Detailed γ-ray spectroscopy of <sup>55</sup> Cr and <sup>56</sup> Cr: Confirmation of the subshell closure at N=32
Appelbe DE., Barton CJ., Muikku MH., Simpson J., Warner DD., Beausang CW., Caprio MA., Cooper JR., Novak JR., Zamfir NV., Austin RAE., Cameron JA., Malcolmson C., Waddington JC., Xu FR.
The nuclei 55,56 Cr were populated to high spin following the reaction 48 Ca( 11 B,pxn) 58-x Cr at a beam energy of 35-40 MeV. The level scheme of 55 Cr has been confirmed and extended to J π =25/2 + . The level scheme of 56 Cr 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 νg 9/2 orbital has been observed in 55 Cr. In 56 Cr, 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 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 and 34. The systematics in the region are discussed in terms of the strong νf 5/2 -πf 7/2 interaction and its effect on the underlying single-particle structure.