Shell evolution of N=40 isotones towards Ca-60: First spectroscopy of Ti-62

Abstract

Excited states in the N = 40 isotone Ti-62 were populated via the V-63( p, 2p)Ti-62 reaction at similar to 200MeV/nucleonat the Radioactive Isotope Beam Factory and studied using gamma-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-62 ground state. These energies are increased compared to the neighboring Cr-64 and Fe-66 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-62 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-60. (C) 2019 The Authors. Published by Elsevier B.V.