Lanthanum halides improve thermal neutron activation landmine detection - a comparison of fast inorganic scintillators

The Improved Landmine Detector System is a vehicle-mounted multi-sensor landmine detector, conceived and developed by Defence R&D Canada (DRDC). Suspicious targets are identified by fusing data from scanning sensors. A Thermal Neutron Activation (TNA) detector, developed by DRDC and Bubble Technology Industries (BTI), then confirms the presence of a mine by detecting the bulk nitrogen in its explosives. While the first generation TNA detector has been fielded by the Canadian Forces, DRDC and BTI have continued development and optimization of a second generation TNA sensor based around an electronic neutron generator source. By implementing faster detectors, faster electronics and more intense neutron sources, it is possible that this system could achieve 10 to 15 times higher rates, allowing correspondingly higher sensitivity or shorter detection times for landmines. The chief bottleneck to achieving the maximum possible performance from the present TNA or a future system is the relatively slow fluorescent decay time of the NaI(Tl) scintillators which are currently used. An experimental investigation was undertaken to compare a number of modern, fast inorganic scintillators to NaI(Tl) with respect to parameters relevant to TNA, including efficiency, energy resolution, linearity, available size and cost. This paper presents results in the context of the high-rate, high-gamma-energy environments expected in a TNA application. Large (7.62 cm × 7.62 cm) LaBr3:Ce scintillators, and to a lesser degree LaCl3:Ce, were found to stand-out as as the principal candidates for the detector upgrade to the TNA confirmation system. Their properties also make them ideal candidates for fast neutron activation and associated particle imaging bulk explosives detectors.