Speaker
Description
Shell evolution for the N=40 isotones has recently attracted considerable attention. In a single-particle shell model N=40, which corresponds to the filling of the $fp$ neutron shells, is predicted to be a sub-shell closure. However, measurements of the first 2$^+$ states in $^{64}$Cr and $^{66}$Fe give evidence of a rapid weakening of the N=40 gap when removing protons from the $f_{7/2}$ shell. Conversely, the 2$^+$ energies of $^{58,60}$Ti show only a slight decrease towards N = 40. To further understand the shell evolution towards the supposedly doubly-magic $^{60}$Ca, we report on the measurement of the first excited 2$^+$ state of $^{62}$Ti.
Excited states in $^{62}$Ti were populated via the $^{63}$V(p,p2)$^{62}$Ti reaction and studied using $\gamma$-ray spectroscopy. The energies of the 2$^{+}\rightarrow 0^+$ and 4$^{+}\rightarrow 2^+$ transitions, observed here for the first time, indicate a deformed $^{62}$Ti ground state. These energies are increased compared to the neighboring Cr and Fe isotones, suggesting a small decrease of quadrupole collectivity. This result 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 them. 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 island of inversion extends down to Z=20, disfavoring a possible doubly magic character of $^{60}$Ca.
