Two $\alpha$-decaying isomeric states were observed in ${}^{191}\mathrm{Po}$ with $E_{\alpha }=7334\mathrm{}\left(10\right)\mathrm{keV}$ and $\mathrm{T}{}_{1/2}=22\mathrm{}\left(1\right)\mathrm{ms}$ for ${}^{191g}\mathrm{Po}$ and $\mathrm{E}{}_{\alpha }=7378\mathrm{}\left(10\right)\mathrm{keV}$ and $\mathrm{T}{}_{1/2}=98\mathrm{}\left(8\right)\mathrm{ms}$ for ${}^{191m}\mathrm{Po}$. Evidence was found for fine-structure decay to excited levels in the ${}^{187}\mathrm{Pb}$ daughter nucleus. The tentative interpretation of these new levels involves the weak coupling of the odd neutron to an intruder $\pi \left(2p-2h\right)$ deformed $0^{+}$ state in the even-even core. The long half-life of the ${}^{191m}\mathrm{Po}$ $(\Delta l=0\mathrm{})$ $\alpha$ decay points to a deformed ${13/2}^{+}$ isomeric state in ${}^{191}\mathrm{Po}$.

• Received 17 November 1998

DOI:https://doi.org/10.1103/PhysRevLett.82.1819