New effective interaction for $0\mathit{\hslash }\omega$ shell-model calculations in the $\mathit{sd}\text{−}\mathit{pf}$ valence space

The neutron-rich isotopes with $Z⩽20$, in particular those with neutron numbers around $N=28$, have been the focus of a lot experimental and theoretical scrutiny during the past few years. Shell-model calculations using the effective interaction SDPF-NR were able to predict or to explain most of the properties featured by these nuclei. Prominent among them is the disappearance of the $N=28$ shell closure for $Z⩽16$. We have incorporated into SDPF-NR some modifications, either on purely theoretical grounds or guided by new experimental information. The proposed interaction SDPF-U offers enhanced reliability with respect to the earlier version.

Figure 1

Effective neutron single-particle energies at $N=28$ from $Z=8$ to $Z=20$.

Figure 2

Effective proton single-particle energies in the calcium isotopes from $N=20$ to $N=40$.

Figure 3

Energy splitting (in MeV) between the lowest ${\frac{1}{2}}^{+}$ and ${\frac{3}{2}}^{+}$ states in the neutron-rich isotopes of potassium, chlorine, and phosphorus.