Pulsed Neutron Facility for Research in Illicit Trafficking and Nuclear Safeguards

The Joint Research Centre has taken into operation a new experimental facility designed for research in the fields of illicit trafficking and nuclear safeguards. The research projects currently undertaken include detection of shielded contraband materials (drugs, explosives, nuclear materials), and mass determination of small fissile materials in shielded containers. The facility, called the Pulsed Neutron Interrogation Test Assembly (PUNITA), incorporates a pulsed 14-MeV D-T neutron generator and a large graphite mantle surrounding a sample cavity. The sealed generator emits neutrons in 10-microsecond pulses. After a slowing-down time of approximately 300 mus, an average thermal neutron lifetime of approximately one millisecond is achieved in the graphite moderator and the sample cavity. By pulsing the neutron generator with a frequency between 10 to 150 Hz, a sample may be interrogated first by fast neutrons, and a few hundred microseconds later by a pure thermal neutron flux. For the detection of materials such as explosives the facility employs gamma detectors for characteristic prompt gamma rays from inelastic scattering by fast neutrons, and from thermal neutron capture. The gamma detectors include HPGe detectors and lanthanum bromide scintillation detectors. This new type of scintillation detector is particularly suited for the detection of activation gamma rays in the MeV range. For the purpose of fissile material assay (nuclear safeguards) the PUNITA facility employs 96 ³He proportional counters located on the outside of the graphite liner and embedded in cadmium covered polyethylene modules. The paper reports about the design and characterization of the new research facility as well as the different experimental configurations employed for the research activities in the fields of illicit trafficking and nuclear safeguards.