New decay scheme of the ${}_{51}{}^{136}\mathrm{Sb}_{85} 6^{-}$ isomer

We report new data on the ${}^{136}\mathrm{Sb}{6}^{-}$ yrast isomer with $T_{1/2}=489\left(40\right) \mathrm{ns}$ and $\pi g_{7/2}^1\times \nu f_{7/2}^3$ configuration, populated in the projectile fission of ${}^{238}\mathrm{U}$ on a ${}^9\mathrm{Be}$ target. The analysis confirms the lifetime, providing a good accuracy measurement. In addition, the decay of the isomer to the ground state is newly suggested. Our result for the isomeric decay scheme is in a good agreement with shell-model calculations.

Figure 1

The delayed and background-subtracted $\gamma$-ray spectrum for ${}^{136}\mathrm{Sb}$ (a). Lifetime fits and unsubtracted $\gamma$-ray spectrum for a short time window are shown in the insets. Coincidence-gate spectra on each of the transitions are plotted in (b), (c), and (d).

Figure 2

Revised experimental level scheme of the $6^{-}$ isomer in ${}^{136}\mathrm{Sb}$ compared to shell-model (SM) calculations.