Phoenix has demonstrated direct detection of buried explosive material by interrogation with an intense neutron source in a laboratory environment. The technique analyzes neutron-induced emission of characteristic gamma rays by each element, so it senses the explosive material itself. The high yield of the Phoenix neutron generator (up to 3x10^11 neutrons/second) represents a leap in detection times and standoff distances for neutron-based IED detection technology.
Detection experiments ranged from standoff distances of up to 7 meters, which was the limit of the laboratory space. Simulants for nitrogen-based explosives were buried in sand of different moisture levels at depths of up to 28 cm (distance to top of explosive). The fast, high-resolution gamma-ray detector array is placed 50 cm above the suspect location.
The method follows a concept of operations which assumes a selection of high-risk locations have been identified using ground-penetrating radar or satellite. The location is then scanned to determine the presence of explosives. The gamma radiation emitted due to the activation is analyzed to determine a presence of 10.8 MeV nitrogen gammas higher than background. The technique can also be used as a primary detection method.
The measurements validate Monte Carlo modeling of neutron-based activation techniques. Example detection times: 1.4 seconds for 30-liter jug of TNT buried 8 cm in wet soil at a standoff of 5 m, or 37 seconds for 10-liter of TNT buried 30 cm in dry sand at a standoff of 10 m.