Positive-parity Band Research Articles

Excited states in129I

Excited states in ${}^{129}$I were populated with the ${}^{124}$Sn(${}^{7}$Li,$2n$) reaction at 23 MeV. In-beam measurements of $\ensuremath{\gamma}$-ray coincidences were performed with an array of eight HPGe detectors and five LaBr${}_{3}$(Ce) scintillation detectors. Based on the $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence data, a positive parity band structure built on the $7/{2}^{+}$ ground state was established and the $\ensuremath{\pi}{g}_{7/2}$ configuration at oblate deformation was assigned to it. The results are compared to interacting Boson-Fermion model (IBFM) and total Routhian surface (TRS) calculations.

Band structure of235U

Over a period of several years we have performed three separate experiments at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron in which ${}^{235}$U (thick target) was Coulomb-excited. The program involved stand-alone experiments with Gammmasphere and with the 8pi Spectrometer using ${}^{136}$Xe beams at 720 MeV, and a CHICO-Gammasphere experiment with a ${}^{40}$Ca beam at 184 MeV. In addition to extending the known negative-parity bands to high spin, we have assigned levels in some seven positive-parity bands which are in some cases (e.g., $[631]1/2$, $[624]7/2$, and $[622]5/2$) strongly populated by $E3$ excitation. The CHICO data have been analyzed to extract $E2$ and $E3$ matrix elements from the observed yields. Additionally, many $M1$ matrix elements could be extracted from the $\ensuremath{\gamma}$-ray branching ratios. A number of new features have emerged, including the unexpected attenuation of magnetic transitions between states of the same Nilsson multiplet, the breakdown of Coriolis staggering at high spin, and the effect of $E3$ collectivity on Coriolis interactions.

Reflection symmetry of the near-yrast excitations in145Ba

Excited states in ${}^{145}$Ba, populated in spontaneous fission of ${}^{248}$Cm, have been studied by means of $\ensuremath{\gamma}$ spectroscopy, using high-fold $\ensuremath{\gamma}$ coincidences measured with the EUROGAM2 array of Ge detectors. The 507.7-keV level, which has been assigned in this work spin and parity 9/2${}^{+}$, belongs to the ${i}_{13/2}$ intruder band. We have identified in ${}^{145}$Ba a new 9/2${}_{2}^{\ensuremath{-}}$ level at 346.3 keV and a band on top of it. The negative parity indicates that it is not due to an octupole excitation. The position of the 5/2${}^{\ensuremath{-}}$ ground state, relative to the positive-parity band, could be reproduced by calculations with a reflection-symmetric potential and we do not observe a parity doublet to the ground state. Therefore we conclude that octupole excitations in ${}^{145}$Ba are most likely due to octupole vibrations coupled either to the reflection-symmetric ground state or to the ${i}_{13/2}$, decoupled neutron configuration.

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.

THEORETICAL INVESTIGATION OF POSITIVE PARITY BAND STRUCTURE OF Y AND Nb ISOTOPES

The positive parity band structure of odd mass neutron-rich 97 – 103 Y and 99 – 105 Nb nuclei has been studied using microscopic technique known as the projected shell model (PSM) with the deformed single-particle states generated by the standard Nilsson potential. The nuclear structure properties like yrast spectra, energy splitting, moment of inertia, rotational frequencies and reduced transition probabilities B(M1) and B(E2) have been calculated and their comparison with the available experimental data has been made. A shape evolution has also been predicted in these isotopes as one moves from 97 Y to 99 Y and 99 Nb to 101 Nb . The PSM calculations also demonstrate the multi-quasiparticle structure in these nuclei.

Band structures in106Pd

The high spin states of ${}^{106}$Pd have been investigated with in-beam $\ensuremath{\gamma}$-ray spectroscopic methods using the ${}^{100}$Mo(${}^{11}\text{B},1p4n$)${}^{106}$Pd reaction at a beam energy of 60 MeV. All earlier known bands were extended considerably and additional bands were identified. The configurations of these bands are discussed on the basis of the experimental aligned angular momenta and total Routhian surface calculations. Both two-quasineutron and two-quasiproton structures have been found in ${}^{106}$Pd. The nonyrast low-lying positive-parity band was interpreted as a $\ensuremath{\gamma}$-vibrational band.

Observation of positive-parity bands in109Pd and111Pd: Enhancedγsoftness

The neutron-rich nuclei $^{109}$Pd and $^{111}$Pd were produced as fission fragments following the $^{30}$Si + $^{168}$Er reaction at 142 MeV. Using the identification based on the coincidences with the complementary fission fragments, the only positive-parity bands observed so far in $^{109}$Pd and $^{111}$Pd emerged from this work. A band, built on top of the 5/2$^+$ ground state exhibiting $\Delta I$ = 1 energy-level staggering, was observed in each of these nuclei. Both nuclei of interest, $^{109}$Pd and $^{111}$Pd, are suggested to lie in the transitional region of Pd isotopes of maximum $\gamma$-softness. The ground states of both nuclei are predicted by TRS calculations to be extremely $\gamma$-soft with shallow triaxial minima. The first crossing in the new bands is proposed to be due to an alignment of $h^2_{11/2}$ neutrons.

SEARCH FOR TWO-PHONON OCTUPOLE VIBRATIONAL BANDS IN 88, 89, 92, 93, 94, 96Sr AND 95, 96, 97, 98Zr

Several new gamma transitions were identified in 94 Sr , 93 Sr , 92 Sr , 96 Zr and 97 Zr from the spontaneous fission of 252 Cf . Excited states in 88, 89, 92, 94, 96 Sr and 95, 96, 97, 98 Zr were reanalyzed and reorganized to propose the new two-phonon octupole vibrational states and bands. The spin and parity of 6+ are assigned to a 4034.5 keV state in 94 Sr and 3576.4 keV state in 98 Zr . These states are proposed as the two-phonon octupole vibrational states along with the 6+ states at 3483.4 keV in 96 Zr , at 3786.0 keV in 92 Sr and 3604.2 keV in 96 Sr . The positive parity bands in 88, 94, 96 Sr and 96, 98 Zr are the first two-phonon octupole vibrational bands based on a 6+ state assigned in spherical nuclei. It is thought that in 94, 96 Sr and 96, 98 Zr a 3- octupole vibrational phonon is weakly coupled to an one-phonon octupole vibrational band to make the two-phonon octupole vibrational band. Also, the high spin states of odd-A95 Zr and 97 Zr are interpreted to be generated by the neutron 2d5/2 hole and neutron 1g7/2 particle, respectively, weakly coupled to one- and two-phonon octupole vibrational bands of 96 Zr . The high spin states of odd-A87 Sr are interpreted to be caused by the neutron 1g9/2 hole weakly coupled to 3- and 5- states of 88 Sr . New one- and two-POV bands in 95, 97 Zr and 87, 89 Sr are proposed, for the first time, in the present work.

Magnetic rotation in doubly odd nucleus 114In

Abstract High spin states of 114In were investigated via the reaction Pd 110 ( Li 7 , 3 n ) at beams energy of 26 and 28 MeV. The newly observed magnetic dipole bands of 114In in the experiment have been investigated employing the self-consistent tilted axis cranking relativistic mean-field theory based on a point-coupling interaction. A large backbend in the yrast band has been reproduced by the theory based on configuration involving alignment of a pair of positive-parity g 7 / 2 / d 5 / 2 neutrons. According to the experimental characteristics and theoretical calculations, the positive-parity dipole band has been assigned as a magnetic rotation band. In addition, the experimental results are also compared with a semiclassical geometric model that employs effective interactions between the proton holes and neutrons as an alternate interpretation for the shears mechanism.

ROTATIONAL BANDS AND ELECTROMAGNETIC TRANSITIONS OF SOME EVEN–EVEN NEODYMIUM NUCLEI IN PROJECTED HARTREE–FOCK MODEL

Rotational structures of even–even 150 – 160 Nd nuclei are studied with the self-consistent deformed Hartree–Fock (HF) and angular momentum (J) projection model. Spectra of ground band, recently observed K = 4-, K = 5- and a few more excited, positive and negative parity bands have been studied up to high spin values. Apart from these, detailed electromagnetic properties (like E2, M1 matrix elements) of all the bands have been obtained. There is substantial agreement between our model calculations and available experimental data. Predictions are made about the band structures and electromagnetic properties of these nuclei. Some 4-qasiparticle K-isomeric bands and their electromagnetic properties are predicted.

STUDYING THE NUCLEAR STRUCTURE OF EVEN-EVEN DEFORMED GERMANIUM NUCLEUS

In the present work, the interacting boson model(IBM-1) for s and d boson is used to calculate the energy levels of the positive parity bands, electric quadrupole moments, E2-transition probabilities B(E2)in particular between states which may be affected by the finite boson number N=Nذ+Nُ=2+5=7 of even-even nucleus . This nucleus is belong to SU(5)-SU(3) dynamical symmetry .The calculated results of this study are compared with the available experimental data and they found to be in a very good agreement.

High-spin states in127I

In-beam $\ensuremath{\gamma}$ spectroscopy of the stable nucleus ${}^{127}$I has been studied experimentally using the ${}^{124}$Sn(${}^{7}$Li, 4$n\ensuremath{\gamma}$)${}^{127}$I reaction at a beam energy of 32 MeV. The high-spin level scheme of ${}^{127}$I is extended significantly. Negative-parity levels built on the $11/{2}^{\ensuremath{-}}$, $\ensuremath{\pi}{h}_{11/2}$ particle state are observed up to $(35/{2}^{\ensuremath{-}})$ and described as a decoupled band, extending our knowledge of decoupled structures to the most neutron-rich stable iodine isotope. Two $\ensuremath{\Delta}I=2$ yrast positive-parity sequences are proposed to be associated with the $\ensuremath{\pi}{g}_{7/2}$ configuration due to observations of several strong interband transitions, and two weakly populated $\ensuremath{\Delta}I=2$ positive-parity bands are newly identified and interpreted as arising mainly from the $\ensuremath{\pi}{d}_{5/2}$ configuration. Three-quasiparticle configurations are assigned to the ${I}^{\ensuremath{\pi}}=15/{2}^{+}$ and $23/{2}^{+}$ states according to the existing knowledge in neighboring nuclei; irregular noncollective and regular collective excitations built on these two ($15/{2}^{+}$ and $23/{2}^{+}$) states are observed to coexist at similar energies. The observed three-quasiparticle band structures are further interpreted with the aid of configuration-constrained potential energy surface calculations.

High-spin structure of104Pd

The high-spin structure of the nucleus 104Pd was studied through the 96Zr(13C,5n) reaction at incident energies of 51 and 58 MeV, using the Euroball IV γ-ray spectrometer in conjunction with the DIAMANT charged-particle array. Several new medium- and high-spin bands were revealed. The already known positive-parity yrast and the negative-parity cascades were extended up to Ex∼13, ∼11, and ∼9 MeV with Iπ=(26+), Iπ=(23−), and (20−), respectively. The deduced band structures were compared with Woods-Saxon total Routhian surface (TRS) calculations. In addition, non-yrast low-lying positive-parity bands were identified, which were assigned to soft γ-vibrational excitations.2 MoreReceived 13 January 2012DOI:https://doi.org/10.1103/PhysRevC.85.044303©2012 American Physical Society

Observation of new levels and proposed octupole correlations in neutron-rich150Ce

Background: The very neutron-rich ${}^{150}$Ce is located at the edge of the $Z=56$, $N=88$ octupole deformed island. Studying its high spin states and octupole correlations is important for systematically understanding the nuclear structural characteristics in this region. Purpose: To investigate the high spin state levels and to search for octopole correlations in ${}^{150}$Ce. Methods: The high spin states of ${}^{150}$Ce are studied by measuring the prompt $\ensuremath{\gamma}$ rays in the spontaneous fission of ${}^{252}$Cf. The data analysis uses the $\ensuremath{\gamma}$-$\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidence methods. The $\ensuremath{\gamma}\ensuremath{\rightarrow}\ensuremath{\gamma}(\ensuremath{\theta})$ angular correlation measurements are used to determine the spin and indirectly determine the parity of particular levels. Results: A new level scheme of ${}^{150}$Ce is established. A total of 47 new transitions and 25 new levels are identified, compared with previous results. Six collective bands have been observed, and five of them are newly established. An octupole band structure with $s=+1$ in ${}^{150}$Ce has been proposed. Systematic analysis of the $B(E1)/B(E2)$ branching ratios, the levels of the octupole bands, the energy differences between negative- and positive-parity bands, and the moments of inertia of the bands is carried out for ${}^{144,146,148,150}$Ce. This analysis gives evidence for our assignment of octupole correlations in ${}^{150}$Ce. The other characteristics of the octupole bands are discussed. Conclusions: An octupole band structure is proposed in ${}^{150}$Ce. The octupole correlations in ${}^{150}$Ce are weaker and show more instability than the neighboring lighter Ce isotopes.

Small quadrupole deformation for the dipole bands in112In

High spin states in $^{112}$In were investigated using $^{100}$Mo($^{16}$O, p3n) reaction at 80 MeV. The excited level have been observed up to 5.6 MeV excitation energy and spin $\sim$ 20$\hbar$ with the level scheme showing three dipole bands. The polarization and lifetime measurements were carried out for the dipole bands. Tilted axis cranking model calculations were performed for different quasi-particle configurations of this doubly odd nucleus. Comparison of the calculations of the model with the B(M1) transition strengths of the positive and negative parity bands firmly established their configurations.

Critical point symmetries in deformed odd-Anuclei

A scheme that elucidates the nature of critical point symmetries in deformed odd-A nuclei by linking them to critical point symmetries of neighboring even-even nuclei is introduced. Specifically, a new symmetry, called SX(3), is advanced that shows primary characteristics of an assumed strong-coupling limit for odd-A systems. It is found that the SX(3) symmetry can be used to identify the soft collective structures in odd-A system. A preliminary application of the new scheme to describe the lowest positive parity bands of ${}^{193}$Ir is also shown.

Observation of abnormally large radii of nuclei in excited states in the vicinity of neutron thresholds

Differential cross sections for inelastic scattering leading to the excitation of some nuclear states situated near neutron-emission thresholds were analyzed. With the aid of a modified diffraction model, abnormally large radii were found for the 1/21+ state of the 13C nucleus at 3.09 MeV, for the first levels of positive-parity rotational bands in the 9Be (1/2+ level at 1.68 MeV and 5/2+ level at 3.05 MeV) and 11Be (5/2+ level at 1.78 MeV and 3/2+ level at 3.41 MeV) nuclei, and for the 21+ state of the 14Be nucleus at 1.54 MeV and 11− state of the 12Be nucleus at 2.7 MeV. All of these states possess signatures typical of neutron halos.

CONFIGURATION ASSIGNMENT OF THE POSITIVE-PARITY STRUCTURES IN 108Ag

The high-spin states of 108 Ag have been studied by the in-beam γ spectroscopy with the reaction 104 Ru (7 Li ,3n)108 Ag at a beam energy of 33 MeV. The previously known positive-parity band structures have been extended up to higher spins. Their configurations are discussed based on alignments, band-crossing frequencies, and B(M1)/B(E2) ratios.

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.