Yrast isomers in exotic N=81 nucleus Yb151 studied using a fragment mass analyzer

Product recoils from the reaction 96Ru +255 MeV 58Ni → 154Hf* were analyzed using the Argonne Fragment Mass Analyzer and transported to a collector foil behind the focal plane, where decay of μs isomers could be studied under low background conditions. The recoils were dispersed in A/q as they traversed the position-sensitive focal-plane detector, and recoil–γ-ray coincidences could thus be used to assign masses for specific γ-ray cascades. By use of these methods, yrast isomers with half-lives of 2.6(7) μs and 20(1) μs have been firmly assigned to the exotic N=81 nucleus 151Yb, and the main features of the isomeric decays have been established. The yrast level structure of 151Yb and lighter N=81 isotones are compared.