Experimental Evidence For Ni-56-Core Breaking From The Low-Spin Structure Of The N=Z Nucleus Cu-58(29)29

Low-spin states in the odd-odd N=Z nucleus Cu-58 were investigated with the Ni-58(p,ngamma)Cu-58 fusion evaporation reaction at the FN-TANDEM accelerator in Cologne. gammagamma-coincidences, gammagamma-angular correlations, and signs of gamma-ray polarizations were measured. Seventeen low-spin states below 3.6 MeV and 17 new transitions were observed. Ten multipole mixing ratios and 17 gamma-branching ratios were determined for the first time. New detailed spectroscopic information on the 2(2)(+) state, the isobaric analogue state (IAS) of the 2(1)(+),T=1 state of Ni-58, makes Cu-58 the heaviest odd-odd N=Z nucleus with known B(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 4(1)(+),T=1 state in Ni-58. 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 delta interaction. The role of the Ni-56 core excitations for the low-spin structure in Cu-58 is discussed.