Search for proton emission of the isomeric $$mathbf {10^+}$$10+ state in $$mathbf {^{54}}$$54 Ni

Several experiments were conducted at the 10 MV Van-de-Graaff tandem accelerator at the Institute of Nuclear Physics, Cologne, to detect proton emission from the isomeric 6457-keV $$10^+$$ state in $$^{54}\hbox {Ni}$$. Excitation functions for two fusion–evaporation reactions were measured to maximise the population of the rare two-neutron evaporation channel from a $$^{56}\hbox {Ni}$$ compound nucleus. The search for delayed proton emission was based on the $$^{28}\hbox {Si}$$($$^{28}\hbox {Si},2n$$)$$^{54}\hbox {Ni}$$ reaction at a beam energy of 70 MeV. For this reaction, a cross-section limit for the population of the $$10^+$$ state in $$^{54}\hbox {Ni}$$ and its proton-decay branch was determined to be $$\sigma < 22$$ nb.