Low energy structure of even-even Ni isotopes close to 78Ni

The structure of magic neutron-rich nickel isotopes produced in the fragmentation of a 140AMeV86Kr beam was investigated. For the first time four gamma transitions were assigned to the decay of the Iπ=8+, T1/2=590−110+180ns isomer, thus establishing the 0+-2+-4+-6+-8+ ground-state band in 76Ni. The previously unknown 2+ and 4+ levels belonging to the ground-state band in 74Ni were identified in the β decay of 74Co (T1/2=30(3)ms). The decay properties of 72Co → 72Ni were verified and confirmed on the basis of γ-γ coincidence data. The relevance of the measured level properties for the magicity of 78Ni is analyzed with the help of advanced shell-model predictions.