Seniority, collectivity, and B(E2) enhancement in 72Ni

Gamma rays assigned to 2872Ni44 have been identified with Gammasphere in deep-inelastic reactions involving a 450-MeV 76Ge beam and a 198Pt target. Using a combination of spectra produced by double gates on the known 454-, 843-, and 1095-keV members of the ground-state cascade, a coincident line at 199 keV has been identified and is tentatively assigned as the 8+→6+ transition. These γ-ray coincidences have been observed only in prompt events, indicating an 8+ half-life below 20 ns and requiring a large B(E2) enhancement compared to that expected from a seniority scheme. This value is consistent with models showing decay to a seniority ν=4, 6+ level that is depressed by the same two-body interaction responsible for the rather low 1095-keV 21+ energy, as compared to the valence-symmetry counterpart 4494Ru50.