Estimation of (n,f) cross sections by measuring reaction probability ratios

Neutron-induced reaction cross sections on unstable nuclei are inherently difficult to measure due to target activity and the low intensity of neutron beams. In an alternative approach, named the “surrogate” technique, one measures the decay probability of the same compound nucleus produced using a stable beam on a stable target to estimate the neutron-induced reaction cross section. As an extension of the surrogate method, in this paper we introduce a new technique of measuring the fission probabilities of two different compound nuclei as a ratio, which has the advantage of removing most of the systematic uncertainties. This method was benchmarked in this report by measuring the probability of deuteron-induced fission events in coincidence with protons, and forming the ratio P[²³⁶U(d,pf)]/P[²³⁸U(d,pf)], which serves as a surrogate for the known cross section ratio of ²³⁶U(n,f)/²³⁸U(n,f). In addition, the P[²³⁸U(d,d^'f)]/P[²³⁶U(d,d^'f)] ratio as a surrogate for the ²³⁷U(n,f)/²³⁵U(n,f) cross section ratio was measured for the first time in an unprecedented range of excitation energies.