Time-Resolved Digital Data Processing Enhancements in
Neutron Active Interrogation

Detecting shielded contraband material, including illicit drugs, explosives, and special nuclear material using nuclear techniques has been a persistent technical challenge. The signatures from contraband materials are often relatively weak and poorly separated from the background, requiring the use of long measurement times and high radiation doses from the interrogating source. We are exploring new digital pulse processing techniques for active neutron interrogation to enhance the detection of concealed contraband and special nuclear material with a focus on prompt gamma-ray signatures for drug and explosive detection and fast neutron detection for special nuclear material. The new detection systems make use of digital data acquisition from inorganic and organic scintillators along with the time structure of deuterium-deuterium and deuterium-tritium fast neutron generator interrogation sources to improve the signal-to-noise ratio of the measurements. The detection system additionally makes use of a reconfigurable water-based collimation system to reduce the production of activation gamma rays in the environment and to shield the detectors from fast and thermal internal neutron activation. We characterized the fast neutron time profile of the Thermo Scientific P211 DT neutron generator using organic scintillators and a gamma-blind He-4 recoil-based fast neutron detector. We discuss the spectral and time profiles resulting from active interrogation measurements performed with various contraband simulants and a range of inorganic scintillators, including fast inorganic scintillators such as LaBr3. We additionally discuss maximum likelihood estimation maximization-based spectral reconstruction techniques in conjunction with detecting prompt gamma rays with organic scintillators. We show the detection of prompt inelastic gamma-ray signatures from carbon- and nitrogen-rich objects that may allow for the measurement of sample stoichiometry to distinguish explosive and narcotic contraband from benign samples. Based on these methods, combined spectro-temporal analysis is being developed for detecting shielded contraband with improved sensitivity