Dissertation / PhD Thesis

GSI-2019-00456

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png γ-ray spectroscopy of $^{92,94}$Se isomeric decay

Lizarazo, C. Y. (Corresponding author) ; Pietralla, N. (Thesis advisor)

2018

Please use a persistent id in citations: urn:nbn:de:tuda-tuprints-72660

Abstract: The isomeric decay of 92,94Se has been studied by means of gamma-ray decay spectroscopy, in order to explore the nuclear structure of these very neutron-rich exotic nuclei far way from the ‘stability line’. The experiment was conducted in March 2015 at the Radioactive Ion Beam Factory of the RIKEN Nishina Center (RIBF-RIKEN) located in Japan. A radioactive beam of exotic nuclei was delivered by the BigRIPS fragment separator, tuned to select the desired products of the in-flight fission of a 238U primary beam on a Be target. This secondary beam impinged on a liquid Hydrogen (LH2) target, producing Selenium nuclei via different nucleon knock-out reactions. The final products passed through the ZeroDegree mass spectrometer, where they were identified on an event-by-event basis by means of determination of the proton number (Z) and mass-to-charge ratio (A/Q), and were finally implanted into a stack of silicon layers of the AIDA detector system. The existence and subsequent decay of isomeric excited states of these nuclei was studied with the EURICA gamma-ray HPGe detector placed around the AIDA layers. New spectroscopic information has been obtained for both isotopes, leading to an extension of their level schemes. In particular, the isomeric state of 94 Se has been observed for the first time. The possible causes of isomerism in these nuclei have been discussed and compared with the results, and it has been found that the presence of oblate-deformed quasi-particle states play an important role in the description of the isomerism phenomenon. The level schemes obtained have been compared with the predictions of different state-of-the-art beyond mean-field calculations, which propose all a prolate-to-oblate shape transition with increasing neutron number taking place between N=56 and N=60 (90,92,94 Se). Based on the observed structure of the level schemes and the deformation character of the isomeric states, the idea of a shape transition into an oblate structure at N=60 is supported.

Note: Dissertation, Technische Universitaet Darmstadt, 2018

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Contributing Institute(s):

1. Kernspektroskopie (KSP)

Research Program(s):

1. 612 - Cosmic Matter in the Laboratory (POF3-612) (POF3-612)
2. SUC-GSI-Darmstadt - Strategic university cooperation GSI-TU Darmstadt (SUC-GSI-DA) (SUC-GSI-DA)
3. HGS-HIRe - HGS-HIRe for FAIR (HGS-HIRe) (HGS-HIRe)

Appears in the scientific report 2018

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