Three ΔI=1 bands with the πg_{9/2}⊗νg_{9/2} configuration have been identified in _{35}^{74}Br_{39}. Angular distribution, linear polarization, and lifetime measurements were performed to determine the multipolarity, type, mixing ratio, and absolute transition probability of the transitions. By comparing these experimental observations with the corresponding fingerprints and the quantum particle rotor model calculations, the second and third lowest bands are, respectively, suggested as the chiral partner and one-phonon wobbling excitation built on the yrast band. The evidence indicates the first chiral wobbler in nuclei.

High -spin states in 76As have been observed for the first time by using the 4He + 74Ge reaction at beam energies of 58.6 and 62.6 MeV. Two positive -parity and three negative -parity bands have been found in 76As. The two positive -parity bands with 7rg9/2 (R) vg9/2 configurations are tentatively interpreted as chiral doublet bands, which are supported by triaxial particle rotor model calculations. The electric dipole transitions linking the yrast positive- and negative -parity bands are also observed in this work, implying the possible presence of octupole correlations in 76As.

High-spin states in As-74 were studied using the Ge-74(4He, 1p3n) reaction at beam energies of 58.6 and 62.6 MeV. Two positive-and one negative-parity bands have been identified in As-74. The two positive-parity bands are interpreted as chiral doublet bands, which is supported by the triaxial particle rotor model. Three electric dipole transitions linking the yrast positive-and negative-parity bands were also observed in this work, suggesting the existence of octupole correlations in As-74.

Collective structures in 186Os have been investigated through the 186W(4He, 4n) 186Os reaction, at a beam energy of 48 MeV. The low-lying bands built on the excited 0+2 , 2+2 , and 4+3 states have been extended up to spins of 12+, 15+, and 8+, respectively, and a number of new linking transitions were identified. The features of the collective bands in 186Os, such as level energies, are presented in the context of a systematic study of the neighboring even-even 182-192Os isotopes. In addition, the validity of the K-selection rule, stemming from a description based on axial symmetry of the nuclear shape, is examined. The observed decays between the rotational bands support a description where K is conserved. However, some K-forbidden decays were also identified, suggesting that a model allowing for small K admixtures is probably required. The experimental data are further compared with calculations using a five-dimensional collective Hamiltonian based on covariant density functional theory. The calculations predict that the collective bands are associated with different nuclear shapes, varying in quadrupole deformation, triaxiality, and softness.

The spectroscopy of Ge-71 has been investigated via the fusion-evaporation reaction Ge-74(alpha, alpha 3n)Ge-71. Collective structures including a rotational band built on the 15/2(-) octupole state in Ge-71 have been established. The observation of strong E1 transitions and the well-behaved rotational sequence built on the 15/2(-) octupole state provide the first experimental evidence of an octupole rotational band in Ge isotopes, suggesting an enhanced octupole correlation around N = 40 in the A approximate to 70 region. A newly developed semimicroscopic cluster model provides a good description of the octupole characteristics of Ge-71.

The spectroscopy of 62Cu is studied via the 54Cr(12C, 1 p3n) 62Cu fusion-evaporation reaction. On the basis of the gamma -gamma coincidence analysis, angular distributions from oriented states, and linear polarization measurement, three positive-parity and three negative-parity level sequences in 62Cu are observed, including two new gamma -ray transitions and one new level. The collective structures are discussed in terms of the tilted axis cranking covariant density functional theory. Although not firmly confirmed in experiment, the properties of a magnetic rotational structure with the n(f7/2)-1(p3/2 f5/2)2 circle times v(g9/2)1(p3/2 f5/2)4 configuration have been discussed. Its angular momentum generation is probably due to the shears mechanism.

Excited states in Ba-131 and Ce-133 were studied using in-beam gamma-ray spectroscopy through the Sn-122(C-13, 4n) Ba-133 and Te-125(C-12, 4n) Ce-133 reactions, respectively. A strongly coupled band, associated with the nu g(7/2) [404]7/2(+) configuration, was identified in Ba-131 and Ce-133. It is the first time to observe the nu g(7/2) [404]7/2(+) bands in the N = 75 isotones. The signature partners exhibit considerable energy splitting in comparison with those in the pi g(7/2) [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.

Background: The shape of most nuclei is described by its quadrupole deformation (showing the deviation from spherical shape) and its triaxiality (showing the deviation from axial symmetry). Nuclei affected by triaxiality show additional collective rotational bands, called gamma bands, that appear at low excitation energy. The gamma bands can be caused by the precession of a nucleus with triaxial shape, but can also arise from small gamma vibrations around an axially symmetric shape. Purpose: The aim of this work is to search for new collective excitations in 187Os in particular related with the gamma degree of freedom. Methods: The rotational structures of 187Os were populated by the 186W(4He, 3n)187Os reaction at a beam energy of 37 MeV. The measurements of gamma - gamma coincidences, angular distribution ratios and gamma -ray intensities were performed using eleven Compton-suppressed Ge clover detectors. Results: The previously known positive-parity band built on the 11/2+ isomer has been extended up and a new excited positive-parity band built above a 15/2+ state has been observed. The 11/2+ band was assigned a nu i13/2 configuration while the new 15/2+ band was associated with a coupling of the valence i13/2 neutron with the gamma band of the even-even core. The quasiparticle-plus-triaxial-rotor model calculations provide a good agreement with the experimental data for both bands. They describe the 15/2+ band as a collective excitation with respect to the 11/2+ band that corresponds to a precession of the intermediate nuclear axis similarly to the precession of a rotating top. Conclusions: As shown by the calculations, the new rotational band can be understood as resulting from the three-dimensional rotation of a triaxially-deformed nucleus. However, a description based on the vibrations of a gamma -soft nuclear shape should also be investigated in order to firmly establish the nature of the excited positiveparity band. Further studies able to distinguish between these alternative descriptions will be beneficial.

Low- and medium-spin negative-parity bands of Os-187 have been studied using the AFRican Omnipurpose Detector for Innovative Techniques and Experiments (AFRODITE) array, following the W-186(He-4, 3n) Os-187 reaction at a beam energy of 37 MeV. In the current work, all the previously known bands have been significantly extended and three new bands have been added to the level scheme. The angular distribution ratio (R-AD) and polarization measurements have been used to assign spin and parity to the observed new levels. The configurations of some of the bands have been modified. The observed bands are interpreted within the cranked shell model (CSM) and cranked Nilsson-Strutinsky-Bogoliubov (CNSB) formalism. Comparison with experimental data shows good agreements. Systematic comparison with the neighboring Os-185 isotope is also discussed.

Excited states in 131Ba and 133Ce were studied using in-beam γ-ray spectroscopy through the 122Sn(13C,4n)131Ba and 125Te(12C,4n)133Ce reactions, respectively. A strongly coupled band, associated with the νg7/2[404]7/2+ configuration, was identified in 131Ba and 133Ce. 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

Rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the Gd-155(alpha, 2n) Dy-157 and Nd-148(C-12, 5n) Dy-155 reactions at 25 and 65 MeV, respectively. We report high-K bands, which are conjectured to be the first candidates of a K-pi = 2(+)gamma vibrational band, built on the [505]11/2(-) neutron orbital, in both odd-A Dy-155,Dy-157 isotopes. The coupling of the first excited K = 0(+) states or the so-called beta vibrational bands at 661 and 676 keV in Dy-154 and Dy-156 to the [505]11/2(-) orbital, to produce a K-pi = 11/2(-) band, was not observed in both Dy-155 and Dy-157, respectively. The implication of these findings on the interpretation of the first excited 0(+) states in the core nuclei Dy-154 and Dy-156 are also discussed.

Low-spin states of Dy-157 have been studied using the JUROGAM II array, following the Gd-155 (alpha, 2n) reaction at a beam energy of 25 MeV. The level scheme of Dy-157 has been expanded with four new bands. Rotational structures built on the [523]5/2(-) and [402]3/2(+) neutron orbitals constitute new additions to the level scheme as do many of the inter- and intraband transitions. This manuscript also reports the observation of cross I+ -> (I-1)(-) and I- -> (I-1)(+) E1 dipole transitions interlinking structures built on the [523]5/2(-) (band 5) and [402]3/2(+) (band 7) neutron orbitals. These interlacing band structures are interpreted as the bands of parity doublets with simplex quantum number s = -i related to possible octupole correlations.

The 152Sm(16O, 5n)163Yb reaction at a beam energy of 93 MeV was used to study the excited states of 163Yb with the AFRODITE $\gamma$-ray spectrometer at iThemba LABS. The level scheme of 163Yb has been extended and new rotational bands established. The band based on the ground-state has been extended from a spin of 11/2- to spin 43/2-. A high-K band based on the neutron [505]11/2- Nilsson orbital has been observed and is reported for the first time in this work. Additional new states in 163Yb were observed which all decay to the yrast band. Some of these states are placed in a sequence which is conjectured to be a $ \gamma$ band involving a coupling with the i13/2[642]5/2+ neutron orbital. The band structures are discussed with reference to Cranked Shell Model (CSM) calculations and a systematic comparison with the neighbouring nuclei.

A comprehensive systematic study is made for the collective beta and gamma bands in even-even isotopes with neutron numbers N = 88 to 92 and proton numbers Z = 62 (Sm) to 70 (Yb). Data, including excitation energies, B(E0) and B(E2) values, and branching ratios from previously published experiments are collated with new data presented for the first time in this study. The experimental data are compared to calculations using a five-dimensional collective Hamiltonian (5DCH) based on the covariant density functional theory (CDFT). A realistic potential in the quadrupole shape parameters V (beta, gamma) is determined from potential energy surfaces (PES) calculated using the CDFT. The parameters of the 5DCH are fixed and contained within the CDFT. Overall, a satisfactory agreement is found between the data and the calculations. In line with the energy staggering S(I) of the levels in the 2(gamma)+ bands, the potential energy surfaces of the CDFT calculations indicate gamma-soft shapes in the N = 88 nuclides, which become gamma rigid for N = 90 and N = 92. The nature of the 0(2)(+) bands changes with atomic number. In the isotopes of Sm to Dy, they can be understood as beta vibrations, but in the Er and Yb isotopes the 0(2)(+) bands have wave functions with large components in a triaxial superdeformed minimum. In the vicinity of Sm-152, the present calculations predict a soft potential in the beta direction but do not find two coexisting minima This is reminiscent of Sm-152 exhibiting an X(5) behavior. The model also predicts that the 0(3)(+) bands are of two-phonon nature, having an energy twice that of the 0(2)(+) band. This is in contradiction with the data and implies that other excitation modes must be invoked to explain their origin.

© 2019 American Physical Society Published version Majola, S. N. T.; Bark, R. A.; Bianco, L.; Bucher, T. D.; Bvumbi, S. P.; Cullen, D. M.; Garrett, P. E.; Greenlees, P. T.; Hartley, D.; Hirvonen, J.; Jakobsson, U.; Jones, P. M.; Julin, R.; Juutinen, S.; Ketelhut, S.; Kheswa, B. V.; Korichi, A.; Lawrie, E. A.; Masiteng, P. L.; Maqabuka, B.; Mdletshe, L.; Minkova, A.; Ndayishimye, J.; Nieminen, P.; Newman, R.; Nyakó, B. M.; Ntshangase, S. S.; Peura, P.; Rahkila, P.; Riedinger, L. L.; Riley, M.; Roux, D.; Ruotsalainen, P.; Saren, J.; Sharpey-Schafer, J. F.; Scholey, C.; Shirinda, O.; Sithole, A.; Sorri, J.; Stolze, S.; Timár, J.; Uusitalo, J.; Zimba, G.

The collective structures of Ge-75 have been studied for the first time via the Ge-74(alpha, 2p1n)Ge-75 fusion-evaporation reaction. Two negative-parity bands and one tentative positive-parity band built on the nu p(1/2), nu f(5/2), and nu g(9/2) 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 Ge-75. The properties of the bands in Ge-75 are analyzed in comparison with the triaxial particle rotor model calculations.

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.