Angular distributions of photofission of ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ have been measured using bremsstrahlung γ beams in the (5.4-6.4) MeV range. With decreasing energy below 6 MeV the angular anisotropy decreases strongly and, moreover, a shelf appears in the isotropic component of the yield. These effects are interpreted in terms of a competition between prompt and delayed fission. Vibrational resonances in the $1^{-0\mathrm{}}$ and $2^{+0\mathrm{}}$ channels are detected.

NUCLEAR REACTIONS, FISSION Angular distributions and yields of subthreshold photofission of ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ in the (5.4-6.4) MeV range.

• Received 18 September 1981

DOI:https://doi.org/10.1103/PhysRevC.24.2762