Experimental evidence for 56Ni-core breaking from the low-spin structure of the N = Z nucleus 2958Cu29

Abstract

Low-spin states in the odd-odd N = Z nucleus 58Cu were investigated with the 58Ni(p,nγ)58Cu fusion evaporation reaction at the FN-TANDEM accelerator in Cologne, γγ-coincidences, γγ-angular correlations, and signs of γ-ray polarizations were measured. Seventeen low-spin states below 3.6 MeV and 17 new transitions were observed. Ten multipole mixing ratios and 17 γ-branching ratios were determined for the first time. New detailed spectroscopic information on the 22+ state, the isobaric analogue state (IAS) of the 21+, T = 1 state of 58Ni, makes 58Cu the heaviest odd-odd N = Z nucleus with known 5(E2;2+, T = 1→0+,T = 1) value. The 4 + state at 2.751 MeV, observed here for the first time, is identified as the IAS of the 41+, T = 1 state in 58Ni. The new data are compared to full pf-shell-model calculations with the GXPF1 residual interaction and to calculations within a pf 5/2 configurational space with a residual surface δ interaction. The role of the 56Ni core excitations for the low-spin structure in 58Cu is discussed.