A Collection and Distillation of the Important Physics for Understanding, Interpreting, and Evaluating Neutron-Based Non-Destructive Assay Techniques for Nuclear Fuel

In recent years, the US Department of Energy has renewed research in a wide variety of non-destructive- assay (NDA) techniques, through its Next Generation Safeguards Initiative (NGSI). Of the fourteen technologies that are being considered in the NGSI, ten technologies measure neutrons to determine the fissile content of the nuclear material. These ten techniques can be categorized according to the characteristic of the neutrons that they measure. Five techniques measure the multiplication of neutrons by fissile material, three analyze the neutron energy spectrum for resonance reactions in fissile isotopes, and two measure the time coincidence of the neutrons that are emitted by fission. A basic knowledge of these principles is essential for understanding these techniques. This paper summarizes parts of this knowledge.