Shell evolution of $N=40$ isotones towards $^{60}$Ca: First spectroscopy of $^{62}$Ti

TL;DR

This study reports the first spectroscopy of $^{62}$Ti, revealing a deformed ground state and providing insights into shell evolution near $N=40$, with results supporting an extended island of inversion down to $Z=20$.

Contribution

First experimental spectroscopy of $^{62}$Ti, showing a deformed ground state and informing shell evolution and the extent of the island of inversion near $N=40$.

Findings

$^{62}$Ti has a deformed ground state.

Shell-model calculations reproduce the energies.

$^{60}$Ca is unlikely to be doubly magic.

Abstract

Excited states in the $N=40$ isotone $^{62}$Ti were populated via the $^{63}$V$(p,2p)$$^{62}$Ti reaction at $\sim$200~MeV/u at the Radioactive Isotope Beam Factory and studied using $\gamma$-ray spectroscopy. The energies of the $2^+_1 \rightarrow 0^{+}_{\mathrm{gs}}$ and $4^+_1 \rightarrow 2^+_1$ transitions, observed here for the first time, indicate a deformed $^{62}$Ti ground state. These energies are increased compared to the neighboring $^{64}$Cr and $^{66}$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 $^{62}$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 $^{60}$Ca.