Signature Splitting Research Articles

Prediction of novel effects in rotational nuclei at high speed

The study of high-speed rotating matter is a crucial research topic in physics due to the emergence of novel phenomena. In this letter, we combined cranking covariant density functional theory (CDFT) with a similarity renormalization group approach to decompose the Hamiltonian from the cranking CDFT into different Hermite components, including the non-relativistic term, the dynamical term, the spin-orbit coupling, and the Darwin term. Especially, we obtained the rotational term, the term relating to Zeeman-like effect, and the spin-rotation coupling due to consideration of rotation and spatial component of vector potential. By exploring these operators, we aim to identify novel phenomena that may occur in rotating nuclei. Signature splitting, Zeeman-like effect, and spin-rotation coupling are among the potential novelties that may arise in rotating nuclei. Additionally, we investigated the observability of these phenomena and their dependence on various factors such as nuclear deformation, rotational angular velocity, and magnetic field-like strength.

An improved microscopic core–quasiparticle coupling model for spectroscopy of odd-mass nuclei with octupole correlations

The microscopic core–quasiparticle coupling model for odd-A nuclei with octupole correlations is extended to include the monopole, quadrupole and octupole couplings between the core and the odd nucleon, based on the framework of covariant density functional theory. The model is tested in a study of low-lying excitation spectra for the odd-A nucleus [Formula: see text]Ra. Theoretical results, e.g., the parity doublets, interband [Formula: see text] and intraband [Formula: see text], are in very good agreement with the available data. In particular, the description of signature splitting in the ground-state band has been improved. This method provides a very useful tool for a systematic study of low-energy spectra in odd-mass actinides with octupole correlations.

νi13/2 structures in Sm155 and Gd159 : Supporting evidence of a Z=60 deformed subshell gap

Maximal ground-state deformation should occur when both proton and neutron Fermi surfaces are located at midshell. However, subshell gaps that stabilize large deformation can exist at proton or neutron values other than midshell. One such gap may occur at $Z=60$ in the rare-earth region, as the energy of the first ${2}^{+}$ states in even-even nuclei are often lowest in an isotonic chain for neodymium ($Z=60$) rather than the midshell isotopes of dysprosium ($Z=66$). Further evidence of this deformed gap has now been observed by investigating the signature splitting systematics of the $\ensuremath{\nu}{i}_{13/2}$ bands found in the odd-$N$, rare-earth nuclei. These were aided by the present observation of the $\ensuremath{\nu}{i}_{13/2}$ band in $^{159}\mathrm{Gd}$ and the confirmation of the same structure in $^{155}\mathrm{Sm}$ via the transfer of a neutron from a $^{160}\mathrm{Gd}$ beam to a $^{154}\mathrm{Sm}$ target.

Signature splitting of the g7/2[404]7/2+ bands in Ba131 and Ce133

Excited states in Ba131 and Ce133 were studied using in-beam γ-ray spectroscopy through the Sn122(C13,4n)Ba131 and Te125(C12,4n)Ce133 reactions, respectively. A strongly coupled band, associated with the νg7/2[404]7/2+ configuration, was identified in Ba131 and Ce133. It is the first time to observe the νg7/2[404]7/2+ bands in the N=75 isotones. The signature partners exhibit considerable energy splitting in comparison with those in the πg7/2[404]7/2+ bands in the odd-A Ta and Re isotopes. Extensive cranked shell model and quasiparticle-plus-triaxial-rotor model calculations reveal the origin of the signature splitting, which depends not only on the triaxiality, but also on the configuration mixing with nearby low-j orbitals.3 MoreReceived 30 July 2021Revised 13 October 2021Accepted 19 November 2021DOI:https://doi.org/10.1103/PhysRevC.104.064304©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective levelsElectromagnetic transitionsNuclear structure & decaysTransfer reactionsProperties90 ≤ A ≤ 149Nuclear Physics

Lifetime measurements and evidence for triaxial nuclear shapes in Cs127

Rotational bands built on single quasiproton excitations in $^{127}\mathrm{Cs}$ have been investigated using the $^{121}\mathrm{Sb}(^{12}\mathrm{C},\ensuremath{\alpha}2n$) reaction and the ROSPHERE detector array at IFIN-HH, Bucharest. The lifetimes in the yrast negative-parity band based on the proton in ${h}_{11/2}$ orbital have been measured by applying the Doppler-shift attenuation method. The lifetime of the ${7/2}^{+}$ 273-keV state, member of the rotational band associated with the proton ${g}_{7/2}$ orbital, has been determined as $\ensuremath{\tau}$ = 1.22(5) ns by the fast timing technique. The experimental data were compared with the calculations performed using the quasiparticle plus triaxial rotor model and deformation parameters ${\ensuremath{\epsilon}}_{2}$ and $\ensuremath{\gamma}$ have been derived for the positive- and negative-parity structures. Evidence for triaxial nuclear shapes in the states described by the proton ${h}_{11/2}$ orbital was provided by both signature splitting and $B(E2,\mathrm{\ensuremath{\Delta}}J=2)$ transition strengths.

Possible magnetic rotational bands in 84Rb

High-spin states in 84Rb are studied by using the 70Zn(18O, p3n)84Rb reaction at a beam energy of 75 MeV. Three high-lying negative-parity bands are established, whose level spacings are very regular, i.e., there is no signature splitting. The dipole character of the transitions of these three bands is assigned by the γ-γ directional correlations of oriented states (DCO) intensity ratios and the multipolarity M1 is suggested by analogy with multiparticle excitations in neighboring nuclei. Strong M1 and weak or no E2 transitions are observed. All these characteristic features show they are magnetic rotational bands.

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.

Lifetime measurement in picoseconds for the excited states of 129Cs

The high-spin states of 129Cs were populated using the fusion-evaporation reaction 124Sn(11B, 6n)129Cs. We have studied the nuclear structure properties – signature splitting and reduced transition probabilities (B(E2)) – of many excited states in 129Cs. Lifetimes in picoseconds were measured using the Doppler Shift Attenuation Method (DSAM). We employed two gating procedures, Gating on transition above (GTA) and Gating on transition below (GTB), to obtain the experimental results consistently. We carefully analyzed the data by incorporating the effects related to nuclear reaction, e.g., change in the velocity and cross section of residues when moving in a medium. Theoretical investigations were carried out for two yrast bands – a positive-parity based on πg7/2, and another negative-parity based on πh11/2 – using the single quasi-particle rotor model (PRM). For both bands, we found the same deformation parameter values ϵ≃0.14, |γ|=18∘ (Lund convention) by simultaneously matching the experimental and theoretical results for the signature splitting and B(E2) values. Most of our results are new and reasonably well understood theoretically.

Erratum: Signature splitting inversion and backbending in Rb80 [Phys. Rev. C 87 , 034320 (2013)

Erratum: Signature splitting inversion and backbending in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Rb</mml:mi><mml:mprescripts/><mml:none/><mml:mn>80</mml:mn></mml:mmultiscripts></mml:math> [Phys. Rev. C <b>87</b> , 034320 (2013)

Evolution of intrinsic nuclear structure in medium mass even-even Xenon isotopes from a microscopic perspective * * Arun Bharti acknowledges the financial support from the Science and Engineering Research Board, under the project file no. CRG/2019/001231 and Ridham Bakshi acknowledges the financial support from The Department of Science and Technology, Government of India, INSPIRE Fellowship under sanction no. DST/INSPIRE Fellowship/2018/IF180368

In this study, the multi-quasiparticle triaxial projected shell model (TPSM) is applied to investigate -vibrational bands in transitional nuclei of . We report that each triaxial intrinsic state has a -band built on it. The TPSM approach is evaluated by the comparison of TPSM results with available experimental data, which shows a satisfactory agreement. The energy ratios, B(E2) transition rates, and signature splitting of the -vibrational band are calculated.

Revealing multiple band structures in Xe131 from α -induced reactions

The excited states in the transitional nucleus $^{131}\mathrm{Xe}$ have been populated by using $\ensuremath{\alpha}$-induced fusion-evaporation reaction and the de-exciting $\ensuremath{\gamma}$ rays were detected with the Compton suppressed clover detector setup of the Indian National Gamma Array coupled to digital data acquisition system. The existing level structure of $^{131}\mathrm{Xe}$ has been significantly extended with the observation and placement of 72 new $\ensuremath{\gamma}$-ray transitions. The use of light-ion ($\ensuremath{\alpha}$) beam helped to identify several new band structures in $^{131}\mathrm{Xe}$ with different quasiparticle (qp) configurations. The multipolarities of the observed $\ensuremath{\gamma}$ rays have been determined on the basis of the directional correlation from oriented states ratio and polarization asymmetry measurements. The yrast negative-parity band has been confirmed up to ${35/2}^{\ensuremath{-}}$ spin and the highly nonyrast signature partner of this band has been identified for the first time. The positive-parity band, based on the ${3/2}^{+}$ ground state, has been extended up to ${23/2}^{+}$ with the observation of a signature inversion, which signifies a pair of particle alignment around the spin of 15/2 $\ensuremath{\hbar}$. A dipole band, consisting of $M1$ transitions has been identified and assigned a 5-qp configuration. A new band structure built on a 3-qp ${23/2}^{+}$ state has been observed with a large signature splitting. A comparison in the isotopic and isotonic chains reveals the transitional nature of the $N=77$ nuclei. Total Routhian surface calculations have been performed to understand the structure of $^{131}\mathrm{Xe}$ associated with different configurations.

Microscopic study of ground state bands in N = 45 and 46 isotones in mass region A ∼ 70–80

Using the angular-momentum projected quasiparticle states and a simple quadrupole–quadrupole + monopole–pairing + quadrupole-pairing type Hamiltonian, Projected Shell Model calculations have been performed to study the nuclear structure properties of some N = 45, 46 isotones in the mass region A = 70–80. The results are obtained for the yrast energy spectrum, rotational alignments, back-bending and reduced transition probabilities [B(M1) and B(E2)]. Results of our calculations exhibit satisfactory agreement with experimental data. Signature splitting and signature inversion which are the characteristics of this mass region have also been reproduced and discussed for these nuclei.

Signature splitting in the positive parity bands of $$^{{127}}\hbox {Xe}$$

Signature splitting in the positive parity bands of $$^{{127}}\hbox {Xe}$$

Observation of signature partner bands in Sb117

Rotational band structures and low-lying single-particle levels in $^{117}\mathrm{Sb}$ have been populated using reaction $^{115}\mathrm{In}(\ensuremath{\alpha}$, $2n)^{117}\mathrm{Sb}$ at a beam energy of 28 MeV and investigated using $\ensuremath{\gamma}$-ray spectroscopic techniques. The existing level scheme has been extended with the observation of 31 new transitions. The signature partner of the band structure based on the configuration of $\ensuremath{\pi}{g}_{7/2}\phantom{\rule{4pt}{0ex}}\ensuremath{\bigotimes}\phantom{\rule{4pt}{0ex}}2\mathrm{p}\text{\ensuremath{-}}2\mathrm{h}$ of the $^{116}\mathrm{Sn}$ core has been established in $^{117}\mathrm{Sb}$ for the first time. Several single-particle nonyrast transitions connecting to various band structures have also been identified. Measurements of the DCO ratios, polarization asymmetry and angular distribution of the observed $\ensuremath{\gamma}$ rays have been carried out to assign the spin-parities to the levels of all the band structures and the low-lying single-particle states, populated in the present work. The spin-parities are also determined for the states of the two previously unassigned bands. The lower-spin structures have been interpreted on the basis of large-scale shell-model calculations using OXBASH. Particle Rotor Model (PRM) calculations have been carried out to explain the large signature splitting of the observed signature partner bands.

Intermediate structure and dipole bands in the transitional Ba134 nucleus

The intermediate and high-spin states of the $^{134}\mathrm{Ba}$ nucleus have been investigated up to spin ${I}^{\ensuremath{\pi}}=({20}^{\ensuremath{-}})$ using the $^{124}\mathrm{Sn}(^{13}\mathrm{C}, 3n)^{134}\mathrm{Ba}$ reaction at a beam energy of 48 MeV. The ${R}_{\mathrm{DCO}}$ and polarization asymmetry measurements were carried out to assign the spin and parity of the levels. Three ($\mathrm{\ensuremath{\Delta}}I=2$) negative parity bands were studied above the 1985.9 keV level having spin ${I}^{\ensuremath{\pi}}={5}^{\ensuremath{-}}$. The two quasiparticle $\ensuremath{\nu}[{h}_{11/2}\ensuremath{\bigotimes}({s}_{1/2}/{d}_{3/2})]$ configuration has been assigned to these bands based on the systematics of the $\mathrm{Ba}$ (even-$N$) isotopes and similarity in the behavior of signature splitting and $B(M1)/B(E2)$ ratios. Further, two ($\mathrm{\ensuremath{\Delta}}I=1$) dipole bands have also been observed starting at the 5677.9 and 5284.5 keV levels with spin ${I}^{\ensuremath{\pi}}={14}^{\ensuremath{-}}$ and ${15}^{+}$, respectively. The configuration of these bands was suggested from the systematics of the similar structure in the neighboring nuclei. Tilted axis cranking (TAC) calculations were carried out using the four quasiparticle $\ensuremath{\pi}[{h}_{11/2}({g}_{7/2}/{d}_{5/2})]\ensuremath{\bigotimes}\ensuremath{\nu}{[{h}_{11/2}]}^{2}$ and $\ensuremath{\pi}[{h}_{11/2}({g}_{7/2}/{d}_{5/2})]\phantom{\rule{4pt}{0ex}}\ensuremath{\bigotimes}\phantom{\rule{4pt}{0ex}}\ensuremath{\nu}[{h}_{11/2}{d}_{3/2}]$ configurations for bands D1 and D2, respectively. The TAC calculations and systematic studies of similar structures in the neighboring $N=78$ isotones suggest that the dipole band (D1) observed at 5677.9 keV level may have the magnetic rotation character.

Investigation of signature inversion in I126 through lifetime measurements

The reduced transition probabilities $B(E2)$ and $B(M1)$ of the negative-parity yrast states of $^{126}\mathrm{I}$ were studied by measuring the lifetimes in picoseconds using the Doppler-shift attenuation method. We investigated the phenomena of signature splitting and inversion using the two quasiparticle-plus triaxial rotor model (PRM). The experimental result---a sharp decrease in the $B(E2)$ values at the signature inversion---indicated a shape change with a possible shift in the axis of rotation. We interpreted this observation as a change in the triaxiality parameter, with values $\ensuremath{\gamma}=\ensuremath{-}{10}^{\ensuremath{\circ}}$ (Lund convention) below the inversion and $\ensuremath{\gamma}={25}^{\ensuremath{\circ}}$ above it and a constant value of axial deformation of $\ensuremath{\beta}\ensuremath{\approx}0.15$. We also assigned the valence particle configuration---neutron in the ${h}_{11/2}$ orbital and proton predominantly in the ${d}_{5/2}$ orbital mixed with the ${g}_{7/2}$ orbital---from the PRM calculation. Furthermore, the calculation reproduced the overall observed behavior of the signature splitting and inversion reasonably well. The observed backbending at the rotational frequency of 0.47 MeV was due to neutron alignment consistent with the second band crossing from the quasiparticle Routhian diagram.

Low-lying positive parity bands in 162Yb

The structure of the low-lying positive parity bands in 162Yb has been studied at iThemba LABS, using the 150Sm(16O,4n)162Yb fusion-evaporation reaction. A band built on the first excited $0^{+}_{2}$ state has been identified for the first time. In addition, we report new rotational levels that form the band structures of both the odd and even spin components of the $\gamma$ -vibrational band. The first excited $0^{+}_{2}$ band and the even spin members of the $\gamma$ -vibrational band exhibit a Landau-Zenner crossing. This crossing demonstrates that the significant signature splitting between the odd and even spin members of the $\gamma$ band is contributed to by band mixing.

High-spin level structure and Ground-state phase transition in the odd-mass 103−109Rh isotopes in the framework of exactly solvable sdg interacting boson–fermion model

In this article, the negative-parity states in the odd-mass Rh103−109 isotopes in terms of the sd and sdg interacting-boson fermion models were studied. The transitional interacting boson–fermion model Hamiltonians in sd and sdg-IBFM versions based on affine SU(1,1) Lie Algebra were employed to describe the evolution from the spherical to deformed gamma unstable shapes along with the chain of Rh isotopes. In this method, sdg-IBFM Hamiltonian, which is a three level pairing Hamiltonian was determined easily via the exactly solvable method. Some observables of the shape phase transitions such as energy levels, the two neutron separation energies, signature splitting of the γ-vibrational band, the α-decay and double β−-decay energies were calculated and examined for these isotopes. The present calculation correctly reproduces the spherical to gamma-soft phase transition in the Rh isotopes. Some comparisons were made with sd-IBFM.

Investigation of triaxiality in 54122–128Xe isotopes in the framework of sdg-IBM

In this paper, a transitional interacting boson model (IBM) Hamiltonian in both sd-(IBM) and sdg-IBM versions based on affine [Formula: see text] Lie algebra is employed to describe deviations from the gamma-unstable nature of Hamiltonian along the chain of Xe isotopes. sdg-IBM Hamiltonian proposed a better interpretation of this deviation which cannot be explained in the [Formula: see text]-boson models. The nuclei studied have well-known [Formula: see text] bands close to the [Formula: see text]-unstable limit. The energy levels, [Formula: see text] transition rates and signature splitting of the [Formula: see text] -vibrational band are calculated via the affine SU(1,1) Lie algebra. An acceptable degree of agreement was achieved based on this procedure. It is shown that in these isotopes the signature splitting is better reproduced by the inclusion of sdg-IBM. In none of them, any evidence for a stable, triaxial ground state shape is found.

Rotational structure of odd-proton 103, 105, 107, 109, 111Tc isotopes

A systematic study of the yrast band structure for the neutron-rich odd-mass 103-111Tc nuclei is carried out using Projected Shell Model. The rotational band structure has been studied up to a maximum spin of $ 59/2^{+}$ . Excellent agreement with available experimental data for all isotopes is obtained. The energy spectra and electromagnetic transition strengths in terms of the configuration mixing of the angular-momentum projected multi-quasiparticle states are studied in detail. Signature splitting in the yrast rotational band is well described in the perspective of nuclear structure physics. The back-bending phenomenon is also well described for these nuclei in the present work.