Negative-parity Bands Research Articles

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.

Evidence for octupole collectivity in ^{172}{mathrm {Pt}}

Excited states in the extremely neutron-deficient nucleus ^{172}{mathrm {Pt}} were populated via ^{96}mathrm {Ru}(^{78}mathrm {Kr},2p) and ^{92}mathrm {Mo}(^{83}mathrm {Kr},3n) reactions. The level scheme has been extended up to an excitation energy of approx 5~hbox {MeV} and tentative spin-parity assignments up to I^pi = 18^+. Linear polarization and angular distribution measurements were used to determine the electromagnetic E1 character of the dipole transitions connecting the positive-parity ground-state band with an excited side-band, firmly establishing it as a negative-parity band. The lowest member of this negative-parity structure was firmly assigned spin-parity 3^-. In addition, we observed an E3 transition from this 3^- state to the ground state, providing direct evidence for octupole collectivity in ^{172}{mathrm {Pt}}. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the 3^- state as a collective octupole-vibrational state.

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.

"Beat" Patterns of Odd-Even Staggering in Octupole Bands of Light Actinides

The Δ I = 1 staggering (odd-even staggering) in octupole bands of light actinides. is found to exhibit a "beat" behaviour as a function of the angular momentum J, forcing us to revise the traditional belief that this staggering decreases gradually to, zero and then remains at this zero value. Various algebraic models (spf-Interacting Boson Model, spdf-IBM, Vector Boson Model, Nuclear Vibron Model) predict in their su(3) limits constant staggering for this case, being thus unable to describe the "beat" behaviour. An explanation of the "beat" behaviour is given in terms of two Dunham expansions (expansions in terms of powers of I ( I + 1) ) with slightly different sets of coefficients for the ground state band and the negative parity band, the difference in the values of the coefficients being attributed to Coriolis couplings to other negative parity bands.

High spin structure of 155Dy

High spin states in 155Dy have been studied by γ-γ coincidence measurements via the 124Sn(36S, 5n)155Dy reaction at a beam energy of 155 MeV. Eight rotational bands have been populated and observed up to high spin (I<91/2).The band features have been analysed within the framework of the cranked shell model. The Ì13/2 neutron alignments and the h11/2 proton alignments are discussed. B(M1)/B(E2) ratios have also been extracted for the strongly coupled bands to deduce further information on the detailed structure of these bands. For the highest states (above spin 30) of the negative parity bands an irregularity in y-ray energies appears which is discussed in terms of band termination.

Properties of some Nuclei with Mass Number A=140

The positive ground-state band (GSB) of isobars was calculated using the Bohr – Mottelson (BM) model, interacting vector boson model (IVBM), and interacting boson model (IBM-1), while the negative-parity band (NPB) of was calculated using the BM model and IVBM. To determine the properties of the ground-state band, the back-bending curve, the E-GOS curve (Eγ/I), the ratio (r(I +2)/I) and the staggering have been plotted as a function of the spin (I). The contour plots show that all nuclei under consideration have complicate properties.

Band structures in 169Tm and the structures of Tm isotopes around N = 98

The excited states of 169Tm have been studied via the 169Tm(32S,32S′)169Tm* reaction at the beam energy of 164MeV. The $\gamma$-rays were detected using the Indian National Gamma Array (INGA) setup, composed of 19 Compton-suppressed clover HPGe detectors. A new level scheme of 169Tm with 11 newly placed $ \gamma$-rays has been proposed. A band crossing in the $ \pi [541]1/2^{-}$ band and several interband E1 transitions between this and the $ \pi [411]1/2^{+}$ ground-state band have been observed for the first time in this nucleus. The role of the $N=98$ deformed shell gap has been discussed by comparing the band crossing parameters of the negative parity bands in Tm and other neighboring nuclei. The origin of the interband E1 transitions has been investigated in terms of coupling to octupole degrees of freedom. The shape evolution of the Tm isotopes around $ N=98$ have been studied in the projected and cranked shell model approaches, both of which predict a change in shape from an axial prolate to a triaxial one after band crossing in these nuclei. The new data and the calculations help to understand the unusual structural phenomena reported for the nuclei with $ N=98$.

Chirality of Nd135 reexamined: Evidence for multiple chiral doublet bands

One new pair of positive-parity chiral doublet bands have been identified in the odd-A nucleus Nd135 which together with the previously reported negative-parity chiral doublet bands constitute a third case of multiple chiral doublet (MχD) bands in the A≈130 mass region. The properties of the MχD bands are well reproduced by constrained covariant density functional theory and particle rotor model calculations. The newly observed MχD bands in Nd135 represents an important milestone in supporting the existence of MχD in nuclei.Received 6 April 2019Revised 23 May 2019DOI:https://doi.org/10.1103/PhysRevC.100.024314©2019 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective levelsCollective modelsElectromagnetic transitionsNuclear spin & parityNuclear structure & decaysNuclear Physics

Analysis of states in 13C and their cluster structure

Accurate studies on 13C spectroscopy have great impact in the present understanding of the role played by extra-neutrons in stabilizing α-cluster structures formed in light nuclei. Carbon-13 is in fact the simplest systems that can be formed by adding a neutron to make a triple-α molecular-like structure. The accurate spectroscopy of excited states at energies above the α emission threshold is fundamental to benchmark the calculations of theoretical models aiming to describe clustering in light nuclei.To improve our knowledge of 13C structure, we performed a comprehensive R-matrix fit of α+9Be elastic and inelastic scattering data in the energy region Eα ≈ 3:510 MeV at several backward polar angles. To carefully determine the partial decay widths of states above the α-decay threshold we included in the fit also 9Be(α n)12C cross section data taken from the literature. This analysis allows to improve the (poorly known) spectroscopy of excited states in 13C in the Ex ≈ 12-17 MeV region, and tentatively suggests the presence of a large-deformation negative-parity molecular band.

Decoupled and semi-decoupled bands in Hg197 and Hg199

The structure of decoupled positive-parity and semidecoupled negative-parity bands up to high spin in $^{197,199}\mathrm{Hg}$ has been studied using multinucleon transfer reactions with the Gammasphere array. A positive-parity band in $^{199}\mathrm{Hg}$ with the ${(\ensuremath{\nu}{i}_{13/2})}^{3}$ decoupled configuration that deexcites to levels in the negative-parity sequences is newly established. The semidecoupled sequences in both isotopes are extended to higher spin. Rotation-aligned angular momenta and crossing frequencies determined from experiment are in fair agreement with those from cranking calculations. A transition from oblate collective rotation at low spin to triaxial noncollective shapes at high spin is indicated.

Evolution of collectivity and evidence of octupole correlations in Br73

High-spin states in the Br73 nucleus have been populated via the Cr50(Si28,αp)Br73 fusion evaporation reaction with a beam energy of 90 MeV. The deexciting gamma rays were detected using the Indian National Gamma Array (INGA). Using the γ-γ coincidence technique, two new bands and eight new interconnecting transitions have been added. The strong interconnecting E1 transitions, between positive and negative parity bands, ensure the existence of octupole correlations at low spin. Line shapes have been observed for 17 transitions, which were analyzed by the Doppler-shift attenuation method to determine the lifetime of excited states of the yrast negative parity band and its signature partner band along with the positive parity band. The deduced transitional quadrupole moments Qt for the ground state band decrease with increasing spin, with their values ranging from 2.88 to 1.00 eb. A similar trend in the quadrupole moment has also been observed for the signature partner as well as for the positive parity band. This decrease in Qt with increasing spin for these bands is interpreted in terms of the cranked Nilsson-Strutinsky model and total Routhian surface calculations, which indicate possible band termination at higher spin.

Testing the core-cluster model calculations for some heavy deformed nuclei

In this work, the spectra of some even–even isotopes are studied by selecting core-cluster decomposition of the parent nucleus. The considered nuclei lie in the rare-earth and the transition metal regions. The Schrödinger equation can be solved using Bohr–Sommerfeld relation and the modified Woods–Saxon beside Coulomb potentials to reproduce the spectra of these isotopes with mass number [Formula: see text]. The theoretical calculations of the excitation energies of the ground state rotational band are compared to the experimental data. The cluster model calculations show a good agreement with the experimental data for the transitional and rotational nuclei more than the vibrational nuclei. Some negative parity bands of the chosen nuclei are studied. The core-cluster charge products are correlated with the transition probability [Formula: see text].

α-cluster structure in 62,64Ge described by the local potential approach

The unstable nuclei 62Ge and 64Ge are analyzed in terms of the α + core structure applying a nuclear potential with (1 + Gaussian)×(W.S. + W.S.3) shape. The ground state bands of 62Ge and 64Ge and first negative parity band of 64Ge are calculated and compared with experimental data. The calculated 64Ge ground state band gives a good account of the experimental energies from 0+ to 8+ state. The rms intercluster separations and B(E2) transition rates are obtained for the 64Ge ground state band and a discussion is presented.

Investigation of the C14+α molecular configuration in O18 by means of transfer and sequential decay reaction

A multinucleon transfer and cluster-decay experiment, namely Be9(C13,O*18→C14+α)α, was performed at a beam energy of 65 MeV. Resonant states in O18 from 7 to 19 MeV, including some newly observed ones, are reconstructed with high resolution, based on the coincident detection of various combinations of the final fragments. The α-decay branching ratios for 14 states are extracted from both the invariant-mass and the missing-mass measurements. Angular correlation analysis was conducted for the 10.3-MeV (4+) state. The present work supports the existence of the positive-parity rotational band associated with the C14+α molecular structure in O18, but the negative-parity band members were not identified.1 MoreReceived 24 February 2019Revised 3 May 2019DOI:https://doi.org/10.1103/PhysRevC.99.064315©2019 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayCluster modelsNuclear structure & decaysTransfer reactionsProperties6 ≤ A ≤ 19Nuclear Physics

The collective Properties of Even-Even164-174 W Isotopes

Ground states bands (GSB) and negative parity band (NPB) of isotopes have been calculated. Bohr-Mottelson (BM), Interacting boson approximation-1(IBM-1) and Interacting vector boson model (IVBM) were used for this purpose. The principal excited state ( ) and the proportion of the second to the primary excited state provide primary information about the properties of the nucleus. The ratio of the gamma energy, over spin of each state as a function of the angular momentum (E-GOS), has been assessed to decide the ground states property of each nucleus. The ratio of energies of ( ) and ( ), states as a function of the angular momentum , have been attracted to decide numerically the properties of the ground states band of all states and all nuclei. The staggering between octupole band and ground state band is found to display a beat pattern as a function of angular momentum . The methods which were used, showed the transitional U(5)-O(6) properties of , the general properties that U(5)-O(6)-SU(3) of , and the transitional properties O(6)-SU(3) of ; while showed the SU(3) properties.

Critical Point of the 152Sm, 154Gd, and 156Dy Isotones

The even—even rare-earth nuclei in U(5)—SU(3) region at neutron number (N) = 90, have been systematically studied using the Bohr—Mottelson Model (BM), Interacting Vector Boson Model (IVBM), and Interacting Boson Model (IBM). The positive ground-state band (GSB) of 152Sm, 154Gd, and 156Dy nuclei has been calculated by using BM, IVBM, and IBM, while the negative-parity band (NPB) of those nuclei are calculated by BM and IVBM only. To determine the intermediate structure, the ratio (r(I + 2)/I) and E-GOS curve (E-Gamma Over Spin) as a function of the spin (I) have been drawn. In the IBM, the calculated reduced B(E2) transition probabilities of the GSB in the 152Sm, 154Gd, and 156Dy nuclei are analyzed and compared to the prediction of vibrational U(5) and rotational SU(3) limits. In the Sm—Dy nuclei with N = 90, the U(5)—SU(3) IBM potential energy surfaces (PES’s) are analyzed and evolve from spherical to deformed shapes with increasing the boson number. The critical phase transition points are identified in the space of model parameters and 152Sm,154Gd, and 156Dy nuclei have been found to be close to critical points.

Description of Energy Levels for 84,86,96,98Sr Isotopes

The positive ground-state band (GSB) of 84,86,96,98Sr has been calculated using the Bohr–Mottelson (BM) model, interacting vector boson model (IVBM), and interacting boson model (IBM-1), while the negative-parity band (NPB) of 84,86,96,98Sr has been calculated using the BM model and IVBM. IBM-1 has been used to calculate the energy of the gamma and beta bands. To determine the properties of the ground-state band, the ratio (r(I +2)/I) and the E-GOScurve (Eγ/I) have been plotted as a function of the spin (I). The potential energy surface (PES) has been calculated using IBM-1. The contour plots of the PESs show that 84,86,96Sr nuclei have vibrational properties and 98Sr has rotational characteristics.

Study of antimagnetic rotation in 109,111Cd

The reduced electric quadrupole transition rates have been calculated for the states of the negative parity bands in [Formula: see text]Cd nuclei using semiclassical model (SCM). The calculated transition rates are found to be decreasing with increasing spin for the states above [Formula: see text] and the dynamic moment of inertia [Formula: see text] of the higher spin states are found to be almost constant. The calculated B(E2) values show better agreement with the experimental B(E2) values for [Formula: see text]Cd. The results for both [Formula: see text]Cd and [Formula: see text]Cd nuclei show a very rapidly increasing value of the [Formula: see text] ratio with increasing spin, suggesting the antimagnetic rotational character of the states lying above the spins [Formula: see text] and [Formula: see text], respectively.

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

Shell-model-like approach based on cranking covariant density functional theory: Band crossing and shape evolution in Fe60

The shell-model-like approach is implemented to treat the cranking many-body Hamiltonian based on the covariant density functional theory including pairing correlations with exact particle number conservation. The self-consistency is achieved by iterating the single-particle occupation probabilities back to the densities and currents. As an example, the rotational structures observed in the neutron-rich nucleus $^{60}$Fe are investigated and analyzed. Without introducing any \emph{ad hoc} parameters, the bandheads, the rotational spectra, and the relations between the angular momentum and rotational frequency for the positive parity band A, and negative parity bands B and C are well reproduced. The essential role of the pairing correlations is revealed. It is found that for band A, the bandcrossing is due to the change of the last two occupied neutrons from the $1f_{5/2}$ signature partners to the $1g_{9/2}$ signature partners. For the two negative parity signature partner bands B and C, the bandcrossings are due to the pseudo-crossing between the $1f_{7/2,~5/2}$ and the $1f_{5/2,~1/2}$ orbitals. Generally speaking, the deformation parameters $\beta$ for bands A, B, and C decrease with rotational frequency. For band A, the deformation jumps from $\beta\sim0.19$ to $\beta\sim0.29$ around the bandcrossing. In comparison with its signature partner band C, band B exhibits appreciable triaxial deformation.