- Explosive detection
Explosive detection is a non-destructive
inspectionprocess to determine whether a container contains explosivematerial. Explosive detection is commonly used at airports, ports and for border control.
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. [(Newlon, Clark (1974). "Police Dogs in Action." New York, Dodd, Mead and company)]
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 Inscentinelclaim that bees are more effective than sniffer dogs. [cite web|url=http://newsvote.bbc.co.uk/mpapps/pagetools/print/news.bbc.co.uk/1/hi/technology/6972526.stm|title=Hot picks: UK tech start-ups|date=2007/09/05|publisher=BBC.co.uk]
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.
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. [cite web|url=http://technology.newscientist.com/channel/tech/dn14048-glowing-spray-lets-csi-operatives-dust-for-explosives.html
title=Glowing spray lets CSI operatives 'dust' for explosives|author=Colin Barras|date=03 June 2008
publisher=NewScientist.com news service]
One technique compares reflected
ultraviolet, infraredand visible lightmeasurements 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. [cite web|url=http://www.newscientist.com/blog/invention/2008/05/portable-explosives-detector.html|title= Portable explosives detector|date=Wednesday, May 28, 2008|author=Justin Mullins|publisher=NewScientist Blogs]
X-ray machines can detect explosives by looking at the density of the items being examined. They use Computed axial tomographybased 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.Fact|date=July 2008 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. [cite web|url=http://technology.newscientist.com/channel/tech/weapons/dn9715|title=Analysis: Explosive detection technologies|author=Will Knight|date=10 August 2006|publisher=NewScientist.com news service]
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.Fact|date=July 2008
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 dinitrateadded as a detection taggant.Fact|date=July 2008 DMDNBis a common taggant as dogs are sensitive to it.
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