The orbital $M1$ scissors resonance has been measured for the first time in the quasicontinuum of actinides. Particle-$\gamma$ coincidences are recorded with deuteron and ${}^3\mathrm{He}$-induced reactions on ${}^{232}\mathrm{Th}$. The residual nuclei ${}^{231,232,233}\mathrm{Th}$ and ${}^{232,233}\mathrm{Pa}$ show an unexpectedly strong integrated strength of $B_{M1}=11–15{\mu }_n^2$ in the $E_{\gamma }=1.0–3.5\mathrm{MeV}$ region. The increased $\gamma$-decay probability in actinides due to scissors resonance is important for cross-section calculations for future fuel cycles of fast nuclear reactors and may also have an impact on stellar nucleosynthesis.

• Received 15 June 2012

DOI:https://doi.org/10.1103/PhysRevLett.109.162503