Universität zu Köln

Knafla, Jan Lukas Leberecht ORCID: 0000-0001-7926-4639 (2024). Improving and developing analysis methods and investigation of the prolate-to-oblate shape phase transition in 193Os. PhD thesis, Universität zu Köln.

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Abstract

This dissertation is presented in three parts: the systematic calibration procedure for fast-timing 152 Gd, populated by the experiments is improved by re-measuring the lifetime of the 2+ 1 state in β − -decay of the 152 Eu fast-timing calibration standard. The development of a new γ-γ angular correlation analysis method is discussed, and both, the fast-timing method and the new angular correlation analysis method, are applied in the third project, to analyse a 192 Os(nth. ,γ)193 Os thermal neutron capture experiment. In the first part of the thesis, the improvement of the fast-timing time-walk calibration standard 152 Eu is presented. A 152 Eu source was measured for about 28 days with an experimental setup consisting of four LaBr3 (Ce) detectors, connected to a CAEN V1730 digitizer. Using the centroid 152 Gd was re-measured, shift method for digital fast timing, the lifetime of the 2+ 1 state in improving the uncertainty by an order of magnitude. The impact of this significantly improved lifetime on the systematic fast-timing time-walk calibration procedure and the improved precision of future fast-timing experiments are discussed. Furthermore, a new method for γ-γ angular correlation analysis, using a symmetric ring of HPGe clover detectors, was developed. This method is based on a single-variable parameterization of all crystal positions of the clover ring to derive the effective interaction angles, and attenuation coefficients, directly from the experimental data itself. No detailed simulations of the experimental setup are required. For the experimental validation and as a proof of general applicability, different nuclei are investigated for three separate spectrometers, following the same geometric symmetry. The derived multipole mixing ratios are in excellent agreement with the adopted literature concerning accuracy and precision. In the third part of this thesis, a 192 Os(nth. ,γ)193 Os thermal neutron capture experiment was investigated, using the FIPPS instrument at the Institut Laue-Langevin in Grenoble, France. For this experiment, the spectrometer was equipped with a central ring of HPGe clover detectors and sixteen LaBr3 (Ce) detectors, and lifetime measurements were performed using the well- established generalized centroid difference method. Spin assignments for the low-lying negative parity structure and multipole mixing ratio extraction for several γ-ray transitions were performed using the newly introduced γ-γ angular correlation analysis method. Lifetimes of nine excited states were measured for the first time, and limits for the lifetimes of two additional states were established. The systematic time-walk curve of the experimental setup was calibrated using the improved calibration standard 152 Eu, yielding precise lifetimes, with the uncertainty dominated by the limited statistics of the experiment. Theoretical calculations were performed using the interacting boson-fermion model, based on self-consistent constrained mean-field calculation with the Hartree-Fock-Bogoliubov method with the Gogny-D1M interaction. The results are discussed in the context of the prolate-to-oblate shape phase transition predicted to occur in the neutron-rich A ≈ 190 region.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Knafla, Jan Lukas Leberecht lknafla@ikp.uni-koeln.de orcid.org/0000-0001-7926-4639 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-719501
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:	Natural sciences and mathematics
Uncontrolled Keywords:	Keywords Language Nuclear Structure UNSPECIFIED Lifetime Measurements UNSPECIFIED Angular Correlations UNSPECIFIED
Date of oral exam:	4 December 2023
Referee:	Name Academic Title Jolie, Jan Prof. Dr. Dr. h.c. Reiter, Peter Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/71950