1. Axial and triaxial degrees of freedom in Zn
- Author
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Hellgartner, S., Mücher, D., Wimmer, K., Bildstein, V., Egido, J.L., Gernhäuser, R., Krücken, R., Nowak, A.K., Zielińska, M., Bauer, C., Benito, M.L.L., Bottoni, S., De Witte, H., Elseviers, J., Fedorov, D., Flavigny, F., Illana, A., Klintefjord, M., Kröll, T., Lutter, R., Marsh, B., Orlandi, R., Pakarinen, J., Raabe, R., Rapisarda, E., Reichert, S., Reiter, P., Scheck, M., Seidlitz, M., Siebeck, B., Siesling, E., Steinbach, T., Stora, T., Vermeulen, M., Voulot, D., Warr, N., and Wenander, F.J.C.
- Abstract
The unstable N=42 nucleus $^{72}$Zn 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 $^{72}$Zn. The quadrupole moments of the 21+, 41+ and 22+ states were extracted. Using model independent quadrupole invariants, the ground state of $^{72}$Zn 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 $^{72}$Zn is significantly larger, indicating a collective yrast band based on the ground state of $^{72}$Zn. 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 $^{72}$Zn, located between the $^{68,70}$Ni nuclei that have spherical ground states, and $^{76}$Ge, which has a rigid triaxial shape.
- Published
- 2023