A high-energy prompt neutron signature for the detection of fissionable materials

In recent years, much research at the Idaho Accelerator Center has been focused on the detection of fissionable materials using a bremsstrahlung photon investigation method. A large portion of this research has focused on a fission signature derived from the emission of delayed neutrons from photofission. While this signature has proven successful, this dissertation introduces an alternative signature that utilizes the more prolific prompt fission neutron emissions. This signature monitors for prompt neutron emissions with energies not allowed by nonfission photoinduced reactions. A high-resolution neutron time-of-flight spectrometer was developed to measure this high-energy prompt signature and perform the energy discriminations required. Measurements were made to compare the sensitivities of the delayed and high-energy prompt neutron signatures at several investigating beam energies and under the effects of different types of target shielding. It was found that the high-energy prompt neutron signature outperforms the delayed neutron signature at beam energies below 12 MeV and under most shielding conditions.