Explosive detection

Colorimetric detection of explosives involves applying a chemical reagent to an unknown material or sample and observing a color reaction.

As a result, traditional colorimetric tests have a disadvantage: some explosive compounds (such as acetone peroxide) do not contain nitrogen and are therefore harder to detect.

[3] Recent studies suggest that mass spectrometric vapor analysis techniques, such as secondary electrospray ionization (SESI-MS), could support canine training for explosive detection.

This method is similar to mass spectrometry (MS), where molecules are ionized and then moved in an electric field in a vacuum, except that IMS operates at atmospheric pressure.

This not only improves the performance of the detector but also adds another dimension of data, as the time it takes for a molecule to pass through the GC may be used as an indicator of its identity.

Several attempts are being made to miniaturize, ruggedize and make MS affordable for field applications; such as an aerosol polymer that fluoresces blue under UV but is colorless when it reacts with nitrogen groups.

[6] One technique compares reflected ultraviolet, infrared and visible light measurements on multiple areas of the suspect material.

[8] Specially designed X-ray machines using computed axial tomography can detect explosives by looking at the density of the items..

[11] Specially designed machines bombard the suspect explosives with neutrons and read the resulting gamma radiation decay signatures to determine the chemical composition of the sample.

Unfortunately, the much smaller thermal Neutron cross sections of carbon and oxygen limit the ability of this technique to identify their abundances in the unknown species, and it is partly for this reason that terror organizations have favored nitrogen absent explosives such as TATP in the construction of IEDs.

Modifications to the experimental protocol can allow for easier identification of carbon and oxygen-based species, (e.g. the use of inelastic scattering from fast neutrons to produce detectable gamma rays, as opposed to simple absorption occurring with the thermal neutrons), but these modifications require equipment that is prohibitively more complex and expensive, preventing their widespread implementation.

[12] Silicon nanowire configured as field effect transistors have been demonstrated to detect explosives including TNT, PETN and RDX in sensitives superior to those of canines.

[18] …There is a rather large community of people around the world that believes in dowsing: the ancient practice of using forked sticks, swinging rods, and pendulums to look for underground water and other materials.