Structure of neutron-rich Zn isotopes

A $\beta$-decay spectroscopy experiment in the closest vicinity of $^{78}$Ni was performed at RIBF as a part of the EURICA campaign. The low-lying level structure in odd-mass isotonic chain along the neutron magic number of $N=50$ is determined by the neutron single-particle evolution with decreasing proton number. Some reduction of the neutron single-particle energy gap between $2d_{5/2}$ and $3s_{1/2}$ orbitals was already indicated by the $\beta$-decay studies on $^{83}$Ge$_{32}$. Theoretical models, that have attempted to extend this evolution towards $^{78}$Ni, are not yet in agreement. We have performed the $\beta$-decay measurement of neutron-rich Cu isotopes in order to determine the low-lying level structure in Zn istopes which have only two valence protons above $^{78}$Ni. In this contribution, the newly constructed level schemes of $^{79-81}$Zn will be presented. The shell structure and its evolution based on the comparison with shell-model calculations will also be discussed.