16.12.2015
Research news
Dissertation news

Dissertation: 17 Dec 2015 Detailed spectroscopy of the neutron-deficient bismuth isotopes 193,195Bi (Herzan)

Time:

17.12.2015 12:00 — 15:00


Location: Ylistonrinne, FYS1
M.Sc. Andrej Herzan defends his doctoral dissertation in Physics ”Detailed spectroscopy of the neurtron-deficient bismuth isotopes 193;195 Bi". Opponent Professor Filip Kondev (Argonne National Laboratory, USA) and custos Adjunct Professor Sakari Juutinen (University of Jyväskylä). The doctoral dissertation is held in English.

AndrejHerzannetti.jpgM.Sc. Andrej Herzan defends his doctoral dissertation in Physics ”Detailed spectroscopy of the neutron-deficient bismuth isotopes 193;195Bi". Opponent Professor Filip Kondev (Argonne National Laboratory, USA) and custos Adjunct Professor Sakari Juutinen (University of Jyväskylä). The doctoral dissertation is held in English.

Nuclear physics can be seen as a tool that allows the communication of Nature with us, people - observers, via the „encrypted“ language. This language may be considered as a set of physical quantities, variables, logically interconnected in mathematical expressions.

Nuclei of the present study are radioactive. Both the 193Bi and 195Bi isotopes have a half-life of approximately one minute, and hence the data collection must be fast and efficient. After their production in the experiments, they undergo complex de-excitation processes before reaching their ground states. 

The aim of the present study was to search for new structures in the neutron-deficient 193Bi and 195Bi isotopes, involved in the de-excitation of nuclei. The goal of the present work is now achieved by observing new high-spin isomeric states and several collective structures telling us that both nuclei can also exist in deformed shapes. We can imagine them as rotating disks, whereas both nuclei are sphere-like in their ground state. Hence, strong manifestation of shape coexistence is present in both isotopes. This means that both nuclei can change their shapes on their way from the excited state to a ground state. Moreover, it is found that 193Bi nuclei can even survive in the so-called superdeformed shape, similar to that of a fast rotating rugby ball. This observation truly makes the 193Bi isotope unique, since superdeformation has only been observed in very few isotopes of the chart of nuclei so far. It is even more exciting to have such nuclear features observed particularly in bismuth nuclei, because they are created by adding just one single proton to a semi-magic lead core.

The aforementioned observations provide a high-quality input data for theoretical models aiming to describe and explain systematic behaviour of nuclei, which can then have impact on different aspects of our lives. As in each area of the basic research, true potential of the present work shall be seen in the future. Nevertheless, surprising observations are made especially in 195Bi, which will certainly have a large impact on pursuing new discoveries in this mass region of the chart of nuclei.

The experimental results of the present study employing the state-of-the-art instrumentation represent the first-class research recognized worldwide.

The dissertation is published in the series Department of Physics Research number 10, 119 p., Jyväskylä 2015. ISSN: 0075-465X, ISBN: 978-951-39-6438-2 (print.), ISBN: 978-951-39-6439-9 (PDF.) It is available at the University Library’s Publications Unit, tel. +358 (0)40 805 3825, myynti@library.jyu.fi. or http://www.jyu.fi/static/fysiikka/vaitoskirjat/2015/Herzan-Andrej_2015

Abstract

Two experiments aiming to study the shape coexistence and competing structures in 193Bi and 195Bi isotopes have been performed at the Accelerator laboratory of the University of Jyväskylä, Finland (JYFL). Many new states have been found, hugely extending the previously known level schemes for both isotopes. The proton i13/2 bands were extended up to Iπ = 45/2+ in both the 193,195Bi isotopes. In case of 193Bi, the Iπ = 31/2+ member of the proton i13/2 band was found to de-excite also to a long-lived isomeric state. This link determines the energy of the isomeric state to be 2350(1) keV and suggests a spin and parity of 29/2+. The  half-life of the isomeric state was measured to be 85(3) µs. A level structure on top of this isomeric state was constructed. The newly observed 49 keV E2 transition provides a link between the (29/2-) isomeric state and lower-lying structures in 193Bi. A superdeformed band almost identical to that present in the neighbouring isotope 191Bi has been identified. Both the 29/2+ and (29/2-) isomeric states, together with the full decay-paths have also been identified in 195Bi. In both isotopes, the decay cascades from 31/2+ states to the 29/2+ isomeric states are surprisingly similar. Compared to 193Bi, measured half-lives of these isomeric states are considerably shorter in 195Bi. Experimental evidence is given proving the smaller quadrupole deformations in 195Bi when compared to 193Bi nucleus. Moreover, several new rotational collective structures have been identified in 195Bi, even though their variety is not as rich as in 193Bi. This is the first time the collective structures have been observed up to a high spins and excitation energies in 195Bi. Strong manifestation of shape coexistence is thus proved to be present also in 195Bi.

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Andrej Herzan

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andrej.a.herzan@jyu.fi