Patent Number: 
Section: claims

1. A system for detecting fissionable material, the system comprising:a source configured to accelerate a pulsed beam of charged particles;a first target configured to generate a first neutron beam in response to being struck by accelerated charged particles, the first neutron beam including neutrons having a first energy that is sufficient to cause fission in a first class of fissionable material, wherein said first class of fissionable material is non-weaponizable fissionable material;a second target configured to generate a second neutron beam in response to being struck by accelerated charged particles, the second neutron beam including essentially only neutrons having a second energy that is lower than the first energy, the second energy sufficient to cause fission in a second class of fissionable material, wherein said second class of fissionable material is weaponizable fissionable material, and insufficient to cause fission in the first class of fissionable material;a sensor configured to detect radiation from a fission product; anda processor coupled to a non-transitory computer-readable storage medium, the medium storing instructions that, when executed, cause the processor to:cause the source to accelerate a first pulsed beam of charged particles toward the first target such that the first neutron beam is directed toward a physical region,cause the source to accelerate a second pulsed beam of charged particles toward the second target such that the second neutron beam is directed toward the physical region,determine, based on data from the sensor, whether the physical region includes a fissionable material, andin response to a determination that the physical region includes a fissionable material determine whether the fissionable material is part of the first class of fissionable material or the second class of fissionable material based on the data from the sensor. 2. The system of claim 1, wherein the instructions further cause the processor to receive a region of interest that is located within the physical region. 3. The system of claim 1,wherein the second pulsed beam of charged particles has the same energy as the particles in the first pulsed beam of charged particles. 4. The system of claim 1, further comprising a steering module configured to steer an accelerated pulsed beam of charged particles relative to the first target and the second target. 5. The system of claim 4, wherein the steering module is a magnet configured to control a direction of the first pulse. 6. The system of claim 4, wherein the first target and the second target are spatially separated from each other, and the steering module steers the first pulse of charged particles to the first target to generate the first neutron beam and the second pulse of charged particles to the second target to generate the second neutron beam. 7. The system of claim 1, wherein the first target and the second target are located along a target ladder that is a single piece. 8. The system of claim 1, wherein the first target and the second target are the same material. 9. The system of claim 1, wherein the first target is beryllium or deuterium, and the second target is carbon. 10. The system of claim 1, further comprising a track along which the source moves relative to a region that includes the physical region. 11. The system of claim 1, wherein the system is configured such that the data of the sensor is analyzed for the presence of delayed fission products. 12. The system of claim 11, wherein the sensor is activated only when the physical region is not irradiated by the first neutron beam or the second neutron beam. 13. The system of claim 1, further comprising an imaging sensor placed in the path of one or more of the first neutron beam and the second neutron beam. 14. The system of claim 1, wherein the source is a single energy accelerator. 15. The system of claim 1, wherein the first neutron beam is a fast neutron beam that includes neutrons having an energy greater than a threshold energy, and the second neutron beam is a slow neutron beam having neutrons having an energy less than the threshold energy. 16. The system of claim 15, wherein the instructions further include instructions to cause the processor to generate an image based on attenuation of the fast neutron beam by the physical region. 17. The system of claim 16, wherein the instructions further include instructions to analyze the generated image to identify regions that are not penetrated by the fast neutron beam. 18. The system of claim 15, wherein the processor is further configured to:receive data from the sensor indicating detection of fission radiation resulting from the slow neutron interacting with the physical region, anddetermine that the region of interest includes a weaponizable material based on the data. 19. The system of claim 15, wherein at least one neutron included in the fast neutron beam has an energy greater than 1.5 MeV, and the slow neutron beam has neutrons having an energy of less than 1.5 MeV. 20. The system of claim 15, wherein the slow neutron beam only has neutrons having an energy less than the threshold energy. 21. The system of claim 15, wherein the weaponizable material comprises a special nuclear material, and the second class of fissionable material comprises uranium-238. 22. The system of claim 15, wherein the threshold energy is about 1.2 MeV. 23. The system of claim 15, wherein the fast neutron beam further includes neutrons below 0.5 MeV.