Universität zu Köln

Graf von Spee, Franziskus ORCID: 0000-0001-7498-1719 (2024). A search for signs of shape coexistence in mid-shell tellurium isotopes. PhD thesis, Universität zu Köln.

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Abstract

In this work, the structure of mid-shell Te isotopes are investigated. Based on the level schemes, these nuclei seem to be well described by a vibrational model. On the other hand, shape coexistence is suspected, but not firmly established on the basis of experimental data. The nature of the 0_2+ state of these nuclei plays a key role in this discussion as it is the candidate state for the ground state of the intruding configuration. Thus special attention was payed to the properties of these states in this work. The experiments presented here are all carried out at the FN Tandem accelerator at Cologne but different reaction mechanisms and experimental methods are used. Recoil Distance Doppler-shift experiments using (12C,8Be) alpha-transfer reactions on tin targets are performed to determine the lifetimes of low-lying states in tellurium isotopes. This is the first time such reactions are used to populate excited states in mid-shell Te isotopes and thus also the spectroscopic results are presented in detail. It is shown that many low-lying and low-spin states are populated in such reactions. Using the (12C,8Be) alpha-transfer reaction mechanism it is possible to measure the lifetime of the 2_1+, 0_2+ and 2_2+ state in 116Te. Moreover, upper limits are determined for the lifetimes of, among others, the 4_1+, 4_2+ and 2_3+ state. In 118Te, the lifetime of the 0_2+ state is measured and again several upper limits are determined. In 120Te it is only possible to determine an upper limit of the lifetime of the 0_2+ state. The lifetimes of the 2_1+ and 4_1+ states in 118Te are additionally measured using a fusion-evaporation reaction. Furthermore, the beta decay of 116I is investigated to determine spins of excited states and multipolarities of gamma-ray transitions in 116Te. Here, excited 0+ states in 116Te are unambiguously identified for the first time. From the experimental data, level schemes are built, B(E2), B(M1) and rho^2(E0) strengths are calculated. These values are then compared with predictions in the interacting boson model on the one hand --- especially in the U(5) limit ---, and with typical signatures of shape coexistence on the other hand.

Item Type:	Thesis (PhD thesis)
Translated abstract:	Abstract Language UNSPECIFIED English
Creators:	Creators Email ORCID ORCID Put Code Graf von Spee, Franziskus fspee@ikp.uni-koeln.de orcid.org/0000-0001-7498-1719 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-750205
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 shape coexistence English lifetime measurement English angular correlations English alpha transfer UNSPECIFIED
Date of oral exam:	29 October 2024
Referee:	Name Academic Title Dewald, Alfred Professor Reiter, Peter Professor
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/75020