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 0₁+, 2₁+ and 4₁+ as well as of the 0₂+ and 2₂+ states in ⁷²Zn. The quadrupole moments of the 2₁+, 4₁+ and 2₂+ 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 4₁+ 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;0₂+→2₁+) strength was determined, indicating a different structure for the 0₂+ state. Shell-model calculations propose a 0₂+ state featuring a larger fraction of the (spherical) N=40 closed-shell configuration in its wave function than for the 0₁+ 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 02+ 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.

Axial and triaxial degrees of freedom in ⁷²Zn / S. Hellgartner, D. Mucher, K. Wimmer, V. Bildstein, J.L. Egido, R. Gernhauser, R. Krucken, A.K. Nowak, M. Zielinska, C. Bauer, M.L.L. Benito, S. Bottoni, H. De Witte, J. Elseviers, D. Fedorov, F. Flavigny, A. Illana, M. Klintefjord, T. Kroll, R. Lutter, B. 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. - In: PHYSICS LETTERS. SECTION B. - ISSN 0370-2693. - 841:(2023 Jun), pp. 137933.1-137933.8. [10.1016/j.physletb.2023.137933]

Axial and triaxial degrees of freedom in ⁷²Zn

S. Bottoni;
2023

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 0₁+, 2₁+ and 4₁+ as well as of the 0₂+ and 2₂+ states in ⁷²Zn. The quadrupole moments of the 2₁+, 4₁+ and 2₂+ 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 4₁+ 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;0₂+→2₁+) strength was determined, indicating a different structure for the 0₂+ state. Shell-model calculations propose a 0₂+ state featuring a larger fraction of the (spherical) N=40 closed-shell configuration in its wave function than for the 0₁+ 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 02+ 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.
⁷²Zn; Multiple Coulomb excitation; N=40 sub-shell closure; Triaxiality
Settore FIS/04 - Fisica Nucleare e Subnucleare
giu-2023
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/971458
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