Detailed γ-ray spectroscopy of55Crand56Cr:Confirmation of the subshell closure atN=32

The nuclei ${}^{55,56}\mathrm{Cr}$ were populated to high spin following the reaction ${}^{48}\mathrm{Ca}{(}^{11}\mathrm{B}{,pxn)}^{58-x}\mathrm{Cr}$ at a beam energy of 35–40 MeV. The level scheme of ${}^{55}\mathrm{Cr}$ has been confirmed and extended to $J^{\pi }={\frac{25}{2}}^{+}.$ The level scheme of ${}^{56}\mathrm{Cr}$ has been extended to $J=13.\mathrm{}$ The spins and parity of the majority of levels have been determined unambiguously for the first time. The first firm evidence for an intruder band based on the $\nu g_{9/2}$ orbital has been observed in ${}^{55}\mathrm{Cr}.$ In ${}^{56}\mathrm{Cr},$ the position of the first $4^{+}$ state has been determined unambiguously and the presence of a subshell closure at $N=32\mathrm{}$ has been confirmed on the basis of the $E_{4_1^{+}}{/E}_{2_1^{+}}$ systematics. The properties of both nuclei are compared with total Routhian surface calculations and with previous predictions of subshell closures at $N=32\mathrm{}$ and 34. The systematics in the region are discussed in terms of the strong $\nu f_{5/2}-\pi f_{7/2}$ interaction and its effect on the underlying single-particle structure.