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- Mdletshe, Linda; Yang, X. Q.|Lawrie, E. A.Sithole, Makuhane AbelMajola, Siyabonga Ntokozo ThandoluhleNtshangase, Sifiso SenzoSharpey-Schafer, John FrancisLawrie, J. J.Mthembu, S. H.Bucher, T. D.Msebi, L.Bark, R. A.Avaa, A. A.Chisapi, M. V.Jones, P.Jongile, S.Li, Z. P.Makhathini, L.Malatji, K. L.Netshiya, A. A.Shi, Z.Song, B. Y.Wang, L.Xiang, J.Zhang, S. Q.2022| American Physical So...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 ,and4+ 3 states have been extended up to spins of 12+,15+,and8+, 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.
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- Angular correlation measurements were carried out with a segmented clover detector in a close geometry where the segments were used as individual detectors. This allowed up to 35 unique angles when only front segments are used and up to 140 unique angles when both front and back segments are used. The angular correlation was tested with 60Co and 133Ba sources. The large number of angles and the close geometry, allowing increased efficiency, produced precise angular correlation measurements and allowed the determination of several multipole mixing ratios in 133Cs with a precision comparable to that of the presently adopted values.
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- Ntshangase, Sifiso Senzo; Sharpey-Schafer, John Francis|Majola, S. N. T.Lawrie, E. A.Kardan, A.Bucher, T. D.Lawrie, J. J.Avaa, A. A.Bark, R. A.Chisapi, M. V.Jones, P.Jongile, S.Kenfack, D.Khumalo, T. C.Makhathini, L.Malatji, K. L.Maqabuka, B.Mthembu, S. H.Msebi, L.Netshiya, A. A.O’Neill, G.Shirinda, O.Someketa, P. MZikhali, B. R.Mdletshe, LindaSithole, Makuhane Abel2021| American Physical So...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 γ bands, that appear at low excitation energy. The γ bands can be caused by the precession of a nucleus with triaxial shape, but can also arise from small γ 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 γ 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 γ- γ coincidences, angular distribution ratios and γ-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 νi13/2 configuration while the new 15/2+ band was associated with a coupling of the valence i13/2 neutron with the γ 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 γ-soft nuclear shape should also be investigated in order to firmly establish the nature of the excited positive parity band. Further studies able to distinguish between these alternative descriptions will be beneficial.
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