Rotational Bands in the Doubly Magic NucleusN56i

Structures of the medium- to high-spin states in the doubly magic nucleus ${}^{56}\mathrm{Ni}$ have been investigated using the reaction ${}^{28}\mathrm{Si}{(}^{36}\mathrm{Ar},2\mathrm{}\alpha )$ and the $\gamma$-ray spectrometer Gammasphere in conjunction with the $4\pi$ charged-particle detector array Microball. Two well-deformed rotational bands have been identified. There is evidence that one of the bands, which is identical to a sequence in the odd-odd neighbor ${}^{58}\mathrm{Cu}$, partially decays via proton emission into the ground state of ${}^{55}\mathrm{Co}$. Predictions of extensive large-scale shell-model and cranked Hartree-Fock and Hartree-Fock-Bogolyubov calculations are compared with the experimental data.