Determining the average prompt-fission-neutron multiplicity for Pu-239(n, f) via a Pu-240(alpha, alpha'f) surrogate reaction

The average prompt-fission-neutron multiplicity (nu) over bar 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 (nu) over bar for Pu-239(n, f) via Pu-240(alpha, alpha'f) reactions. A Pu-240 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 (nu) over bar were obtained for a continuous range of equivalent incident neutron energies between 0.25 and 26.25 MeV, and the results agree well with direct neutron measurements.