Determining the average prompt-fission-neutron multiplicity for ${}^{239}$Pu($n$,$f$) via a ${}^{240}$Pu($\alpha$,${\alpha }^{\prime }f$) surrogate reaction

Abstract

The average prompt-fission-neutron multiplicity $\bar{\nu }$ is of significance in the areas of nuclear theory, nuclear nonproliferation, and nuclear energy. In this work, the surrogate-reaction method has been used for the first time to indirectly determine $\bar{\nu }$ for ${}^{239}$Pu($n$,$f$) via ${}^{240}$Pu($\alpha$,${\alpha }^{\prime }f$) reactions. A ${}^{240}$Pu target was bombarded with a beam of 53.9-MeV $\alpha$ particles. Scattered $\alpha$ particles, fission products, and neutrons were measured with the NeutronSTARS detector array. Values of $\bar{\nu }$ were obtained for a continuous range of equivalent incident neutron energies between 0.25--26.25~MeV, and the results agree well with direct neutron measurements.