Scots scientist invents test to detect Semtex

The explosive, which was used to down PanAm Flight 103 above Lockerbie, is notoriously difficult to detect because it gives off almost no odour.

Even sniffer dogs, whose sense of smell is many times more sensitive than humans’, are likely to be defeated by the Czech-made explosive.

But work by Dr Duncan Graham at the University of Strathclyde offers hope that hand-held detectors capable of recognising Semtex vapour will be available in the future.

Graham and his colleagues have spent seven years on the Home Office-backed research, culminating in a test which can detect a single molecule from the explosive.

Semtex is popular with terrorists because - as well as being difficult to detect - it packs a huge punch for its weight, is stable, and can be easily moulded to fit almost any shape.

In 1988, just 11 ounce were enough to blow a hole in the fuselage of Flight 103 and cause the aircraft’s disintegration, killing 270 people.

Sniffer dogs are the best line of defence, but at 50,000 each to train, are in short supply. They are also prone to being diverted from Semtex by stronger smells.

Other mechanical devices are simply too insensitive to detect the small quantities generally used by terrorists.

Graham said last night: "Obviously this has tremendous implications. In the fight against terrorism, the detection of hidden high explosives by discovering their vapour in the air is an important tool.

"I believe a hand held sampler is possible in the future. Automated mechanical sniffers could be fitted with this detection system on every baggage handling chute."

Graham’s research has just been published by The Royal Society of Chemistry. His breakthrough technique starts with a system called SERRS - advanced vibrational spectroscopy - which can be highly sensitive, cheap and easy to use.

It involves examining laser light bouncing off molecules attached to a gold surface. Each molecule has its own distinctive ‘fingerprint’.

However, RDX is hard to detect even using SERRS so the next step for Graham and his team was "making the invisible man visible".

To convert RDX into a chemical SERRS could pick up, Graham’s team eventually hit on the technique of treating it with an amalgam of sodium in mercury.

This transformed it into the compound hydrazine, which turned bright orange increasing the detection level by 1,000,000,000,000-fold.

The development means that a Semtex sensor could be fitted containing a sodium amalgam to convert RDX to a detectable substance on the spot.

First experiments suggest that such a device could sense just a few trillionths of a gram of RDX.

Yesterday a spokeswoman for the Home Office said: "This is of great importance. Using this new laser technology, explosive molecules can be detected directly from the air without any contact with the person, bag, vehicle or container being screened.

Explosive History

BEFORE Lockerbie, Semtex was little known outside of the military and demolition industries.

Semtex was invented in 1966 by Stanislav Brebera, a chemist with the Czechoslovak state firm Explosia’s parent company, Synthesia. Its name is derived from a combination of Semtn and Explosia.

Like C-4, its American cousin, Semtex - "the magic marble of Pardubice" - was malleable and putty-like and could be transported, handled and custom-fit for just about any job. Between 1975 and 1981, the Czechoslovak state export company, Omnipol, shipped an estimated 690 tons of it to Libya.

Today, Semtex is sold in two forms: the red bricks of Semtex 1A, used mostly for blasting operations, and the white sheets of Semtex 10SE, used primarily for hardening metals.