Axial and triaxial degrees of freedom in 72Zn

S. Hellgartner, D. Mücher*, K. Wimmer*, V. Bildstein, J.L. Egido, R. Gernhäuser, R. Krücken, A.K. Nowak, M. Zielińska, C. Bauer, M.L.L. Benito, S. Bottoni, H. De Witte, J. Elseviers, D. Fedorov, F. Flavigny, A. Illana, M. Klintefjord, T. Kröll, R. LutterB. Marsh, R. Orlandi, J. Pakarinen, R. Raabe, E. Rapisarda, S. Reichert, P. Reiter, M. Scheck, M. Seidlitz, B. Siebeck, E. Siesling, T. Steinbach, T. Stora, M. Vermeulen, D. Voulot, N. Warr, F.J.C. Wenander

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

The unstable N = 42 nucleus 72Zn has been studied using multiple safe Coulomb excitation in inverse kinematics. The experiment was performed at the REX-ISOLDE facility at CERN making first use of the silicon detector array C-REX in combination with the γ-ray spectrometer Miniball. The high angular coverage of C-REX allowed to determine the reduced transition strengths for the decay of the yrast 0+1, 2+and 4+1 as well as of the
0+2 and 2+states in 72Zn. The quadrupole moments of the 2+1, 4+and
2+states were extracted. Using model independent quadrupole invariants, the ground state of 72Zn was found to have an average deformation in the γ degree of freedom close to maximum triaxiality. In comparison to experimental data in zinc isotopes with N < 40, the collectivity of the 4+state in neutron-rich 72Zn is significantly larger, indicating a collective yrast band based on the ground state of 72Zn. In contrast, a low experimental
B(E2;0+2 →2+1) strength was determined, indicating a different structure for the 0+2 state. Shell-model calculations propose a 0+2 state featuring a larger fraction of the (spherical) N = 40 closed-shell configuration in its wave function than for the 0+1 ground state.

The results were also compared with beyond mean field calculations which corroborate the large deformation in the γ degree of freedom, while pointing to a more deformed 0+state. These experimental and theoretical findings establish the importance of the γ degree of freedom in the ground state of 72Zn, located between the 68,70Ni nuclei that have spherical ground states, and 76Ge, which has a rigid triaxial shape.
Original languageEnglish
Article number137933
Number of pages8
JournalPhysics Letters B
Volume841
Early online date26 Apr 2023
DOIs
Publication statusPublished - 10 Jun 2023

Keywords

  • multiple Coulomb excitation
  • 72Zn
  • N = 40
  • sub-shell closure
  • triaxiality

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