Karayonchev, Vasil Vasilev ORCID: 0000-0002-6497-0175 (2020). Lifetime measurements in the lead region and the emergence of collectivity in 98Zr. PhD thesis, Universität zu Köln.

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The evolution from the single-particle, seniority-like structure to the emergence of collectivity has been investigated in the lead region through lifetime measurements. The fast-timing, the recoil-distance Doppler shift (RDDS), and the Doppler-shift attenuation (DSA) methods have been employed in the scope of this thesis. Lifetimes of low-lying states in 211At were measured in the 208Pb( 6Li,3n) fusion-evaporation reaction via the fast-timing method and in the 209Bi( 16O, 14C) two-proton transfer reaction via the RDDS and DSA methods. The deduced transition probabilities have been interpreted by two shell-model calculations. One was a multi-j shell-model calculation done using the Kuo-Herling residual interaction. The other one was done using a semi-empirical interaction for protons confined to the single-j 0h9/2 orbital. The Kuo-Herling calculations overestimate some of the ground-state transitions, which has been interpreted as a presence of particle-hole excitation in the ground-state wave function. However, the discrepancy between the calculated values and the measured ones is smaller than in the case of 210Po. This shows that the effects of the particle-hole excitations are reduced when moving away from the 208Pb core. The results from the single-j calculations describe the reduced transition probabilities well, which shows that seniority could be regarded as a good quantum number. The 209Po nucleus was studied in the electron-capture decay of 209At via the fast-timing technique. The deduced transition probabilities were compared to shell-model calculations done using the V low−k approach based on the Bonn nucleon-nucleon potential. The results show that some of the states in 209Po could be interpreted as single-particle neutron-hole states coupled to a 210Po core. However, some additional contributions in the wave functions are needed to describe the experimental data better. The onset of collectivity in the region was studied via fast-timing measurements of the lifetimes of the 4+1 states in 204Po and 206 Po. The nuclei were studied via the 197Au( 11B,3n) and the 198Pt(12C,4n)206Po reactions, respectively. The results indicate that the transition to a collective behavior of the 4+1 states happens below N=122. Additionally, the rapid onset of collectivity in the A ≈ 100 region was investigated in the scope of this thesis. The low-spin structure of the 98Zr nucleus was studied in the 96Zr( 18O, 16O) two-neutron transfer reaction. Lifetimes were deduced using the RDDS and DSA techniques. The results were interpreted by a Monte Carlo shell model and an inter-acting boson model with configuration mixing calculations. Both calculations reproduce most of the data but there are still some open questions regarding the low-spin structure of 98Zr.

Item Type: Thesis (PhD thesis)
CreatorsEmailORCIDORCID Put Code
Karayonchev, Vasil Vasilevkarayon@ikp.uni-koeln.deorcid.org/0000-0002-6497-0175UNSPECIFIED
URN: urn:nbn:de:hbz:38-461253
Date: 2020
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:
RDDS, lifetime measurement, exotic nuclei, nuclear structure, gamma-ray spectroscopy, shell model, fast-timing, DSA, collective excitation, IBMUNSPECIFIED
Date of oral exam: 25 February 2021
NameAcademic Title
Jolie, JanProf.
Dewald, AlfredProf.
Refereed: Yes
URI: http://kups.ub.uni-koeln.de/id/eprint/46125


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