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Gamma-ray Spectroscopy ofNeutron-rich 111 Mo, 85,87 Ge andSelf-Conjugate 88 Ru Far From Stability

Time: Tue 2021-06-15 16.00

Location: Live-streaming via Zoom:, (English)

Subject area: Physics, Atomic, Subatomic and Astrophysics

Doctoral student: Özge Aktas , Kärnfysik

Opponent: Dr. Augusto Machiavelli, Lawrence Berkeley National Laboratory

Supervisor: Professor Ayse Nyberg, Kärnfysik; Professor Bo Cederwall, Kärnfysik, Fysik

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The neutron-deficient self-conjugate (N=Z) nucleus 8844 Ru 44 was populatedvia the heavy ion fusion evaporation reaction 54 Fe( 36 Ar, 2n) 88 Ru in an ex-periment performed at the GANIL accelerator laboratory in France. Usingthe AGATA γ-ray spectrometer together with ancillary detectors, promptγ − γ − 2n coincidence and charge particle anticoincidence analysis was per-formed for the low-lying energy spectrum of 88 Ru. The results confirm thepreviously assigned γ-ray cascade and extend it to the 14 + level. The levelscheme is consistent with a deformed rotational system. However, the rota-tional frequency of the alignment of the valence nucleons has a significantlyhigher value than what is predicted by theoretical calculations performedwithout isoscalar neutron-proton pairing. By including isoscalar pairing, anagrement is obtained with the experimentally observed delayed rotationalalignment.Excited states in the neutron-rich nuclei 109 Mo and 111 Mo were studiedfollowing nucleon knock-out reactions. Seven γ-ray transitions, some of themin prompt mutual coincidence, were identified for the first time in 111 Mo usingthe DALI2 and MINOS detector systems at the BigRIPS and ZeroDegree elec-tromagnetic fragment separator at the RIBF, RIKEN, Japan. Total Routhiansurface (TRS) and Particle-Plus-Rotor calculations have been performed toinvestigate the predicted shape coexistence and its effect on the structure ofnuclei in this region of the nuclear chart. Following the results of the calcula-tions, theoretical level schemes are proposed for positive and negative paritystates and compared with the experimental findings.Gamma-ray transitions have been identified for the first time in the ex-tremely neutron-rich (N = Z + 25) nucleus 87 Ge following nucleon knockoutreactions studied at the RIBF, RIKEN, Japan. Previously unknown γ-raytransitions between excited states in 85 Ge were also observed and placed ina tentative level scheme. The results are compared with large-scale shell-model calculations and potential energy surface calculations based on thetotal Routhian surface formalism. The neutron-rich titanium isotopes havebeen studied, and preliminary results are presented in this work. For the odd-even 57,59,61 Ti isotopes several gamma-ray transitions has been identified forthe first time. For the even-even isotopes 56,58,60 Ti the previously knowndecays from 2 + and 4 + spin-parity states, are confirmed with the currentpreliminary analysis.