Two-hole structure outside Ni 78: Existence of a \u3bc s isomer of Co 76 and \u3b2 decay into Ni 76

In the EURICA campaign aimed at exploration of the Ni78 region, an isomeric state of Co76 has been observed via \u3b3-ray spectroscopy. The nuclei were produced by in-flight fission of a U238 beam at the Radioactive Isotope-Beam Factory. Two coincident \u3b3 rays of 192.02(30) and 446.4(7) keV from the decay of a t1/2=2.96(2529)\u3bcs 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+\u21922-)=1.79(16) 710-8 W.u. A \u3b2-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(57) 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+\u21926+) value of 0.786(5) W.u. A new excited state at 2994.6(5) keV, decaying via a \u3b3 ray of 2004.5(4) keV, has also been observed. This is in agreement with either of the predicted 02+ or 22+ states. These results are discussed in terms of the shell model and the interaction of the \u3bdp1/2 and \u3c0f7/2 orbitals. \ua9 2015 American Physical Society