Universität zu Köln

Müscher, Miriam ORCID: 0000-0001-9126-6397 (2024). The low-lying dipole response of medium-mass nuclei - Study of 64Ni using complementary real-photon scattering experiments. PhD thesis, Universität zu Köln.

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Abstract

This thesis deals with the analyses of real-photon scattering experiments to investigate the dipole response of the proton-magic Z=28 nucleus 64Ni. Studies based on the (g,g') reaction are commonly performed up to the particle-separation energies of the nuclide of interest. Up to these energies, E1 decays are mainly associated with the Pygmy Dipole Resonance (PDR) and M1 transitions above 5 MeV with spin-flip resonances, i.e., transitions between spin-orbit partners, in the A approximately 60 mass region. It is of utmost importance to characterize the observed decays, i.e., differentiate between E1 and M1 transitions, for the study of the various dipole-excitation modes. Furthermore, the absolute cross sections have to be determined. Therefore, two complementary (g,g') experiments were performed on 64Ni. On the one hand, an energetically-continuous and mainly-unpolarized photon beam was used at the gELBE facility in Dresden-Rossendorf, Germany, to extract absolute cross sections of observed transitions. On the other hand, quasimonenergetic and linearly-polarized g rays were utilized at the HIgS facility in Durham, US, for the distinction between E1 and M1 transitions. Both complementary measurements are necessary to obtain complete information about the dipole response of atomic nuclei. In all, 87 1− states and 23 1+ levels of 64Ni were firmly identified between 4.3 MeV and the neutron-separation threshold S = 9.7 MeV. For transitions up to 9.3 MeV, absolute energy-integrated cross sections were determined. Besides, absolute photoabsorption cross sections were calculated between 5.86 MeV and 9.05 MeV. The results corresponding to the E1 decay channel were compared to theoretical calculations within the equation of motion (EOM) framework. Furthermore, M1 ground-state decays of 64Ni were interpreted using two shell-model calculations. Besides these comparisons between experiment and theory, systematic investigation of the dipole response in the A approximately 60 mass region were performed. Results of real-photon scattering experiments on 54,56Fe, 58,60Ni, and 66Zn were compiled together with the obtained results of 64Ni and compared. Based on this compilation, it was concluded that the nuclear shell structure has not only an impact on the spin-flip resonance but also on the PDR in this region of the nuclear chart.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Müscher, Miriam muescher@ikp.uni-koeln.de orcid.org/0000-0001-9126-6397 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-727050
Date:	2024
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute for Nuclear Physics
Subjects:	Physics
Uncontrolled Keywords:	Keywords Language E1 response English medium-mass nuclei English real-photon scattering English
Date of oral exam:	16 January 2024
Referee:	Name Academic Title Zilges, Andreas Prof.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/72705