Speaker
Description
Investigating nuclear structure, especially nuclear shells and their associated magic numbers, has been an important field of research in the last decades. Such proton and neutron numbers are associated with sudden changes in nuclear observables between neighboring isotopes, such as binding energies, charge radii, transition strengths, etc. With $N=50$ neutrons and $Z=28$ protons, the $^{78}$Ni nucleus at the crossroads at two magic numbers is a prime candidate to test our understanding of the shell model [1]. Furthermore, the effect of shape coexistence, i.e. the existence of spherical ground states and deformed excited states, is often found in nuclei where intruder states across shell gaps lead to a large amount of deformation [2], indicating nearby magicity. Indication for shape coexistence in $^{79}$Zn with $N=49$ and $Z=30$ has previously been found through laser spectroscopy experiments [3] and in $^{80}$Ga with $N=49$ and $Z=31$ through electron-conversion spectroscopy [4]. The latter, however, was disproven in follow-up experiments [5,6]. In this contribution, we present further evidence for shape coexistence in $^{79}$Zn through the first direct excitation energy measurements of the ½+ isomeric state using Penning trap and multi-reflection time-of-flight mass spectrometry, firmly establishing the ½+ and 5/2+ state ordering [7]. Utilizing discrete nonorthogonal shell model calculations, we find low-lying deformed intruder states, similar to other $N=49$ isotones, and investigate similarities in shapes between excited states in $^{79,80}$Zn and $^{78}$Ni.
[1] R. Taniuchi et al., Nature (London) 569, 53 (2019).
[2] Garrett, Zielińska, and Clement, Prog. Part. Nucl. Phys. 124, 103931 (2022)
[3] Yang et al., PRL 116, 182502 (2016)
[4] Gottardo et al., PRL 116, 182501 (2016)
[5] Garcia et al., PRL 125, 172501 (2020)
[6] S. Sekal et al., Phys. Rev. C 104, 024317 (2021).
[7] Nies et al., PRL 131, 222503 (2023)
