The low-lying yrast states in the ${}^{51}\mathrm{Ca}$ and ${}^{52}\mathrm{Sc}$ nuclei were investigated to obtain information on the evolution of the $p_{1/2}$ and $f_{5/2}$ neutron single-particle orbitals in neutron-rich nuclei near proton number $Z=20$. Level structures associated with neutron excitations into these two orbitals and with proton excitations across the $Z=20$ shell gap were identified. Shell-model calculations with the recently proposed GXPF1A interaction account reasonably well for the $\mathit{fp}$-shell states. The energy separation between the $\nu p_{1/2}$ and $\nu f_{5/2}$ orbitals in the Ca isotopes appears to be overestimated by the GXPF1A Hamiltonian.

• Received 6 October 2007

DOI:https://doi.org/10.1103/PhysRevC.77.014304