Multiple fast neutron and gamma-ray beam systems for the detection of illicit materials

Neutron and photon sources have been combined in order to assess the performance of these combinations to discriminate between materials of similar composition. The evaluation has been carried out on the basis of the maximum and minimum ratio values of the relative transmissions of high-energy gamma- or X-ray and neutrons. The number of materials with similar ratio values was used as an indicator of the effectiveness of each source combination. The use of three sources, instead of two, significantly improves the capability of neutron/photon combination to separate similar in composition materials.