A fusion-evaporation reaction has been employed to search for isomeric states in the $N=77\mathrm{}$ isotope ${}_{63}^{140}\mathrm{Eu}$ 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 ${}^{140}\mathrm{Eu}.$ 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 $N=77\mathrm{}$ isotones. Within this framework, the isomer is interpreted to be built upon a $\pi h_{11/2}\otimes \nu h_{11/2}$ two-quasiparticle configuration.

• Received 9 April 2002

DOI:https://doi.org/10.1103/PhysRevC.66.034308