Benchmarking the External Surrogate Ratio Method using the (alpha,alpha'f) reaction at STARS

We measured the ratio of the fission probabilities of U-234* relative to U-236* formed via an (alpha,alpha') direct reactions using the STARS array at the 88-inch cyclotron at the Lawrence Berkeley National Laboratory. This ratio has a shape similar to the ratio of neutron capture probabilities from U-233(n,f) and U-235(n,f), indicating the alpha reactions likely formed a compound nucleus. This result indicates that the ratios of fission exit channel probabilities for two actinide nuclei populated via (a, a') can be used to determine an unknown fission cross section relative to a known one. The validity of the External Surrogate Ratio Method (ESRM) is tested and the results support the conclusions of Burke et al. [1].