Doubly Closed Shell of Nickel-78

Abstract

The doubly magic features of the very unstable nucleus located far from the stability line, ⁷⁸Ni, were investigated experimentally. To accomplish the measurement of this short-lived isotope, a new target and detector system was developed to measure the de-excitation gamma rays with a better Doppler reconstruction following proton-knockout reactions. While the high energy of the first excited state of ⁷⁸Ni corroborates its closed-shell nature, a second state was found at a similar excitation energy. This observation suggests a possible shape-coexisting nature in this nucleus and questions the nuclear shell robustness for isotopes further away from stability, where the nucleosynthesis is proposed to occur.