Search for Collective Strutures in the 186Os And 150Gd Nuclei
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Date
2021
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Publisher
University of Zululand
Abstract
Despite the extensive experimental and theoretical studies that have been conducted onthe low-lying positive-parity 0+2, 2+2, and 4+3states in the transitional deformed nuclei,their microscopic identity remains unclear. It is still one of the major challenges innuclear structure physics to properly understand the nature of these states. To givemore insight on the underlying nature of such states, the excited bands in186Os and150Gd nuclei were investigated at iThemba laboratory for accelerator based sciences(iThemba LABS) using the186W(4He, 4n)186Os and150Sm(4He, 4n)150Gd reactions.The AFRODITEγ-ray spectrometer was used for detection ofγ-ray energies emittedduring the experiments.The decay scheme of186Os has been improved. In particular, a total of 21 newγ-raytransitions have been added to the level scheme of186Os. Most importantly, bandsbuilt on the excited 0+2, 2+2, and 4+3states have not only been confirmed but extendedup to spins of 12+, 15+, and 8+, respectively. In addition, a number of new linkingtransitions were identified. Angular distribution and linear polarization measurementswere employed to accurately assign spins and parities to the known and new levels in186Os. The properties of the excited states in186Os, such as level energies and branch-ing ratios, are interpreted in the context of the systematics of neighboring even-even182−192Os isotopes. Furthermore, the validity of theK-selection rule which emanatesfrom a description based on an axially symmetric nuclear shape is examined. The ob-served decays between the rotational bands support a description whereKis conserved.However, someK-forbidden decays were also identified, thus suggesting that a modelallowing for smallKadmixtures is probably required.The excited bands in this nucleus are compared with the five-dimensional collectiveHamiltonian calculations based on covariant density functional theory (5DCH-CDFT),calculations within the quasiparticle triaxial-rotor (QTR) model and predictions by asimple rotational-vibrational model. The 5DCH-CDFT calculations predict that thecollective structures are associated with different nuclear shapes, varying in quadrupoledeformation, triaxiality andγ-softness.The decay scheme of150Gd has been considerably extended. The data did not providenew information on the low-spin states, which was the initial aim of this experiment,however, 31 new transitions were identified at high spins. The present study for thesetransitions was confined toγ-coincidence analysis. The results for150Gd are presentedin the appendix section.
Description
A thesis submitted to the Faculty of Faculty of Science, Agriculture and Engineering in fulfilment of the requirements for the Degree of Science in the Department of Physics at the University of Zululand, South Africa, 2021.
Keywords
Fusion evaporation reaction, Gamma-ray spectroscopy, Gamma bands, Angular distribution ratios, Linear polarization asymmetry