Introduction:

Compounds with highly electronegative groups - such as the NO2 in explosives or
the halogens in chlorofluorocarbons - have high affinities for electrons. When electrons at very low energies (less than 10 meV) hit such compounds, the electrons attach efficiently, causing the compound to form a characteristic anion or to dissociate in a unique pattern.
Electrons with very low energies are produced by firing electrons into an electrostatic "mirror ," which acts like a brake - reducing the electrons to zero or near-zero kinetic energies - and then sends them back.
 

Research studies:

• A detector based on this principle is part of a system being developed by the National Aeronautics & Space Administration's Jet Propulsion Laboratory

to help the Navy find unexploded ordnance and mines in bays and harbors.