Reporter 429, 18 January 1999
University physicists have developed equipment to detect hidden explosives that could soon revolutionise air safety and anti-terrorism measures worldwide.
The pioneering apparatus is cheaper and thousands of times more powerful than anything currently available - it can detect the equivalent of a pin head of explosive material in Wembley stadium, while the current techniques would struggle to find it inside a squash court.
Developing technology sensitive enough to find explosives has proved so difficult that airports throughout the world are forced to use sniffer dogs to help screen baggage. The dogs are surprisingly effective, but are subject to fatigue and lapses of concentration.
X-ray scanners can detect large amounts of explosives but can be baffled by disguising the material - and have even confused plastic explosive with Christmas pudding.
Professor David Batchelder and Dr Simon Webster have been working on the project with the Home Office Police Scientific Development branch and the chemistry department at the University of Strathclyde.
Like its canine counterparts, the compact apparatus identifies the tell-tale traces of vapour given off by the hidden cargo - but with much greater sensitivity and reliability. The new equipment can also be used to check large freight containers that are often inaccessible to dogs and impossible to X-ray.
The equipment uses the principle that every material vibrates at a unique frequency. The distinctive vibration of different types of explosive can be picked out using beams of laser light.
The scattered light returning is usually extremely weak and the equipment's extreme sensitivity is based on being able to amplify it millions of times by mixing it with a dye and silver colloid. This allows even a single molecule of explosive to be detected under favourable conditions.
Its extreme sensitivity also gives it the potential to detect Semtex - one of the terrorists' most deadly weapons. "Semtex doesn't give off much vapour so it's very difficult to detect unless you know exactly where to look," said Professor Batchelder.
The ability to detect trace amounts of explosives means the device also has important uses in forensic science. Semtex residue, for example, is extremely difficult to remove and laboratory tests have shown the detection apparatus can still pinpoint it in fingerprints - even after repeated hand washing.
Testing in this way also reduces the chance of making crucial mistakes. "As well as being extremely reliable, the test is completely non-destructive so the evidence could be stored and re-examined whenever necessary," said Dr Webster. Field trials of the prototype machine will take place in the summer.
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