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The 50 � N,Z � 82 region of the Segrè chart, spanning the nuclei “northwest” of doubly-magic 132Sn, is an intriguing study ground to test the suitability and predictive power of nuclear models at both low and high spins. Low-spin excited states in the nearly spherical nuclei near proton- and neutronshell closures are well described as anharmonic vibrations [1] with a gradual change to rotational structures further away from the closed shells. Further on, quasiparticle excitations play a key role and are responsible for the presence of yrast-trap isomers. These long-lived states interrupt and fragment the decay flux in spectroscopic investigations. High-j couplings involving the unique-parity h11/2 neutron-hole orbital give rise to a wealth of high-spin states with multi-quasiparticle character. In particular, detailed knowledge of isomers is crucial to ascertain the active quasiparticle configurations in the specific nucleus.

Isomers in near-spherical Z=51, antimony isotopes are reported here for the first time using fusion-fission reactions between Al27 and a pulsed Hf178 beam of energy, 1150 MeV. γ rays were observed from the decay of isomeric states with half-lives, T1/2=200(30) and 52(3)μs, and angular momenta I=(252) and Iπ=232+, in Sb121,123, respectively. These states are proposed to correspond to ν(h112)2 configurations, coupled to an odd d52 or g72 proton. Nanosecond isomers were also identified at Iπ=192- [T1/2=8.5(5) ns] in Sb121 and Iπ=(152-) [T1/2=37(4) ns] in Sb123. Information on spins and parities of states in these nuclei was obtained using a combination of angular correlation and intensity-balance measurements. The configurations of states in these nuclei are discussed using a combination of spin/energy systematics and shell-model calculations for neighboring tin isotones and antimony isotopes.