Explosive detection

Explosive detection is a non-destructive inspection process to determine whether a container contains explosive material. Explosive detection is commonly used at airports, ports and for border control.

Detection tools

Dogs

Specially trained dogs can be used to detect explosives using their noses which are very sensitive to scents. While very effective, their usefulness becomes degraded as a dog becomes tired or bored.

These dogs are trained by specially trained handlers to identify the scents of several common explosive materials and notify their handler when they detect one of these scents. The dogs indicate a 'hit' by taking an action they are trained to provide, generally a passive response.

The explosive detection canine was originated at the Metropolitan Police Department in Washington, D.C. in 1970, by then trainer Charles R. Kirchner.

Honey bees

This approach couples trained honey bees with advanced video computer software to monitor the bee for the strategic reaction. Trained bees serve for 2 days, after which they are returned to their hive. This proven system is not yet commercially available. Biotechnology firm Inscentinel claim that bees are more effective than sniffer dogs.

Mechanical scent detection

Several types of machines have been developed to detect trace signatures for various explosive materials. The most common technology for this application, as seen in US airports, is Ion Mobility Spectrometry (IMS). 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. The time that it takes for an ion, in IMS, to move a specified distance in an electric field is indicative of that ion's size to charge ratio: ions with a larger cross section will collide with more gas at atmospheric pressure and will therefore be slower.

Gas Chromatography (GC) is often coupled to the detection methods discussed above in order to separate molecules before detection. 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. Unfortunately, GC normally requires a bottled gas, which creates a consumable and ease of use issue for the system. GC columns operated in the field are prone to degradation from atmospheric gases and oxidation, as well as bleeding of the stationary phase. Columns must be very fast, as well, since many of the applications demand that the complete analysis be completed in less than a minute.

Spectrometry

Technologies based on IMS include Ion Trap Mobility Spectrometry (ITMS, a GE technology), and Differential Mobility Spectrometry (DMS). Amplifying Fluorescent Polymers (AFP)use a molecular recognition to "turn off"/quench the fluorescence of a polymer. Chemiluminescence was used frequently in the 1990s, but is less common than the ubiquitous IMS. 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 colourless when it reacts with nitrogen groups.

One technique compares reflected ultraviolet, infrared and visible light measurements on multiple areas of the suspect material. This has an advantage over olfactory methods in that a sample does not need to be prepared. A patent exists for a portable explosive detector using this method.

X-ray machines

Specially designed X-ray machines can detect explosives by looking at the density of the items being examined. They use Computed axial tomography based systems that are enhanced with dedicated software, containing an explosives threat library and false - color coding, to assist operators with their dedicated threat resolution protocols. X-ray detection is also used to detect related components such as detonators, but this can be foiled if such devices are hidden inside other electronic equipment.

Neutron activation

Specially designed machines bombard the suspect explosives with neutrons, and read the gamma radiation decay signatures to determine the chemical composition of the sample. Explosive materials all have similar ratios of carbon, hydrogen, nitrogen and oxygen, which the machine is able to detect.

Detection aids

A detection taggant can be added when explosives are made to make detection easier. An example of this is with Semtex, which now is made with ethylene glycol dinitrate added as a detection taggant. DMDNB is a common taggant as dogs are sensitive to it.

See also

• Bloodhound
• Counter-terrorism
• Scent hound
• Terrorism

References