JOINT RESEARCH CENTRE

Pulsed Neutron Facility for Research in Illicit Trafficking and Nuclear Safeguards

Abstract: 
The Joint Research Centre has taken into operation a new experimental device designed for research in the fields of nuclear safeguards and illicit trafficking. The research projects currently undertaken include detection of shielded contraband materials, and mass determination of small fissile materials in shielded containers. The device, called the Pulsed Neutron Interrogation Test Assembly (PUNITA), incorporates a pulsed 14-MeV neutron generator and a large graphite mantle surrounding a sample cavity. The sealed (D, T) neutron generator emits neutrons in 10-microsecond pulses. After a slowing-down time of about 300 ┬Ás, an average thermal neutron lifetime of about one millisecond is achieved in the graphite moderator and the sample cavity. By pulsing the neutron generator with a frequency in the range of 10 to 150 Hz, a sample may be interrogated first by fast neutrons only, and a few hundred microseconds later by a pure thermal neutron flux. For the detection of materials such as explosives the device 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 device employs about one hundred 3-He 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