<P> 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 . </P> <P> Specially designed machines bombard the suspect explosives with neutrons, and read the gamma radiation decay signatures to determine the chemical composition of sample . The earliest developed forms of Neutron Activation Analysis use low energy neutrons to determine the ratios of nitrogen, chlorine, and hydrogen in the chemical species in question, and are an effective means of identifying most conventional explosives . 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 this reason in part that worldwide 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 . </P> <P> Silicon nanowire configured as field effect transistors have been demonstrated to detect explosives including TNT, PETN and RDX in sensitives superior to these of canines . The detection in this method is performed by passing a liquid or vapor containing the target explosive over the surface of a chip containing tens to hundreds of silicon nanowire sensing elements . Molecules of the explosive material interact with the surface of the nanowires and as a result induce a measurable change in the electrical properties of the nanowire . </P> <P> A detection taggant can be added when explosives are made to make detection easier . The Montreal Convention 1991 is an international agreement requiring manufacturers of explosives to do this . An example is with Semtex, which now is made with DMDNB added as a detection taggant . DMDNB is a common taggant as dogs are sensitive to it . In the UK the relevant legislation is the Marking of Plastic Explosives for Detection Regulations 1996 . </P>

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