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Abstract

Isomers close to doubly magic ₂₈⁷⁸Ni₅₀ provide essential information on the shell evolution and shape coexistence near the Z=28 and N=50 double shell closure. We report the excitation energy measurement of the 1/2⁺ isomer in ₃₀⁷⁹Zn₄₉ through independent high-precision mass measurements with the JYFLTRAP double Penning trap and with the ISOLTRAP multi-reflection time-of-flight mass spectrometer. We unambiguously place the 1/2⁺ isomer at 942(10) keV, slightly below the 5/2⁺ state at 983(3) keV. With the use of state-of-the-art shell-model diagonalizations, complemented with discrete nonorthogonal shell-model calculations which are used here for the first time to interpret shape coexistence, we find low-lying deformed intruder states, similar to other N=49 isotones. The 1/2⁺ isomer is interpreted as the bandhead of a low-lying deformed structure akin to a predicted low-lying deformed band in ⁸⁰Zn, and points to shape coexistence in ^79,80Zn similar to the one observed in ⁷⁸Ni. The results make a strong case for confirming the claim of shape coexistence in this key region of the nuclear chart.