The level structure of ${}_{}{}^{227}{}_{}{}^{}\mathrm{Th}$ has been studied using the electron capture decay of ${}_{}{}^{227}{}_{}{}^{}\mathrm{Pa}$ and the ${\mathrm{\beta }}^{\mathrm{-}}$ decay of ${}_{}{}^{227}{}_{}{}^{}\mathrm{Ac}$ to give a total of 20 levels where only four were previously known. This level structure then makes possible a more complete interpretation of the recently studied ${}_{}{}^{231}{}_{}{}^{}\mathrm{U}$ alpha decay into ${}_{}{}^{227}{}_{}{}^{}\mathrm{Th}$. The level structure can be interpreted using both strong coupling and intermediate coupling models in terms of K=1/$2^{\pm }$,K=3/$2^{\pm }$, and more tentative K=5/$2^{\pm }$ parity double bands which implies that ${}_{}{}^{227}{}_{}{}^{}\mathrm{Th}$ has reflection asymmetry. Futhermore, the detailed interpretation of the level structure of ${}_{}{}^{227}{}_{}{}^{}\mathrm{Th}$ solves the long standing problem of the ground state spin-parity of ${}_{}{}^{227}{}_{}{}^{}\mathrm{Th}$ which is shown to be 1/$2^{+}$.

• Received 1 November 1994

DOI:https://doi.org/10.1103/PhysRevC.51.1199