Abstract: Disclosed are systems and methods for detecting fissile material. The systems and methods include devices and operations for measuring background neutron detection events using a plurality of fast neutron detectors arranged around a stimulation neutron source, measuring sample neutron detection events using the plurality of fast neutron detectors arranged around a small volume of sample material, measuring stimulated neutron detection events using the plurality of fast neutron detectors when the sample material is irradiated by the stimulation neutron source, (which in various implementations, includes determining a number of single neutron detection events), and determining a presence of fissile material in the sample material based upon the background neutron detection events, sample neutron detection events and the stimulated neutron detection events.