First Evidence of Axial Shape Asymmetry and Configuration Coexistence in 74Zn: Suggestion for a Northern Extension of the N=40 Island of Inversion

The excited states of N = 44 74Zn were investigated via gamma-ray spectroscopy following 74Cu beta decay. By exploiting gamma-gamma angular correlation analysis, the 2 thorn 2 , 3 thorn 1 , 0 thorn 2 , and 2 thorn 3 states in 74Zn were firmly established. The gamma-ray branching and E2/M 1 mixing ratios for transitions deexciting the 2 thorn 2 , 3 thorn 1 , and 2 thorn 3 states were measured, allowing for the extraction of relative BoE2 thorn values. In particular, the 2 thorn 3 -0 thorn 2 and 2 thorn 3 -4 thorn 1 transitions were observed for the first time. The results show excellent agreement with new microscopic large-scale shell-model calculations, and are discussed in terms of underlying shapes, as well as the role of neutron excitations across the N = 40 gap. Enhanced axial shape asymmetry (triaxiality) is suggested to characterize 74Zn in its ground state. Furthermore, an excited K = 0 band with a significantly larger softness in its shape is identified. A shore of the N = 40 island of inversion appears to manifest above Z = 26, previously thought as its northern limit in the chart of the nuclides.

Automated summary

The excited states of N = 44 74Zn were investigated using gamma-ray spectroscopy, and different states were identified. The branching ratios and mixing ratios were measured for the transitions, allowing for the extraction of relative BOE2 thorn values. Some transitions were observed for the first time, and the results showed excellent agreement with theoretical calculations. The results were discussed in terms of shapes and neutron excitations.