is very soft for the octupole shape degree of freedom ${\ensuremath{\beta}}_{30}$. Extracted values of the intrinsic dipole moments $|{D}_{0}|$ from the $B(E1)$ rates for the lower spin states also indicate the octupole correlation in $^{79}\mathrm{Se}$.

First observation of candidate chiral doublet bands in Z=37 Rb isotopes

High-spin states in $^{84}\mathrm{Rb}$ have been studied using the $^{76}\mathrm{Ge}(^{11}\mathrm{B}$, $3n$) reaction at a beam energy of 36 MeV. A pair of nearly degenerate positive-parity doublet bands have been extended and interpreted as candidate chiral doublet bands based on their experimental properties. This interpretation is supported by the triaxial relativistic mean-field theory and the triaxial particle-rotor model calculations. The systematic comparison of the candidate chiral bands in the $A\ensuremath{\approx}80$ mass region are also discussed. This work is the first observation of candidate chiral doublet bands in $Z=37$ Rb isotopes and extends the boundaries of the chiral nuclei in the $A\ensuremath{\approx}80$ mass region.

Parity doublet bands in Th223 within reflection-asymmetric triaxial particle rotor model

The recently updated parity doublet structures in $^{223}\mathrm{Th}$ are investigated by using the reflection-asymmetric triaxial particle rotor model. The calculated results well reproduce the available data of the energy spectra and the $B(E1)/B(E2)$ ratios for both medium spin region and the newly established higher spin region, as well as the average value of $B(M1)/B(E2)$ for spins $9/2\ensuremath{\hbar}$ and $11/2\ensuremath{\hbar}$ in the positive-parity band. The main components of the intrinsic wave functions are analyzed to investigate the intrinsic wave functions and their evolutions with spin. The parity doublet bands are mainly based on a single neutron configuration, in which the largest component of the intrinsic wave function is $\ensuremath{\nu}({g}_{9/2},{j}_{15/2})[\mathrm{\ensuremath{\Omega}}=5/2]$ and the second largest one is $\ensuremath{\nu}({g}_{9/2},{j}_{15/2})[\mathrm{\ensuremath{\Omega}}=3/2]$. The amplitude of the largest component decreases whereas the second largest one increases with increasing spin, and the signature splitting behavior for the parity doublet bands could be understood by the variation of these main components with spin.

Quadrupole and octupole collectivity in Ba143

Author(s): Morse, C; MacChiavelli, AO; Crawford, HL; Zhu, S; Wu, CY; Wang, YY; Meng, J; Back, BB; Bucher, B; Campbell, CM; Carpenter, MP; Chen, J; Clark, RM; Cromaz, M; Fallon, P; Henderson, J; Janssens, RVF; Jones, MD; Khoo, TL; Kondev, FG; Lauritsen, T; Lee, IY; Li, J; Potterveld, D; Santamaria, C; Savard, G; Seweryniak, D; Stolze, S; Weisshaar, D | Abstract: The neutron-rich barium nuclei have been the subject of intense interest due to the enhanced octupole correlations they are predicted to exhibit. The observation of enhanced octupole collectivity in Ba144,146 as measured in sub-barrier Coulomb excitation, consistent with static octupole deformation, has further heightened this interest. In the present work, these studies are extended to the neighboring odd-mass Ba143 to investigate the interplay between single-particle and collective octupole degrees of freedom. A new measurement of the first 92 - state lifetime is also presented. Reflection-Asymmetric Triaxial Particle Rotor Model calculations indicate that the negative-parity bands in Ba143 can be understood as a decoupled structure of νh9/2 parentage, while the positive-parity bands are built on a decoupled octupole phonon. No evidence for E3 excitation is observed in this work, but an upper limit is placed on the E3 matrix element to the lowest octupole band.

Selection rules of electromagnetic transitions for chirality-parity violation in atomic nuclei

The nuclear Chirality-Parity (ChP) violation, a simultaneous breaking of chiral and reflection symmetries in the intrinsic frame, is investigated with a reflection-asymmetric triaxial particle rotor model. A new symmetry for an ideal ChP violation system is found and the corresponding selection rules of the electromagnetic transitions are derived. The fingerprints for the ChP violation including the nearly degenerate quartet bands and the selection rules of the electromagnetic transitions are provided. These fingerprints are examined for ChP quartet bands by taking a two-j shell h11/2 and d5/2 with typical energy spacing for A = 130 nuclei.

Pseudospin symmetry and octupole correlations for multiple chiral doublets in Ba131

A reflection-asymmetric triaxial particle rotor model with three quasiparticles and a reflection-asymmetric triaxial rotor is developed, and applied to investigate the observed multiple chiral doublets (M\c{hi}D) candidates with octupole correlations in 131Ba, i.e., two pairs of positive-parity bands D3-D4 and D5-D6, as well as one pair of negative-parity bands D7-D8. The energy spectra, the energy staggering parameters, the B(M1)/B(E2) ratios, and the B(E1)/B(E2) ratios are reproduced well. The chiral geometries for these M\c{hi}D candidates are examined by the azimuthal plots, and the evolution of chiral geometry with spin is clearly demonstrated. The intrinsic structure for the positive-parity bands is analyzed and the possible pseudospin-chiral quartet bands are suggested.

Possible chiral doublets in 60Ni

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.

Multiple chiral doublet bands with octupole correlations in reflection-asymmetric triaxial particle rotor model

A reflection-asymmetric triaxial particle rotor model (RAT-PRM) with a quasi-proton and a quasi-neutron coupled with a reflection-asymmetric triaxial rotor is developed and applied to investigate the multiple chiral doublet (MχD) bands candidates with octupole correlations in 78Br. The calculated excited energies, energy staggering parameters, and B(M1)/B(E2) ratios are in a reasonable agreement with the data of the chiral doublet bands with positive- and negative-parity. It is found that both the triaxial deformation γ and octupole deformation β3 influence the calculated B(E1) values. The chiral geometry based on the angular momenta for the rotor, the valence proton and valence neutron is discussed in details.

Spectroscopic study of the possibly triaxial transitional nucleus 75Ge

The collective structures of Ge75 have been studied for the first time via the Ge74(α,2p1n)Ge75 fusion-evaporation reaction. Two negative-parity bands and one tentative positive-parity band built on the νp1/2,νf5/2, and νg9/2 states, respectively, are established and compared with the structures in the neighboring N=43 isotones. According to the configuration-constrained potential-energy surface calculations, a shape transition from oblate to prolate along the isotopic chain in odd-A Ge isotopes is suggested to occur at Ge75. The properties of the bands in Ge75 are analyzed in comparison with the triaxial particle rotor model calculations.Received 23 February 2017Revised 20 November 2017DOI:https://doi.org/10.1103/PhysRevC.97.034322©2018 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNuclear reactionsNuclear structure & decaysNucleon distributionProperties59 ≤ A ≤ 89Nuclear Physics

Evidence for Octupole Correlations in Multiple Chiral Doublet Bands.

Two pairs of positive-and negative-parity doublet bands together with eight strong electric dipole transitions linking their yrast positive- and negative-parity bands have been identified in ^{78}Br. They are interpreted as multiple chiral doublet bands with octupole correlations, which is supported by the microscopic multidimensionally-constrained covariant density functional theory and triaxial particle rotor model calculations. This observation reports the first example of chiral geometry in octupole soft nuclei.

Collective band structures in theTc99nucleus

Excited states in $^{99}\mathrm{Tc}$ with energies up to 6 MeV have been populated using the $^{96}\mathrm{Zr}(^{7}\mathrm{Li},\phantom{\rule{0.16em}{0ex}}4n)^{99}\mathrm{Tc}$ reaction with a laboratory beam energy of 35 MeV. Coincident $\ensuremath{\gamma}$ rays from excited nuclei produced in the reactions were detected using an array of coaxial, planar, and clover-type high-purity germanium detectors. A total of 60 new $\ensuremath{\gamma}$-ray transitions and 21 new levels are identified and placed into a new level scheme. Two collective bands assigned to be built on the $\ensuremath{\pi}{g}_{9/2}[422]5/2{}^{+}$ and $\ensuremath{\pi}{p}_{1/2}[301]1/2{}^{\ensuremath{-}}$ Nilsson configurations have been extended with spins up to 35/2 and $33/2 \ensuremath{\hbar}$, respectively. Backbending and signature inversion have been observed in the yrast band. The large signature splitting of the positive-parity band in $^{99}\mathrm{Tc}$ may be caused by a triaxial deformation, which agrees well with the electromagnetic properties, theoretical calculations based on total Routhian surface, and triaxial particle-rotor model calculations.

Collective and noncollective states in116Sb

Excited states of ${}^{116}$Sb were investigated using in-beam $\ensuremath{\gamma}$-ray spectroscopy techniques with the ${}^{114}$Cd(${}^{7}$Li, $5n$) reaction. About 25 new states and 35 new transitions were added into the level scheme of ${}^{116}$Sb. The previously known two rotational bands based on the $\ensuremath{\pi}{g}_{9/2}^{}{}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ and $\ensuremath{\pi}{g}_{9/2}^{}{}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{d}_{5/2}$ configurations have been extended up to (16)${}^{\ensuremath{-}}$ and (13)${}^{+}$ states, respectively. A new $\ensuremath{\Delta}I=1$ band was identified, and interpreted in terms of the triaxial particle rotor model calculations.

Description of the candidate chiral doublet bands in 98Tc

The candidate chiral doublet bands in 98Tc with configuration πg9/2 ⊗ νh11/2 are studied theoretically 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.

The Influence of Triaxiality Parameter γ on the Chiral Doublet Bands with (πg9/2)−1 (νh11/2)2 Configuration

The chiral doublet bands with three-quasiparticle configuration (πg9/2)−1 (νh11/2)2 are studied by the fully quantal triaxial particle rotor model. The energy spectra and B(M1)/B(E2) ratios of the doublet bands with different triaxiality parameter γ are systematically analyzed. It is found that γ is a sensitive parameter for the properties of these doublet bands.

Shape Co-Existence in the Transitional Nuclide 157Yb

High-spin states in 157Yb have been populated in the 144Sm(16O, 3n)157Yb fusion-evaporation reaction at a beam energy of 85 MeV, and two rotational bands have been established for the first time. Within the framework of the triaxial particle-rotor model, the energy spectra and single-particle configurations of 157Yb are investigated. The calculated energy spectra agree well with the experimental data. The newly observed νf7/2 band, and the previously known νi13/2 band in 157Yb, are also discussed by means of Total-Routhian-Surface methods. The structural characters observed in 157Yb provide evidence for the shape coexistence of three distinct shapes: prolate, triaxial and oblate. At higher spins, both the νf7/2 band and the νi13/2 band in 157Yb undergo a shape evolution with sizable alignments occurring.