Detailed γ-ray spectroscopy of 55Cr and 56Cr:: Confirmation of the subshell closure at N=32 -: art. no. 034309

The nuclei Cr-55,Cr-56 were populated to high spin following the reaction Ca-48(B-11,pxn)Cr58-x at a beam energy of 35-40 MeV. The level scheme of Cr-55 has been confirmed and extended to J(pi)=25+/2. The level scheme of Cr-56 has been extended to J=13. 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 nug(9/2) orbital has been observed in Cr-55. In Cr-56, the position of the first 4(+) state has been determined unambiguously and the presence of a subshell closure at N = 32 has been confirmed on the basis of the E-41(+)/E-21(+) systematics. The properties of both nuclei are compared with total Routhian surface calculations and with previous predictions of subshell closures at N = 32 and 34. The systematics in the region are discussed in terms of the strong nuf(5/2)-pif(7/2) interaction and its effect on the underlying single-particle structure.