Yrast isomers in exotic [ital N]=81 nucleus [sup 151]Yb studied using a fragment mass analyzer

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