Further Evidence for Shape Coexistence in 79Znm near Doubly Magic 78Ni

Abstract

Isomers close to doubly magic 78 28Ni50 provide essential information on the shell evolution and shape coexistence near the Z ¼ 28 and N ¼ 50 double shell closure. We report the excitation energy measurement of the 1=2þ isomer in 79 30Zn49 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=2þ isomer at 942(10) keV, slightly below the 5=2þ 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 ¼ 49 isotones. The 1=2þ 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.