Introduction:

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.
 

Research studies:

• San Diego-based 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. y-Ray emission data are collected on the pulse from nuclei reacting with fast neutrons, in between pulses from nuclei reacting with slow neutrons, and when the pulse is turned off temporarily from nuclei that undergo ß-decay, such as sodium and silicon. 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.