Measurement and Interpretation ofΓnΓffor Actinide Nuclei

The (${}_{}{}^3{}_{}{}^{}\mathrm{He}$, $\mathrm{df}$) and (${}_{}{}^3{}_{}{}^{}\mathrm{He}$, $\mathrm{tf}$) reactions were used to measure fission probabilities from threshold up to ∼ 12 MeV of excitation energy for a series of actinide nuclei. The data were fitted over the whole range of nuclei and excitation energies with a microscopic model which does not contain an arbitrary normalization for $\frac{{\Gamma }_n}{{\Gamma }_f}$. The fits indicate that for most actinide nuclei fission proceeds through a first saddle point that is not axially symmetric.