Abstract: Radiation from special nuclear materials (“SNM”) is analyzed by detecting and sampling gamma rays and fast neutrons. If the amplitude of a recorded gamma ray induced signal or neutron induced signal exceeds a predetermined threshold, signal arrival times, and characteristic pulse shape parameters and/or full integrals of the sampled signals are measured. Based on the signal arrival times, and the characteristic pulse shape parameters and/or the full integrals of the sampled signals, it is determined if a neutron induced signal is recorded within a predetermined time window after a recorded gamma ray induced signal. If so, possible points of origin of the correlated neutron and gamma rays within a field of view are reconstructed. If a rate of events with a neutron-induced signal being recorded within the predetermined time window after a recorded gamma ray signal is higher than a predetermined value above the background rate. An alarm is issued.

Abstract: Radiation from special nuclear materials (“SNM”) is analyzed by detecting and sampling gamma rays and fast neutrons. If the amplitude of a recorded gamma ray induced signal or neutron induced signal exceeds a predetermined threshold, signal arrival times, and characteristic pulse shape parameters and/or full integrals of the sampled signals are measured. Based on the signal arrival times, and the characteristic pulse shape parameters and/or the full integrals of the sampled signals, it is determined if a neutron induced signal is recorded within a predetermined time window after a recorded gamma ray induced signal. If so, possible points of origin of the correlated neutron and gamma rays within a field of view are reconstructed. If a rate of events with a neutron-induced signal being recorded within the predetermined time window after a recorded gamma ray signal is higher than a predetermined value above the background rate. An alarm is issued.