Shell evolution beyond Z = 28 and N = 50: Spectroscopy of 81,82,83,84Zn

We report on the measurement of new low-lying states in the neutron-rich ^81,82,83,84Zn nuclei via in-beam γ-ray spectroscopy. These include the 4₁⁺ → 2₁⁺ transition in ⁸²Zn, the 2₁⁺ → 0_g.s.⁺ and 4₁⁺ → 2₁⁺ transitions in ⁸⁴Zn, and low-lying states in ^81,83Zn were observed for the first time. The reduced E ( 2₁⁺) energies and increased E (4₁⁺) / E (2⁺₁) ratios at N = 52, 54 compared to those in ⁸⁰Zn attest that the magicity is confined to the neutron number N = 50 only. The deduced level schemes are compared to three state-of-the-art shell model calculations and a good agreement is observed with all three calculations. The newly observed 2⁺ and 4⁺ levels in ⁸⁴Zn suggest the onset of deformation towards heavier Zn isotopes, which has been incorporated by taking into account the upper sdg orbitals in the Ni78-II and the PFSDG-U models.