Competition of the Shell Closure and Deformations around the Doubly Magic 78Ni
R. Taniuchi · Progress of Theoretical and Experimental Physics · 2025
Abstract The properties of the neutron-rich isotope 78Ni, long postulated to be doubly magic, have been extensively explored through recent experimental and theoretical studies. Confirmations of robust shell closures at $Z=28$ and $N=50$ as well as hints of competing deformations in neighboring isotopes have been obtained. Innovations on the thick liquid hydrogen target system with vertex reconstructions and the in-beam $\gamma$-ray spectroscopy technique have facilitated detailed investigations into the nuclear structure of these extreme systems. Proton knockout reactions conducted at relativistic energies have provided the first experimental evidence of shape coexistence at the cornerstone nucleus 78Ni and its vicinity. As the nuclear structure around 78Ni influences the description of very neutron-rich systems and r-process nucleosynthesis, these findings underscore the importance of further investigations. This review encapsulates the recent results intensively studied at the Radioactive Isotope Beam Factory (RIBF) facility using the MINOS liquid hydrogen target system concerning the nuclear structure in the vicinity of 78Ni and the related theoretical developments. It outlines prospective research directions that could further illuminate this complex and intriguing area of the nuclear chart.