Prompt Proton Decay of a Well-deformed Rotational Band in 58Cu

An excited well-deformed rotational band has been observed in the N = Z odd-odd nucleus Cu-58. The first excited state in this band decays via gamma emission to the spherical states associated with the first minimum in the potential, thus providing for its unambiguous assignment to Cu-58. I, contrast, its bandhead decays via emission of a prompt 2.4(1) MeV proton to an excited state in the daughter nucleus Ni-57. This is the first observation of proton decay from states associated with a deformed secondary minimum in the potential. Self-consistent Hartree-Fock calculations reproduce well both the large collectivity of this band and the general trend of its moment of inertia.