Universität zu Köln

Weinert, Michael ORCID: 0000-0002-1572-7734 (2022). Investigation of Microscopic Structures in the Low-Energy Electric Dipole Response of 120Sn using Consistent Experimental and Theoretical Observables and Digital Signal Processing for Nuclear Physics Experiments. PhD thesis, Universität zu Köln.

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Abstract

This thesis consists of two parts which deal with the low-energy electric dipole response (LEDR) of atomic nuclei and the development and commissioning of a digital data acquisition system for nuclear-structure experiments, respectively. A term commonly found in the literature for the overall LEDR of atomic nuclei is Pygmy Dipole Resonance (PDR), which was historically used to imply the picture of a neutron-skin oscillation. Since the underlying mechanisms in the LEDR region have been found to be diverse, the term PDR was avoided within this thesis, unless referring explicitly to a neutron-skin oscillation. Part I tries to uncover the generating nuclear-structure features at play in the LEDR of 120Sn below the neutron-separation threshold via two complementary experiments and their theoretical comprehension. The conducted 120Sn(a,a'g) and 119Sn(d,pg) experiments are presented and nuclear-structure calculations performed within the Quasiparticle-Phonon-Model (QPM) are introduced, together with two corresponding reaction-theory approaches. The alpha-scattering experiment was performed at the Research Center for Nuclear Physics in Osaka, Japan, utilizing the combined particle and gamma-ray spectrometer setup CAGRA+GR. Experimental results indicate the presence of isoscalar excitations with a surface-mode character in the LEDR of 120Sn, resembling a neutron-skin oscillation. The 119Sn(d,pg) transfer experiment was performed with the SONIC@HORUS setup at the University of Cologne and constitutes a novel tool to study the microscopic character of individual LEDR states. The remarkable agreement between theoretically obtained (d,pg) cross sections and the experimental data allows to benchmark the predictive power of the QPM and therein employed Energy-Density-Functional calculations. Furthermore, the QPM reproduces the key structural aspects of the LEDR in 120Sn suggested by previous experiments, including the summed B(E1) strength and a transition to more complex configurations at higher excitation energies. It was enforced that theory and experiment are consistently compared via identical observables and striking agreement is found for several experimentally accessible values on a quantitative level. The microscopic information, obtained for the first time in this thesis, complements the knowledge on the relevant nuclear-structure phenomena present in the LEDR of 120Sn. Part II covers a state-of-the-art digital data acquisition system which was designed and commissioned within this thesis. The flexible system exhibits significantly reduced dead time and reaches excellent energy resolution for gamma-ray spectroscopy. It fully replaces the predecessor system and is suitable for all nuclear-physics experiments performed today and in the near future at the 10 MV FN-Tandem accelerator laboratory of the University of Cologne.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Weinert, Michael mweinert@ikp.uni-koeln.de orcid.org/0000-0002-1572-7734 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-653909
Date:	2022
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 Kernphysik; Kernstruktur; Kernstrukturphysik; Pygmy Dipol Resonanz; Pygmy-Dipol-Resonanz; Dipolstärke; Kernanregungen; Transferreaktion; Kollektive Anregung; QPM; (d,p); Quasiparticle-Phonon-Model; Quasiparticle Phonon Model; Kernreaktion; HORUS; SONIC; SONIC@HORUS; CAGRA; CAGRA+GR; DAQ; Datenaufnahme; Digitizer; Energieauflösung; Totzeit; Linearität; ADC; Datenverarbeitung; Signalverarbeitung German nuclear physics; nuclear structure; nuclear structure physics; pygmy dipole resonance; dipole strength; nuclear excitation; transfer reaction; collective excitation; QPM; (d,p); quasiparticle-phonon-model; quasiparticle phonon model; nuclear reaction; HORUS; SONIC; SONIC@HORUS; CAGRA; CAGRA+GR; DAQ; data acquisition; Digitizer; energy resolution; dead time; linearity; ADC; signal processing English
Date of oral exam:	8 December 2022
Referee:	Name Academic Title Zilges, Andreas Prof. Dr. Reiter, Peter Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/65390