This work reports on the first observation of excited levels in the ${}^{139}\mathrm{I}$ nucleus. Levels in ${}^{139}\mathrm{I},$ populated in spontaneous fission of ${}^{248}\mathrm{Cm},$ were studied by means of prompt $\gamma$-ray spectroscopy, using the EUROGAM2 array. The level scheme of ${}^{139}\mathrm{I}$ obtained in this work shows patterns characteristic of a spherical vibrator, which result from a weak interaction of the ${}^{138}\mathrm{Te}$ core with the odd proton. No signs of octupole correlations were observed in ${}^{139}\mathrm{I}.$ The new data allow, for the first time systematic predictions to be made of energies and spins of states in the ${}^{137}\mathrm{Sb}$ nucleus, helping the future studies of the r-process nuclei at the $Z=50\mathrm{}$ line.

• Received 17 September 2001

DOI:https://doi.org/10.1103/PhysRevC.65.024307