Shell structure studies in the vicinity of the doubly-magic $^{78}$Ni by in-beam $\gamma$-ray spectroscopy

In-beam $\gamma$-ray spectroscopy in the vicinity of $^{78}$Ni is reported. In order to pin down the shell evolution on and beyond $N=50$ in neutron-rich nucleus, the energies of low-lying excited states in the isotopes around $^{78}$Ni were measured. The experiment was performed at the RIKEN Nishina Center for Accelerator-Based Science. The secondary beams of isotopes around $^{78}$Ni were produced by in-flight fission reactions of $345$ MeV/u ${}^{238}$U primary beam on a $925$ mg/cm${}^2$ beryllium target. The secondary beams then impinged on a $1889$ mg/cm${}^2$ thick beryllium target to produce the isotopes of interest. The de-excitation $\gamma$-rays were measured with the NaI(Tl) detector array DALI2 in coincidence with the reaction products which were analyzed in the ZeroDegree spectrometer. Doppler corrected $\gamma$-ray energy spectra obtained for the reaction residues Zn, Cu and Ni isotopes will be shown. The nuclear structure in this region will be discussed by the level scheme obtained, e.g. the vibrational mode in $^{80}$Zn, as well as the energy trends of the low-lying states in the isotope chains.