Excited states in the proton-unbound nucleus ${}^{109}\mathrm{I}$ were populated using the ${}^{54}\mathrm{Fe}{(}^{58}\mathrm{Ni},p2n)$ reaction at a beam energy of 220 MeV. Gamma rays in ${}^{109}\mathrm{I}$ were identified using the recoil-decay tagging technique. The analysis of proton-correlated $\gamma \gamma$ coincidence data produced the yrast decay sequence in ${}^{109}\mathrm{I}$, which can be tentatively assigned as built on the $h_{11/2}$ proton state based on systematic trends in the neighboring isotopes. This sequence is completely different from that reported previously. A comparison of the $h_{11/2}$ band $\mathrm{in}{\hspace{0.5em}}^{109}\mathrm{I}$ with those in heavier iodines shows that ${}^{109}\mathrm{I}$ continues the trend of decreasing quadrupole deformation with decreasing neutron number.

• Received 11 December 1998

DOI:https://doi.org/10.1103/PhysRevC.59.R1834