Experimental Studies of the Neutron Deficient Atomic Nuclei 94Ru, 95Rh and 172Pt via their Electromagnetic Properties
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Time: Thu 2020-04-23 14.00
Subject area: Physics, Atomic, Subatomic and Astrophysics
Doctoral student: Aysegul Ertoprak , Fysik
Opponent: Professor Paul Garrett, University of Guelph, Department of Physics, 50 Stone Road E. Guelph, Ontario, Canada
Supervisor: Professor Bo Cederwall, Kärnfysik, Fysik
This thesis reports new results obtained from studies of the neutron deficient atomic nuclei 94Ru, 95Rh and 172Pt using two different experimental set-ups. In the first part, lifetimes of highly excited states in nuclei near the N=50 closed-shell (94Ru and 95Rh) were deduced from an analysis of the Doppler broadened transition lineshapes measured following the 58Ni(40Ca,4p) and 58Ni(40Ca,3p) fusion-evaporation reactions at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator complex situated in Caen, France. Doppler Shift Attenuation Method (DSAM) lifetime analysis was performed on the Doppler broadened peaks in energy spectra from γ-rays emitted from excited states in the nuclei of interest while they were slowing down in a thick 6 mg/cm2 metallic 58Ni target. For 94Ru, eight excited-state lifetimes in the angular momentum range I= (13-20)h have been measured in total, five of which were determined for the first time. For the lifetime analysis of 95Rh, three lifetime values have been obtained. One of them, the lifetime of the 39/21- excited state, has been measured for the first time. In the other cases, the lifetimes of the previously measured 29/22- and 37/21- excited states have been obtained. The corresponding B(M1) and B(E2) reduced transition strengths have been deduced and are discussed within the framework of large-scale shell model (LSSM) calculations. In the second part, the extremely neutron deficient 172Pt nucleus has been studied. Excited states in 172Pt were populated using the 96Ru(78Kr,2p) and 92Mo(83Kr,3n) reactions at the Accelerator Laboratory of the University of Jyväskylä (JYFL), Finland. Prompt γ-rays were detected using the JUROGAM high-purity germanium detector array at the target position while the identification and decay spectroscopy of 172Pt was performed using the RITU gas-filled separator in conjunction with the GREAT spectrometer. The Recoil Decay Tagging (RDT) technique was used for the selection of prompt γ-rays. The known positive-parity band has been extended and the negative-parity structure has been established on top of the lowest member of the negative parity band which has now been firmly assigned as spin-parity 3-. Moreover, the newly observed E3 transition provides a link between the negative parity band with the ground state. The observations of this E3 transition together with several E1 transitions connecting the negative-parity structure with the ground-state band is consistent with the presence of octupole collectivity in 172Pt. Furthermore, this is the first observation of an E3 transition connecting the negative parity band with the ground-state band in the Pt-Os-W region. The experimental results were interpreted in terms of LSSM and total routhian surface calculations. With the support of these theoretical calculations, evidence for octupole collectivity in 172Pt is proposed.