First observation of excited states in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow/><mml:mrow><mml:mn>137</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">Te</mml:mi></mml:math>and the extent of octupole instability in the lanthanides

Excited states in ${}^{137}\mathrm{Te},$ populated in spontaneous fission of ${}^{248}\mathrm{Cm},$ were studied by means of prompt-$\ensuremath{\gamma}$ spectroscopy, using the EUROGAM2 multidetector array. This is the first observation of excited states in ${}^{137}\mathrm{Te}.$ The yrast excitations of ${}^{137}\mathrm{Te}$ are due to the three valence neutrons, occupying the $\ensuremath{\nu}{f}_{7/2}$ and $\ensuremath{\nu}{h}_{9/2}$ orbitals, similarly as observed in its heavier $N=85$ isotones. Systematic comparison of excited levels in the $N=85$ isotones shows inconsistencies in spin and parity assignments in ${}^{139}\mathrm{Xe}$ and ${}^{141}\mathrm{Ba}$ nuclei. The new data for ${}^{137}\mathrm{Te}$ do not confirm earlier suggestions that octupole correlations increase in the $N=85$ isotones, close to the $Z=50$ closed shell.

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