Axial and triaxial degrees of freedom in 72Zn

The unstable N=42 nucleus 72Zn has been studied using multiple safe Coulomb excitation in inverse kinematics. experiment was performed at the REX-ISOLDE facility CERN making first use of silicon detector array C-REX combination with γ-ray spectrometer Miniball. high angular coverage allowed to determine reduced transition strengths for decay yrast 01+, 21+ and 41+ as well 02+ 22+ states 72Zn. quadrupole moments 21+, were extracted. Using model independent invariants, ground state found have an average deformation γ degree freedom close maximum triaxiality. In comparison experimental data zinc isotopes N<40, collectivity neutron-rich is significantly larger, indicating a collective band based on contrast, low B(E2;02+→21+) strength determined, different structure state. Shell-model calculations propose featuring larger fraction (spherical) N=40 closed-shell configuration its wave function than 01+ results also compared beyond mean field which corroborate large freedom, while pointing more deformed These theoretical findings establish importance 72Zn, located between 68,70Ni nuclei that spherical states, 76Ge, rigid triaxial shape.