Scientists work on IRA bomb detector: Whitehall gives top priority to 'sniffer' to identify explosives

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GOVERNMENT scientists are working secretly to develop technology capable of detecting terrorist arms and explosives concealed within vehicles, reliable security sources say.

The project, under way for more than a year, has been given the highest Whitehall priority. The hope is that technology can be used to detect Semtex explosive and the type of fertiliser the IRA hid in a tipper truck to devastate the City of London last Saturday.

The Government wants to be able to penetrate even large container lorries, which security sources believe are used frequently by the IRA to move materials within Ireland and between Ireland and Britain.

One mainstay of the IRA campaign in Northern Ireland has been its continuing ability over 20 years to move to Ulster arms and explosives from 'deep dumps' in the Irish Republic.

Hundreds if not thousands of lorries regularly move throughout Ireland and on ferries to Britain. Container lorries in particular are so large that a thorough search can take hours.

One security source said: 'The technology does not exist to drive a container lorry through an arch and come out the other side either with a clean bill of health or with a big red alarm bell ringing.'

However, experts feel such technology is within reach. Devices would have to rely on a combination of approaches. 'Sniffer' machines would depend on traces of explosive left on the vehicle's outside. Even the most up-to-date of X-ray probe technology would need time to check contents.

The best solution would be to check vehicles where traffic is moving slowly, say at ports, using a cheap, portable machine which police could set up at semi-permanent roadblocks.

One US detection expert, who wished to remain anonymous, said that given sufficient development funds industry could modify detection technology to do that - perhaps even to spot guns or explosives from the roadside as vehicles passed.

'At a cost you could make devices now that could find car bombs in critical areas, if you slowed the traffic right down. But outside Harrods, say, where you are talking about big lorries and buses and a large volume of traffic - I don't think so,' he said.

So far, time and money has been focused on systems to detect explosives at airports. These machines cost hundreds of thousands of pounds, so would be a practical solution only if used, say, at either end of Whitehall, or on key routes at times of heightened threat.

Producing a cheaper roadside version would involve meeting new criteria - moving, metal-sided targets, carrying people and cargo that radiation might harm. That limits the type of radiation that could be used. Microwaves would not penetrate metal, and neutron radiation could harm passengers.

X-rays are still the most promising probes. Combinations of high and low energy beams can help to differentiate between metallic and non- metallic objects. Comparisons of beams set at different angles indicate whether contents are organic material, dense enough to be a bomb. An automatic machine that scans baggage with two X-ray beams, each with two different energies, is on trial at San Francisco airport, and begins trials at a British airport this spring.

If the Government's research programme creates a workable machine, its best use might be to filter out only the most suspicious vehicles for traditional manual checks.

Systems are being developed to look at cargo, for example on lorries passing through the Channel tunnel. They will have only a couple of minutes to check each vehicle's contents if they are not to disrupt traffic.