Patent Number: 
Section: claims

1. A system for the detection of special nuclear materials (SNM) in a first volume comprising:an associated-particle neutron generator positioned to emit neutrons toward at least a portion of the first volume;a plurality of gamma ray detectors that eachare positioned around the portion of the first volume,are capable of nanosecond timing, andproduce output data that correlates to the quantity of gamma rays received by the detector within a timing gate; anda device that acquires and processes the output data from each gamma ray detector to produce an identification output signal when the output data indicates that each of at least n adjacent detectors of the plurality of gamma ray detectors detected at least one gamma ray within their respective defined periods of time,where n>2 and the timing gates of the detectors are related. 2. The system of claim 1 wherein the plurality of gamma ray detectors are noble liquid detectors. 3. The system of claim 1 wherein the device locates fissionable material within a voxel within the first volume. 4. The system of claim 1 also comprising an alpha particle detector. 5. The system according to claim 1 wherein the plurality of gamma ray detectors collectively cover at least about fifty percent of the solid angle that the surface of the first volume subtends as observed from the cross-sectional center of the larger space. 6. The system of claim 4 wherein background noise caused by gamma rays not originating from SNM is reduced by adjusting the detector timing gate coincident with the detection of an alpha particle. 7. The system of claim 4 wherein the alpha particle detector is pixilated. 8. The system of claim 1 wherein the gamma ray detector is pixilated. 9. The system of claim 1 wherein gamma ray detection signals are collected in a time gate of 20 nanoseconds or less. 10. A method of interrogating a sample volume for the detection of fissionable materials comprising:a. impacting a sample with neutrons from an associated-particle neutron generator;b. detecting gamma rays emitted from fissionable material impacted by ballistic neutrons generated by the neutron generator by means of a number n of detectors during a timing gate, where n is three or more and the timing gates for the respective detectors are related; andc. outputting to a user interface a signal indicating the coincident detection of gamma rays by each of at least n adjacent detectors. 11. The method of claim 10 wherein the detectors are positioned around the sample. 12. The method of claim 10 wherein the starting point of the timing gate is adjusted as a function of the timing of the detection of an alpha particle. 13. The method of claim 10 wherein the number n is at least four. 14. The method of claim 12 wherein a pixilated alpha particle detector provides angular separation and on the order of nanosecond timing of the detection of gamma rays and yields depth of field to establish the location of SNM in a sample volume, and outputting to a user interface the detection of gamma rays and the location of SNM within a sample volume. 15. The method of claim 13 wherein the detectors each have pixels that detect the gamma rays, the method further comprising calculating the location of the intersection of arcs extended from the pixels actually detecting the gamma rays, outputting to a user interface the detection of gamma rays and the location of SNM within a sample volume. 16. The method of claim 10, wherein the detectors are noble liquid detectors.