Nearly degenerate isomeric states of $^{75}$Cu

The decays of two isomeric states in the neutron-rich nucleus Cu-75 have been studied via delayed gamma-ray spectroscopy. These states were populated by the fragmentation of a 60.4 A MeV Kr-86 primary beam, which impinged on a Be target at the LISE2k spectrometer of GANIL. Isomeric half-lives and branching ratios were measured, and a gamma-gamma coincidence analysis performed. These have allowed a revised level scheme of Cu-75 to be proposed. A comparison with large-scale shell-model calculations using different effective interactions and valence spaces shows the importance of proton excitations across the Z = 28 shell gap for reproducing the energy spacing between the isomeric states. The coexisting collective and single-particle properties of the (1/2(-)) and (3/2(-)) states, respectively, are similar to those of the same states in the neighboring Cu-69,Cu-71,Cu-73. The small energy spacings between the (1/2(-)), (3/2(-)), and 5/2(-) states are responsible for the isomerism.