Universität zu Köln

Esmaylzadeh, Arwin ORCID: 0000-0003-0408-3774 (2023). Investigation of shape coexistence and triaxiality in the neutron-rich A ≈ 100 region using lifetime measurements. PhD thesis, Universität zu Köln.

PDF PhD_Arwin_Esmaylzadeh.pdf Download (18MB)

Abstract

This doctoral thesis presents new experimental findings on the coexistence of nuclear shapes and triaxial deformed nuclei in the neutron rich A ≈ 100 region. In this work, the nuclei 97 Sr, 102Mo, 104,106Ru and 112Pd are investigated by measuring lifetimes of excited states. Lifetimes of low-lying states of 97Sr were measured using the fast-timing method at the Lohengrin spectrometer located at the high-flux nuclear reactor of the Institut Laue-Langevin (ILL) in Grenoble, France. Low-energy states in 102Mo, 104,106Ru and 112Pd were populated by a two-neutron transfer reaction and lifetimes were measured using the recoil distance Doppler shift (RDDS) technique at the Cologne Plunger setup. The 18 O particle beam for the transfer reaction was provided by the 10 MV Tandem accelerator of the Institut für Kernphysik of the Universität zu Köln. The lifetime results derived for 97Sr and 102Mo are discussed within the context of shape coexistence observed in the strontium, zirconium and molybdenum isotopes around neutron number N = 60. The results of 97Sr were compared to interacting boson-fermion model calculations that are based on the microscopic energy density functional. They improve the understanding of the spherical-deformed border at N = 59. The lifetime measurement of a possible high seniority shell-model state gives a hint of the spherical-deformed border. The ρ(E0) strength obtained 102Mo reveals signs of shape coexistence but appears to be from the lifetime of the 0+2 state in less pronounced compared to the isotonic partners in the strontium (98Sr) and zirconium (100Zr) isotopes. The transition strengths deduced from lifetimes of states in the γ band in 102Mo, 104,106Ru and 112Pd were used to interpret the triaxial and γ-soft behavior which is observed in these isotopic chains. The results of 102Mo and 104,106Ru were compared to those obtained within the mapped interacting boson model framework with microscopic input from Gogny mean-field calculations. The interpretations are based on the level energy spacing in the γ band, the transition strengths and the model calculations which underline the description of the nuclei in terms of γ-softness. The experimental data of the 112Pd nucleus was compared to the γ-soft model, the Davydov-Filippov model and a more simple interacting boson model (IBM-1) calculation for the description of γ-softness. The experimental observations suggest a smooth transition from a relatively rigid triaxial nuclear structure in the low spin states to a nearly γ-soft structure in the higher spin states within the γ band.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Esmaylzadeh, Arwin aesmaylzadeh@ikp.uni-koeln.de orcid.org/0000-0003-0408-3774 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-646618
Date:	2023
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 Nuclear Physics English Lifetime measurements English
Date of oral exam:	14 November 2022
Referee:	Name Academic Title Jolie, Jan Professor Zilges, Andreas Professor
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/64661