Shell quenching inNi78: A hint from the structure of neutron-rich copper isotopes

Abstract

Recent progress in experimental techniques allows us to study very exotic systems like neutron-rich nuclei in the vicinity of $^{78}\mathrm{Ni}$. The spectroscopy of this region can nowadays be studied theoretically in the large scale shell model calculations. In this work, we perform a shell model study of odd copper nuclei with $N=40--50$, in a large valence space with the $^{48}\mathrm{Ca}$ core, using a realistic interaction derived from the CD-Bonn potential. We present the crucial importance of the proton core excitations for the description of spectra and magnetic moments, which are for the first time correctly reproduced in theoretical calculations. Shell evolution from $^{68}\mathrm{Ni}$ to $^{78}\mathrm{Ni}$ is discussed in detail. A weakening of the $Z=28$ gap when approaching the $N=50$ shell closure, suggested by the experimental evidence, is confirmed in the calculations.