Universität zu Köln

Harter, Nikolaus Andreas ORCID: 0000-0002-7513-966X (2023). Modernisations and digitalizations of fast timing techniques for γ - γ and e− - γ timing and lifetime measurements in middle-heavy rare earths nuclei. PhD thesis, Universität zu Köln.

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Abstract

This doctoral thesis presents the modernisation and digitalization of two different experimental techniques and the results of different nuclear structure experiments in: The Orange conversion electron spectrometer setup was revised, rebuild in many hardware units and the usability has been restored by extensive software development of a control and acquisition software. Two different measurement modi are supported: a scan modes, which allows for conversion electron spectroscopy of an energy range during γ-source and in-beam measurements and an continuous mode, where one conversion electron energy can be selected by the strenghts of the magnetic field generated by the Orange spectrometer. Additionally, the implementation and validation of the digital fast timing technique with the recently commissioned fast-sampling digitizers Caen V1730 and additionally V1751 has been carried out. The digitizers have been installed and thoroughly been investigated and characterized in terms of time resolution and time walk and the settings of the integrated digital constant fraction discriminators have been optimized for digital fast-timing experiments. Both developments have successfully been commissioned in e− – γ and γ – γ fast-timing lifetime measurements in nuclei belonging to the neutron midshell N = 104, A ≈ 180 region. The lifetime results of four tungsten and osmium isotopes are discussed within the context of the deformation and transitional phenomena in the neutron midshell N = 104 region. All investigated nuclei lie at the edge of the strongly deformed region whose center is represented by the midshell-midshell nucleus 170 Dy. For 176,178,180 W, fast-timing methods using the newly revised and commissioned Orange conversion electron spectrometer and the Cologne HORUS spectrometer were employed. Different fusion evaporation reactions were utilized to populate excited states in these tungsten isotopes, allowing + + + for the measurement of lifetimes for the 2+ 1 , 41 , 61 , and 81 yrast states, with an additional 176 W. The extracted quadrupole deformation parameters, measurement of the 10+ 1 state in reduced transition probabilities, and B4/2 ratios were compared with Interacting Boson Model 1 calculations, confirming the deformed prolate rotor nature of the investigated tungsten isotopes. + + In the case of 182 Os the low-lying yrast states 2+ 1 , 41 , and 61 were studied using the newly implemented and commissioned digital fast-timing technique of the IKP. For the first time, + + lifetimes were determined for the 4+ 1 and 61 states, while the lifetime of the 21 state was re-evaluated to remove inconsistencies in the literature. The obtained lifetimes and extracted B(E2) values were analyzed in terms of collective signatures and transitional phenomena. The + + + calculated B(E2; 4+ 1 → 21 )/B(E2;21 → 01 ) ratio of 1.39(7) supported the interpretation of 182 Os as a rigid rotor, and its significance was discussed alongside neighboring isotopes and isotones within the framework of the interacting boson model 1. Furthermore, the structure of 182 Os was investigated under consideration of the influences of competing factors such as the nearby collective deformed region, γ-soft rotors, X(5) symmetry, and neighboring regions of shape coexistence in low excitation states. The study of higher-lying excitation bands in osmium isotopes and the associated isotones helped explain the structural transitions occurring at 182 Os, shedding light on the interplay of the different structural influences.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Harter, Nikolaus Andreas andreas@harter-home.de orcid.org/0000-0002-7513-966X UNSPECIFIED
URN:	urn:nbn:de:hbz:38-712841
Date:	12 October 2023
Place of Publication:	Köln
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 lifetime measurement, nuclear structure, fast timing, internal conversion, conversion electron spectroscopy, detectors, gamma-gamma timing, electron-gamma timing, constant fraction discrimination, digital CFD, CFD, Orange spectrometer English
Date of oral exam:	25 September 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/71284