Universität zu Köln

Thomas, Tim (2014). Robustness of O(5)/Spin(5)Quantum Numbers in the Interacting Boson (Fermion) Model in Selected Molybdenum and Gold Isotopes. PhD thesis, Universität zu Köln.

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Abstract

The nuclear structure of medium and heavy nuclei represent a huge challenge for theories dealing with nucleon-nucleon interactions. The large number and the complexity of nucleon-nucleon interactions make the description of nuclei far away from closed shells rather difficult. In order to understand the structure of such nuclei, symmetry considerations leading to a reduction of the model space play a major role. In this work the even-even molybdenum isotopes 96Mo and 98Mo and the oddeven gold isotopes 193Au and 195Au were investigated with special regard to the goodness of the O(5) and Spin(5) quantum numbers. Therefore, four inbeam experiments have been performed at the tandem accelerator facilities in Cologne (IKP) and in New Haven (WNSL). The investigation of 96Mo and 98Mo revealed that these nuclei exhibit complex nuclear structures associated with shape coexistence. Based on microscopic considerations the calculations of 98Mo in the framework of the Interacting Boson Model 2 showed a strong mixing of a U(5)-like normal configuration and an O(6)-like intruder configuration. This is experimentally confirmed by quadrupole moments, and the beta deformation of the first excited 2+ states. The successful calculation of 98Mo was extended to 96Mo. The comparison of calculations with single configuration and configuration mixing indicated that the nuclear structure of 96Mo can be understood in terms of shape coexistence. The neutron-proton degree of freedom of the IBFM-2 allowed to understand the mixed symmetry states in the vicinity of configuration mixing and offered a crucial test for the goodness of the O(5) quantum number. In the framework of the Interacting Boson Fermion Model 193Au and 195Au were investigated to test the goodness of the Spin(5) quantum numbers induced by the Bose-Fermi symmetry. The obtained data of the low spin states in 193;195Au fits well to the overall smooth evolution of level energies and transition strengths in the odd-even gold isotopes. This allows to use a simple fourparameter expression based on the eigenfunction of the Bose-Fermi symmetry to describe more than 54 states confirming the conservation of the Spin(5) quantum number.