Symmetry breaking in mirror nuclei 55Co and 55Ni

Yrast states in mirror nuclei 55Co and 55Ni have been populated with a radioactive ion beam using the isotope separator on-line method. A shielded array of 7 compton suppressed germanium detectors recorded reaction gamma-rays. For channel selection, an array of 128 independent silicon detectors was used to differentiate exit channels with different number of proton and alpha particles emitted. From gamma-gamma and gamma-particle coincidences, three lines in 55Co and one line in 55Ni was obtained for the first time