Quenching of N = 28 shell gap and a low-lying quadrupole mode in the vicinity of neutron-rich N = 28 isotones

Abstract

We investigate the low-lying 2${}^{+}$ states of $N=28$ isotones (${}^{48}$Ca, ${}^{46}$Ar, ${}^{44}$S and ${}^{42}$Si) with using the canonical-basis time-dependent Hartree-Fock-Bogoliubov theory in which the pairing is taken into account self-consistently. The quadrupole mode with very small excitation energies emerges in ${}^{46}$Ar, ${}^{44}$S and ${}^{42}$Si due to the strong quadrupole correlations triggered by the quenching of the $N=28$ shell gap. The importance of the quadrupole correlations between the protons and neutrons, and the role of the pairing correlation to reinforce the lowest 2${}^{+}$ mode are discussed. It is also shown that the $B$(E2$\uparrow$) values of ${}^{48}$Ca and ${}^{46}$Ar are plausibly explained by our calculations.

Comments: Advances in Radioactive Isotope Science (ARIS2014) conference proceedings, 4 page, 2 figures