D ec 2 01 9 Shell evolution of N = 40 isotones towards 60 Ca : First spectroscopy of 62 Ti

Excited states in the N = 40 isotone Ti were populated via the V(p, 2p)Ti reaction at ∼200 MeV/nucleon at the Radioactive Isotope Beam Factory and studied using γ-ray spectroscopy. The energies of the 2+1 → 0 + gs and 4 + 1 → 2 + 1 transitions, observed here for the first time, indicate a deformed Ti ground state. These energies are increased compared to the neighboring Cr and Fe isotones, suggesting a small decrease of quadrupole collectivity. The present measurement is well reproduced by large-scale shell-model calculations based on effective interactions, while ab initio and beyond mean-field calculations do not yet reproduce our findings. The shell-model calculations for Ti show a dominant configuration with four neutrons excited across the N = 40 gap. Likewise, they indicate that the N = 40 island of inversion extends down to Z = 20, disfavoring a possible doubly magic character of the elusive Ca.