Identification Of Excited States In Doubly Odd Eu-140(63)77 By Recoil-Isomer Tagging

A fusion-evaporation reaction has been employed to search for isomeric states in the N=77 isotope Eu-140(63) near the proton-drip line. The recoiling nuclei were implanted into a silicon detector, at the focal plane of a gas-filled separator, where prompt and delayed gamma-ray transitions were correlated across isomeric states using recoil-isomer tagging. The feeding and decay of a new 299(3) ns isomeric state was established. This measurement represents the first observation of excited high-spin states in Eu-140. The behavior of the new states above the isomer is discussed in terms of theoretical calculations based upon the cranked-shell model and upon the experimental systematics of other N=77 isotones. Within this framework, the isomer is interpreted to be built upon a pih(11/2)circle timesnuh(11/2) two-quasiparticle configuration.