Prompt Pulsed Neutron Activation Analysis for Detection of Fission Neutrons

A pulsed-neutron interrogation technique for detection of Special Nuclear Material (SNM) is described. The technique combines timing techniques from pulsed prompt gamma neutron activation analysis with silicon carbide (SiC) semiconductor fast neutron detector technology. SiC detectors can operate during and within nanoseconds of the end of an intense neutron pulse, providing the ability to detect the prompt neutron emissions from fission events produced by the neutrons from SNM on a much faster pulsing time scale than has been achieved by other techniques. Neutron-induced fission neutrons in ²³⁵U have been observed in the time intervals between pulses of 14-MeV neutrons from a deuterium-tritium electronic neutron generator. Neutron pulsing and time-sequenced neutron counts were carried out on a hundreds of microseconds time scale, enabling the observation of prompt fission neutrons induced by the die-away of thermal neutrons following the 14-MeV pulse. SNM was detected in a variety of shielded configurations, and excellent signal-to-background ratios were observed.