Seniority, collectivity, and $B(E2)$ enhancement in $^{72}$Ni

Gamma rays assigned to $_{28}^{72}$Ni$_{44}$\ have been identified with Gammasphere in deep-inelastic reactions involving a 450-MeV $^{76}$Ge beam and a $^{198}$Pt 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 $8^{+}\rightarrow6^{+}$ transition. These $\gamma$-ray coincidences were 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 $\nu=4,$ $6^{+}$ level that is depressed by the same two-body interaction responsible for the rather low 1095-keV $2_{1}^{+}$ energy, as compared to the valence-symmetry counterpart $_{44}^{94}$Ru$_{50}$.