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

Abstract

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 $P[^{236}\mathrm{U}(d,\mathrm{pf})]/P[^{238}\mathrm{U}(d,\mathrm{pf})]$, which serves as a surrogate for the known cross section ratio of $^{236}\mathrm{U}(n,f)/^{238}\mathrm{U}(n,f)$. In addition, the $P[^{238}\mathrm{U}(d,{d}^{'}f)]/P[^{236}\mathrm{U}(d,{d}^{'}f)]$ ratio as a surrogate for the $^{237}\mathrm{U}(n,f)/^{235}\mathrm{U}(n,f)$ cross section ratio was measured for the first time in an unprecedented range of excitation energies.