University of Jyväskylä

Dissertation: 12 Jan 2018: Probing the limits of existence and pancake-like shapes in lead and thallium nuclei (Badran)

Start date: Jan 12, 2018 12:00 PM

End date: Jan 12, 2018 03:00 PM

Location: Ylistönrinne, FYS1

Hussam BadranM.Sc. Hussam Badran defends his doctoral dissertation in Physics "Decay spectroscopy of the very neutron-deficient lead and thallium isotopes 178,179Pb and 179Tl". Opponent Professor John F Smith (School of Engineering University of West of Scotland, U.K.) and custos Dr. Juha Uusitalo (University of Jyväskylä). The doctoral dissertation is held in English.

More than 99% of the mass of visible matter in the universe is nuclear matter. Protons and neutrons are the building blocks of atomic nuclei. Nuclear physics studies the structure of nuclei-their formation, stability, shapes and decay modes.

The present doctoral thesis in the field of experimental nuclear physics is focused on the study of the very exotic isotopes of the elements lead and thallium. The nuclei studied are radioactive with very short half-lives ranging from a few hundreds of microseconds to hundreds of milliseconds. The studied isotopes are so exotic that they are not perceived in nature but are artificially produced in an accelerator laboratory by using fusion reactions. The results obtained in the present work are at the limit of current instrumentation and target technology given that the production and the spectroscopic studies of these nuclei are highly challenging.

The aim of the present study was to search for possible new phenomena in nuclear structure caused by the large excess of protons. The 178,179Pb nuclei studied are the most neutron-deficient lead isotopes known to date. An additional motivation of the present work was to search for new structure in the proton-unbound 179Tl isotope, which expected to have quantum states with very different shapes.

Lead is the heaviest element, that we know has a magic number of protons in the nucleus. The alpha decay of just four 178Pb nuclei, which has 30 neutrons less than the most abundant lead isotope, 208Pb has been measured. From this the two-proton separation energy has been calculated, showing that despite the extra binding from the magic number, the nucleus becomes unbound to proton emission. Understanding this competition between the Coulomb and strong forces in the nucleus is an essential ingredient in determining the limits of nuclear existence. In addition, the decay properties of the neighbouring odd-mass isotope 179Pb have been studied through alpha decay and alpha-gamma coincidences with greater accuracy. This allowed the structure of an exotic nucleus beyond the two proton-drip line to be identified. Finally, in 179Tl the presence of a long-lived state has been deduced for the first time following the observation of a cascade of gamma rays using the GREAT spectrometer. This new state has been interpreted as having an oblate-shape (pancake-like) whereas the ground state has a spherical shape, like a basketball.

Hussam Badran completed his Master’s Degree in Radiation Protection and Safety of Radioactive Sources from Damascus University, Syria in 2012. In 2013, he started his PhD working in the Nuclear Spectroscopy research group at the Department of Physics of the University of Jyväskylä.

The thesis has been published in the Department of Physics, University of Jyväskylä, Research Report No. 2/2018, ISSN 0075-465X, ISBN 978-951-39-7329-2 (paper version) and 978-951-39-7330-8 (electronic version) 
Link to the PDF version of the dissertation:

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Doctoral Student Hussam Badran, tohtorikoulutettava
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