Point Kinetics Framework for Characterizing Prompt Neutron and Photon Signatures From Tagged Neutron Interrogation

The goal of this paper is to build a simple point kinetics model to predict the neutron and photon multiplicities induced by an associated particle imaging deuterium-tritium neutron generator interrogating uranium metal. A point kinetics framework is used to model the relationship between multiplication and radiation released from a 14.1-MeV neutron-induced fission chain in subcritical uranium. The goal of developing this point kinetics model is to tie the number of neutrons and photons released from a configuration to the multiplication of that configuration. The discussion is limited to building a model that describes the photon and neutron multiplicities released from a uranium inspection object, not considering the detection process. The addition of polyethylene shielding is also investigated. The point kinetics predictions are compared with the results from an MCNP-PoliMi simulation throughout as a way of measuring how closely the simple point kinetics model describes the complex propagation and transport of fission chain radiation in fissile material. The results show that the point kinetics does an excellent job of predicting the multiplicities released from the inspection objects, but at the cost of multiple additional inputs, some of which rely on the knowledge of geometric information from imaging.