Neutron and Gamma Ray Imaging for Nuclear Materials Identification

This paper describes tomographic imaging capabilities for fissile object identification. The tomographic capabilities add object spatial and material properties information that result in a more detailed item signature (template) and provide more information for physical attributes analyses. One method of examining fissile objects in sealed containers is through a radiation signature acquired by shining a 252Cf or DT generator source through the container and measuring the resulting radiation at detectors on the other side. This measurement gives a gamma and/or neutron radiation transmission profile of the object, mixed with the radiation produced by the induced fissions in any fissile materials. Whereas the method above measures the fissile object at a single position, tomography images the interior of an item by making transmission measurements from all angles around the object. The advantage is more geometric and materials property information. The tomographic image provides more information about the geometry of the object, which should lead to better interpretation of the radiation signature. Interrogating with both gamma rays and neutrons of varying energies allows the system to construct separate tomographic views of the object’s approximate gamma and neutron interaction properties (cross sections). The combination of geometric and materials property information will result in better template matching and attributes analysis. The paper presents Monte Carlo simulations illustrating this technique.