Two-hole structure outside Ni78: Existence of a μs isomer of Co76 and β decay into Ni76

International audience; In the EURICA campaign aimed at exploration of the Ni78 region, an isomeric state of Co76 has been observed via γ-ray spectroscopy. The nuclei were produced by in-flight fission of a U238 beam at the Radioactive Isotope-Beam Factory. Two coincident γ rays of 192.02(30) and 446.4(7) keV from the decay of a t1/2=2.96(2925)μs isomeric state of Co76 have been observed. The decay of the isomer was assigned to an E1 transition with a reduced transition probability of B(E1;3+→2−)=1.79(16)×10−8 W.u. A β-decaying state with spin-parity 1− and a half-life of 16(4) ms was also observed in the data, and the known state with a half-life of 22(75) ms was assigned to have a spin-parity of 8−. Furthermore, the isomer of Ni76 has been remeasured to 547.8(33) ns giving a B(E2;8+→6+) value of 0.786(5) W.u. A new excited state at 2994.6(5) keV, decaying via a γ ray of 2004.5(4) keV, has also been observed. This is in agreement with either of the predicted 0+2 or 2+2 states. These results are discussed in terms of the shell model and the interaction of the νp1/2 and πf7/2 orbitals.