Yrast Excitations around Doubly Magic {sup {bold 132}}Sn from Fission Product {bold {gamma}}-Ray Studies

Prompt {gamma}-ray cascades in neutron-rich nuclei around doubly magic {sup 132}Sn have been studied at Eurogam II using a {sup 248}Cm fission source. Yrast states to above 5.5 MeV in the two- and three-proton {ital N}=82 isotones {sup 134}Te and {sup 135}I are reported. They are interpreted in terms of valence proton and particle-hole core excitations with the help of shell model calculations employing empirical nucleon-nucleon interactions from both {sup 132}Sn and {sup 208}Pb regions. A serious inconsistency in the accepted masses of {ital N}=82 isotones near {sup 132}Sn is discovered but not resolved. {copyright} {ital 1996 The American Physical Society.}