Neutrons emitted by a radioactive source cause specific nuclei to emit y -rays of characteristic energies. Thermal, or slow, neutrons activate nitrogen and chlorine, for example. Fast neutrons activate carbon and oxygen, among others. The San Diego company Science Applications International Corp. has developed and tested a prototype based on thermal neutrons. A related technique developed by researchers at Western Kentucky University, Bowling Green, and at Tennessee's Oak Ridge National Laboratory bombards a target with pulses of fast neutrons.
Identification is based on the elemental profiles indicated by the combined y -rays.
The technique has been shown to differentiate unexploded ordnance from nonexplosive materials in tests conducted for the Department of the Army to remediate proving grounds. Nuclear quadrupole resonance. Some nuclei, such as nitrogen-14, possess electric quadrupole moments. When compounds with such nuclei are probed with radio-frequency signals, they give rise to unique signals defined by the specific nucleus and its chemical environment. Developed by scientists at the Naval Research Laboratory in Washington, D.C., the technology has been licensed to San Diego-based Quantum Magnetics, which is using it to develop narcotics and explosives detectors.