Positive-parity Yrast Band Research Articles

Shell-model-like approach based on cranking covariant density functional theory with a separable pairing force

The shell-model-like approach (SLAP) based on cranking covariant density functional theory (CDFT) with a separable pairing force is developed. The developed cranking CDFT-SLAP with separable pairing force is applied to investigate the rotational spectra in $^{60}$Fe, including the positive-parity yrast band and two negative-parity signature partner bands, in comparison with the cranking CDFT-SLAP with monopole pairing force calculations. Excellent agreement with the available data is achieved.

Isomer spectroscopy in Ba133 and high-spin structure of Ba134

The transitional nuclei $^{134}$Ba and $^{133}$Ba are investigated after multinucleon transfer employing the high-resolution Advanced GAmma Tracking Array coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and after fusion-evaporation reaction at the FN tandem accelerator of the University of Cologne, Germany. The Jπ=19/2+ state at 1942 keV in $^{133}$Ba is identified as an isomer with a half-life of 66.6(20)ns corresponding to a B(E1) value of 7.7(4)×10−6e2fm2 for the Jπ=19/2+ to Jπ=19/2− transition. The level scheme of $^{134}$Ba above the Jπ=10+ isomer is extended to approximately 6 MeV. A pronounced backbending is observed at ℏω=0.38 MeV along the positive-parity yrast band. The results are compared to the high-spin systematics of the Z=56 isotopes. Large-scale shell-model calculations employing the GCN50:82, SN100PN, SNV, PQM130, Realistic SM, and EPQQM interactions reproduce the experimental findings and elucidate the structure of the high-spin states. The shell-model calculations employing the GCN50:82 and PQM130 interactions reproduce alignment properties and provide detailed insight into the microscopic origin of this phenomenon in transitional $^{134}$Ba.

Low-lying positive parity yrast bands in Gd, Dy and Er nuclei for N = 96

The interacting boson model has been applied to calculate the low-lying positive parity yrast bands in Gd, Dy and Er nuclei for N = 96 neutrons. The results closed to the SU(3) limit in this model. Reasonable agreement with available energies and B(E2) transition rates. The potential energy surfaces (PESs) to the IBM Hamiltonian have been obtained using the intrinsic coherent state.

Lifetimes of excited states in triaxially deformed 107Tc and 109,111,113Rh

Lifetimes of excited states in 107Tc, 109Rh, 111Rh, and 113Rh were measured at GANIL using the Recoil-Distance Doppler Shift method. The neutron-rich nuclei were produced in fission reactions in inverse kinematics with a 238U beam impinging on a 9Be target. Fission fragments were identified event-by-event in the ray-tracing spectrometer VAMOS++ and correlated with prompt $\gamma$ rays observed around the target position with the EXOGAM Ge detector array. Several lifetimes were obtained for states in the positive-parity yrast bands in the four nuclei and compared to triaxial particle-rotor calculations. The results clarify the configuration for the strongest positive-parity band in 107Tc and suggest a gradual increase of triaxial deformation with atomic number Z, reaching almost maximum triaxiality for the neutron-rich Rh nuclei.

Determine the 134–140Nd isotopes identity using IBM and NEF

The property of 134−140Neodymium nuclei have been studied in framework Interacting Boson Model (IBM) and a new method called New Empirical Formula (NEF). The energy positive parity bands of 134−140Nd have been calculated using (IBM) and (NEF) while the negative parity bands of 134−140Nd have been calculated using (NEF) only. The E-GOS curve (Eγ/I) as a function of the spin (I) has been drawn to determine the property of the positive parity yrast band. The parameters of the best fit to the measured data are determined. The reduced transition probabilities B(E2) of these nuclei was calculated. The critical point has been determined for 140Nd isotope. The potential energy surfaces (PESs) to the IBM Hamiltonian have been obtained using the intrinsic coherent state.

Projected Shell Model Description of Positive Parity Band of 130Pr Nucleus

Theoretical investigation of positive parity yrast band of odd-odd 130Pr nucleus is performed by applying the projected shell model. The present study is undertaken to investigate and verify the very recently observed side band in 130Pr theoretically in terms of quasi-particle (qp) configuration. From the analysis of band diagram, the yrast as well as side band are found to arise from two-qp configuration πh 11/2 ⊗ νh 11/2. The present calculations are viewed to have qualitatively reproduced the known experimental data for yrast states, transition energies, and B(M1) / B(E2) ratios of this nucleus. The recently observed positive parity side band is also reproduced by the present calculations. The energy states of the side band are predicted up to spin 25+, which is far above the known experimental spin of 18+ and this could serve as a motivational factor for future experiments. In addition, the reduced transition probability B(E2) for interband transitions has also been calculated for the first time in projected shell model, which would serve as an encouragement for other research groups in the future.

Calculation of the Positive Parity Yrast Bands of 190–198Hg Nuclei

Calculation of the Positive Parity Yrast Bands of 190–198Hg Nuclei

G-factor measurements of high spin states in 108Cd

The g-factors of the rotational states of the positive parity yrast band from spin I=10 + to spin I=16 + in even-even nucleus 108Cd have been measured by the transient-magnetic-field ion implantation perturbed angular distribution method. The high spin states of 108Cd were populated by the fusion evaporation reaction 76Ge (37Cl, 1p4n) 108Cd. The measured g-factors increase gradually as the spin increases from 10 + to 16 + due to the g7/2 neutron alignment. The g7/2 neutrons are fully aligned at spin I=16+. This state is the band head state of the anti-magnetic rotational band in 108Cd. The measured g-factor of this state is -0.09. The present results support that this band head state may have the configuration \(\pi (g_{9/2})^{-2}_{J=0}\otimes \nu (h_{11/2})^{2}_{J=10}\nu (g_{7/2})^{2}_{J=6}\).

A study of positive parity yrast bands of 230–240U and 236–242Pu nuclei

The projected shell model is used to study the yrast positive parity bands in 230–240U and 236–242Pu nuclei. The energy levels, deformation systematics, E2 transition probabilities and g-factors are calculated. The calculation reproduces the observed positive parity yrast bands and B(E2) transition probabilities. The observed deformation trend of low-lying states in Uranium and Plutonium nuclei depends on the occupation of down-sloping components of high j orbits in the valence space. The low-lying states of yrast spectra are found to arise from 0-quasiparticle (qp) intrinsic states, whereas the high spin states possess multi-qp structure. The theoretical results of g-factors of Pu isotopes predict an increase in g-factors at higher spins arising from the alignment of protons in 1i13/2 orbit. The predicted values of B(E2)s and g-factors for higher spin states in Pu isotopes have to be verified experimentally.

High-Spin States and Level Structure in Stable Nucleus Strontium-84

High-spin states of 84Sr are populated through the reaction 70Zn (18O, 4n) 84Sr at the beam energy of 75 MeV. The measurements of excitation functions, γ-γ coincidences, directional correlations of oriented states (DCO) ratios and γ-transition intensities are performed using eight anticompton HPGe detectors and one planar HPGe detector. Based on the experimental results, we establish a new level scheme of 84Sr, in which 12 new states and nearly 30 new γ-transitions are identified in the present work. The positive-parity yrast band is extended to spin Iπ = 24+, while one negative-parity band is extended to spin Iπ = 19− and it is found that the even-spin and odd-spin members in high-spin states show the nature of signature staggering. The deformation of 84Sr is studied by calculating the total-Routhian-surfaces (TRS) of positive-parity yrast states in the cranked shell model formalism.

Signature splitting and magnetic rotation in86Y

Based on recent experimental data, the band structure of the odd-odd nucleus ${}^{86}$Y has been studied. The positive-parity yrast band built on the configuration $\ensuremath{\pi}{g}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}^{\ensuremath{-}1}$ shows a large signature splitting, and a signature inversion occurs at $I\ensuremath{\sim}13\ensuremath{\hbar}$. The signature inversion is interpreted by the competition between single-particle and collective excitations in this nucleus. The negative-parity dipole band, which is probably connected with magnetic rotation, is assigned to the configurations $\ensuremath{\pi}{g}_{9/2}^{2}{({p}_{3/2}/{f}_{5/2})}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}^{\ensuremath{-}1}$ before and to $\ensuremath{\pi}{g}_{9/2}^{2}{({p}_{3/2}/{f}_{5/2})}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}^{\ensuremath{-}3}$ after the alignment. Self-consistent titled axis cranking calculations based on relativistic mean-field theory are performed to interpret the rotational structure. Characteristic features of magnetic rotation are found for the negative-parity band.

Microscopic study of positive-parity yrast bands of 224−234Th isotopes

The positive-parity bands in 224 − 234Th are studied using the projected shell model (PSM) approach. The energy levels, deformation systematics, B(E2) transition probabilities and nuclear g-factors are calculated and compared with the experimental data. The calculation reproduces the observed positive-parity yrast bands and B(E2) transition probabilities. Measurement of B(E2) transition probabilities for higher spins and g-factors would be a stringent test for our predictions. The results of theoretical calculations indicate that the deformation systematics in 224 − 234Th isotopes depend on the occupation of low k components of high j orbits in the valence space and the deformation producing tendency of the neutron–proton interaction operating between spin orbit partner (SOP) orbits, the [(2g9/2) π –(2g7/2) ν ] and [(1i13/2) π –(1i11/2) ν ] SOP orbits in the present context. In addition, the deformation systematics also depend on the polarization of (1h11/2) π orbit. The low-lying states of yrast spectra are found to arise from 0-quasiparticle (qp) intrinsic states whereas the high-spin states turn out to possess composite structure.

Signature splitting inversion and backbending in80Rb

High-spin states of ${}^{80}$Rb are studied via the fusion-evaporation reactions ${}^{65}$Cu+${}^{19}$F, ${}^{66}$Zn+${}^{18}$O, and ${}^{68}$Zn+${}^{16}$O with the beam energies of 75 MeV, 76 MeV, and 80 MeV, respectively. Twenty-three states with twenty-eight \ensuremath{\gamma} transitions are added to the previously proposed level scheme, where the second negative-parity band is significantly pushed up to spins of 22${}^{\ensuremath{-}}$ and 15${}^{\ensuremath{-}}$ and two sidebands are built on the known first negative-parity band. Two successive band crossings with frequencies 0.51 MeV and 0.61 MeV in the \ensuremath{\alpha} $=$ 0 branch as well as another one in the \ensuremath{\alpha} $=$ 1 branch of the second negative-parity band are observed. Signature inversions occur in the positive-parity and first negative-parity bands at the spins of 11$\ensuremath{\hbar}$ and 16$\ensuremath{\hbar}$, respectively. The signature splitting is seen obviously in the second negative-parity band, but the signature inversion is not observed. It is also found that the structure of the two negative-parity bands is similar to that of its isotone ${}^{82}$Y. Signature inversion in the positive-parity yrast band with configuration \ensuremath{\pi}${g}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}$ in this nucleus is discussed using the projected shell model.

Microscopic analysis of band structures in odd mass 79–89Y isotopes

The positive-parity yrast bands of 79, 81, 83, 85, 87, 89Y isotopes have been studied using the projected shell model (PSM). Nuclear-structure properties like yrast spectra, transition energies, band diagrams, kinetic moment of inertia, rotational frequencies and reduced transition probabilities (B(M1) and B(E2) are calculated. The results obtained from the PSM calculations are also compared with the available experimental as well as theoretical data and, in general, a reasonable agreement is obtained between them. Calculations in the present work also predict that these isotopes have multi-quasiparticle structure.

High-spin yrast states in theγ-soft nuclei135Pr and134Ce

High-spin states have been studied in Pr-135(59), populated through the Cd-116(Na-23,4n) reaction at 115 MeV, using the Gammasphere gamma-ray spectrometer. The negative-parity yrast band has been significantly extended to spin similar to 45 (h) over bar and excitation energy 21.5 MeV, showing evidence for several rotational alignments. The positive-parity yrast band of Ce-135(58), populated through the p4n channel of this reaction, was also populated to spin similar to 38 (h) over bar and excitation energy 18 MeV. Cranking calculations indicate that these nuclei are soft with respect to the triaxiality parameter gamma and that several competing nuclear shapes occur at high spin.

Investigation into the rotational bands of 185Pt with the particle-rotor model

Theoretical calculations have been performed for the ν9/2+[624](i13/2) and ν7/2−[503]( f7/2) bands of 185Pt in the framework of particle-rotor model. The band properties of signature splitting and configuration mixing have been analyzed. The level energy and signature splitting before the band crossing can be well interpreted by introducing triaxiality. The positive-parity yrast band is proposed to be dominated by the ν9/2+[624](i13/2) component, while the negative-parity band shows strong mixing of ν7/2−[503](f7/2) and ν9/2−[505](h9/2) configurations.

High-spin states and level structure inRb84

High-spin states in $^{84}\mathrm{Rb}$ have been studied by using the $^{70}\mathrm{Zn}$($^{18}\mathrm{O},p3n)$$^{84}\mathrm{Rb}$ reaction at beam energy of 75 MeV. The $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidence, excitation function, and ratios for directional correlation of oriented states were determined. A new level scheme was established in which the positive- and negative-parity bands have been extended up to ${17}^{+}$ and ${17}^{\ensuremath{-}}$ with an excitation energy of about 7 MeV. The signature splitting and signature inversion of the positive-parity yrast band were observed. To understand the microscopic origin of the signature inversion in the yrast positive-parity bands of doubly odd Rb nuclei, as an example, we performed calculations using the projected shell model to describe the energy spectra in $^{84}\mathrm{Rb}$. It can be seen that the main features are reproduced in the calculations. This analysis shows that the signature splitting, especially its inversion, can be reproduced by varying only the $\ensuremath{\gamma}$ deformation with increasing spin. To research the deformation of $^{84}\mathrm{Rb}$ carefully, we calculate the total Routhian surfaces of positive-parity yrast states by the cranking shell model formalism. In addition, the results of theoretical calculations about the negative-parity yrast band in $^{84}\mathrm{Rb}$ with configuration $\ensuremath{\pi}({p}_{3/2},{f}_{5/2})\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}$ are compared with experimental data, and a band diagram calculated for this band is also shown to extract physics from the numerical results.

Structure change of 156Yb at high-spin states

High-spin states of 156Yb have been studied via the 144Sm(16O,4n)156Yb fusion-evaporation reaction at beam energy 102 MeV. The positive-parity yrast band and negative-parity cascade have been extended up to higher-spin states, respectively. The characteristics of the negative-parity sequence above the 25− state may related to the excitation from the nucleon in the Z = 64, N = 82 core. The E-GOS curve for the positive-parity yrast sequence in 156Yb indicate that this nucleus may undergo an evolution from quasivibrational to quasirotational structure with increasing angular momentum. The Cranked Woods–Saxon–Strutinsky calculations by means of Total–Routhian–Surface (TRS) methods has been made to understand this structure change.

High-spin states inYb156and structure evolutions at large angular momenta in even-AYb isotopes

High-spin states of (156)Yb have been studied via the (144)Sm((16)O,4n)(156)Yb fusion-evaporation reaction at beam energy 102 MeV. The positive-parity yrast band and negative-parity cascade have been extended up to higher-spin states, respectively. In the present work, the negative-parity sequence above the 25(-) state was found to be irregular and fragment into many parallel branches. This pattern may related to the excitation from the nucleon in the Z=64,N=82 core. The characteristics of alignment plot and E-GOS curve for the positive-parity yrast sequence in (156)Yb indicate that this nucleus may undergo an evolution from quasivibrational to quasirotational structure with increasing angular momentum. Based on a systematic summary of the available experimental alignments for the even-A (156,158,160,162,164)Yb isotopes, the structural evolutions induced by the increase in angular momentum, as well as by the change in neutron numbers, in these even-A Yb isotopes have been discussed in comparison with the cranked Woods-Saxon-Strutinsky calculations by means of total-Routhian-surface (TRS) methods.

Loss of collectivity in 79Rb

High-spin states in 79Rb were populated in the reaction $\mathrm{^{63}Cu \ensuremath(^{19}F, p2n) ^{79}Rb}$ at E(beam) = 60 MeV. The lifetimes of the excited states of the $\pi \ensuremath g_{\frac{9}{2}}$ positive-parity yrast band and of the $\pi \ensuremath p_{\frac{3}{2}}$ negative-parity band in 79Rb were measured by the Doppler Shift Attenuation Method. The deduced transition quadrupole moments Qt are found to have a decreasing trend with rotational frequency for both the bands, consistent with those found experimentally in neighbouring nuclei.