Detection of special nuclear material and other contraband by prompt and/or delayed signatures from photofission

A method of examining contents of an object, the method comprising:

• injecting a plurality of radiofrequency power pulses into an accelerator, the plurality of radiofrequency power pulses being separated by first gaps;
• injecting a plurality of charged particle pulses into the accelerator while each of the plurality of radiofrequency pulses are injected into the accelerator, the plurality of charged particle pulses being separated by second gaps smaller than the first gaps;
• impacting a target material by each of the plurality of accelerated charged particles to generate macropulses of radiation corresponding to each radiofrequency pulse, each macropulse being separated by the first gaps and containing a plurality of micropulses of radiation corresponding to the plurality of charged particles injected into the accelerator during each radiofrequency power pulse;
• scanning an object by the plurality of consecutive macropulses of radiation comprising the respective pluralities of consecutive micropulses of radiation;
• checking for prompt gamma rays detected in respective first time periods in respective second gaps between respective consecutive micropulses of radiation and not during any of the respective consecutive micropulses, the respective first time periods being based, at least in part, on respective expected arrival times of prompt gamma rays at a first detector resulting from photofission within the object, if any, induced by a respective consecutive micropulse;
• checking for prompt neutrons detected in respective second time periods in respective second gaps between respective consecutive micropulses of radiation and not during any of the respective consecutive micropulses, the respective second time periods being based, at least in part, on respective expected arrival times of prompt neutrons at a second detector resulting from photofission within the object, if any, induced by a respective consecutive micropulse;
• checking for delayed gamma rays detected in respective third time periods in respective first gaps between respective consecutive macropulses of radiation and not during either of the respective consecutive macropulses, the respective third time periods being based, at least in part, on respective expected arrival times of delayed gamma rays at the first detector resulting from photofission within the object, if any, induced by a respective consecutive macropulse;
• checking for delayed neutrons detected in respective fourth time periods in respective first gaps between respective consecutive macropulses of radiation and not during any of the respective consecutive macropulses, the respective fourth time periods being based, at least in part, on respective expected arrival times of delayed neutrons at the second detector resulting from photofission within the object, if any, induced by the respective consecutive macropulse;
• and
• determining whether the object at least potentially contains Special Nuclear Material based, at least in part, on the checks for the detection of the prompt gamma rays, prompt neutrons, delayed gamma rays, and/or delayed neutrons.