Speaker
Description
In the region of N~50 several pieces of evidence supporting shape coexistence close to 78Ni have been found [1-3]. In particular, the ∼940-keV 1/2+ isomeric state in 79Zn, first observed in a (d,p) transfer measurement [4], has been interpreted as an intruder state, related to neutron excitations across N=50. Laser-spectroscopy measurements found a large isomeric shift for this state with respect to the 79Zn 9/2+ ground state indicating a significantly larger mean squared charge radius [2]. With the assumption of an axial quadrupole shape, this suggests a deformation of β=0.22, considerably larger than β=0.15 of the ground state. Indeed, the intruder structure in 79Zn has been attributed to a K=1/2 rotational band [3].
To probe the quadrupole collectivity of the 79Zn intruder states, we performed a Coulomb-excitation measurement with a post-accelerated 79Zn beam from HIE-ISOLDE that consisted of a mixture of nuclei in the 9/2+ ground state and the 1/2+ isomeric state, to populate excited states built on these two different configurations. In the experiment, γ rays were detected by the Miniball array [5], while scattered projectiles and beam recoils by an annular DSSD detector placed at forward angles.
The extracted quadrupole strengths from the Coulomb-excited transitions in the level scheme will be presented and compared with state-of-the-art shell model calculations. The implications of the results in the context of the shape coexistence around 78Ni will be discussed.
References
[1] A. Gottardo et al., Phys. Rev. Lett. 116, 182501 (2016)
[2] X. F. Yang et al., Phys. Rev. Lett. 116, 182502 (2016)
[3] L. Nies et al., Phys. Rev. Lett. 131, 222503 (2023)
[4] R. Orlandi et al., Phys. Lett. B 740, 298 (2015)
[5] N. Warr et al. ,Eur. Phys. J. A 49, 40 (2013)