Decay Study of 257Rf

The isotope 257Rf was produced in the fusion‐evaporation reaction 208Pb (50Ti, n) 257Rf. Reaction products were separated by the Argonne Fragment Mass Analyzer. Radioactive decay and spontaneous fission of 257Rf and its decay products were investigated. An isomeric state in 257Rf, with a half‐life of 160−3142 μS, was discovered by detecting internal conversion electrons followed by alpha decays. It is interpreted as a three‐quasiparticle high‐K isomer. A second group of internal‐conversion electrons which were succeeded by alpha decay, with a half‐life of 4.1−1.3+2.4 s, was observed. These events might originate from the decay of excited states in 257Lr, populated by electron‐capture decay of 257Rf, or from another isomer in 257Rf.