Ion-trap mass spectrometry. Negative ions produced by ionization of analyte molecules accumulate in an ion trap in a mass-selective fashion. Molecular ions corresponding to explosives are excited to dissociate into fragments. 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.