Science: Containing danger: James Curtis looks at some of the new hi-tech weapons in the war against smuggled drugs and explosives

LAST month's IRA attack on the City of London highlighted Britain's vulnerability to terrorist attack. It seems likely that at least some of the ammonium nitrate - which provided the explosive power for the bomb - was smuggled through a British port from a cache in Ireland.

From a terrorist's viewpoint, hiding arms or explosives in sea freight is a relatively safe bet. Most sea cargo is carried in steel containers, which come in unit sizes of 20ft, 40ft and 45ft. They are indistinguishable, apart from logos and colour, and are completely anonymous.

Unlike airports, seaports are not equipped with sophisticated screening equipment with which to analyse a container's contents. Any container or truck that is intercepted by Customs has to be manually searched - and that can take hours.

For ports such as Felixstowe, which handles more than 4,000 containers a day, widespread manual searches would cause havoc. Consequently, the proportion of containers thoroughly searched in the UK is less than 1 per cent.

Thanks to advances in X-ray technology, ports can now install systems that can screen an entire truck or container in two to three minutes. The main barrier to developing systems of this scale has been the lack of detectors able to cope with the beam of high-energy X-rays needed to penetrate an 8ft-wide container. The energy required is between 6 and 10 million electronvolts (MeV). The maximum energy of an airport baggage X-ray is 0.002 MeV.

The systems work by guiding containers by conveyor through an inspection tunnel where an image of each container's contents is transmitted to a screen.

Suppliers claim the systems will be able to inspect 20 per cent of containers going through any port. Frank Coughlin, of Analytical Systems Engineering, a US manufacturer, says: 'This may well be enough to deter smugglers.'

Research into automatic cargo inspection is well advanced in the US, where a federally funded counter-smuggling initiative has been established by the Advanced Research Projects Agency (ARPA). One of the systems being evaluated by the agency is an automated container X-ray system for use in ports and at border crossings. The Non-intrusive Examination System (NES) has been developed by a German-American consortium comprising Heimann Systems, Siemens, Analytical Systems Engineering Corp and Automated Handling Systems.

The first fully operational NES test site has been built at Tacoma, Washington, one of the busiest container ports in America. ARPA has funded the project to the tune of dollars 6.9m (pounds 4.5m).

Housed in a purpose-built inspection centre, the NES comprises a high energy X-ray integrated with information processing software and high-resolution colour displays. Containers are exposed to two X-ray beams which provide the analyst with vertical and horizontal views of the container. Imaging takes three minutes and scan analysis between five and 15 minutes, depending on the cargo.

A similar system has been developed by British Aerospace's Systems and Equipment Division (BASE). It offers a linear accelerator X-ray screening system and a trace detector - a 'sniffing' device based on a mass spectrometer that will identify traces of explosives or drugs left on the outside of a container. Samples from areas of the container likely to have been touched during loading are fed into the mass spectrometer.

John Branch of BASE says once the sample is inside the spectrometer, the 'sniffer' will identify any substance. 'The problem,' he says, 'is getting it in.'

A French detection expert says this is the chief limitation of vapour sampling: 'For it to really work, you have to get inside the container or drill a hole.' If the vapour can be obtained, a police anti-terrorist source says, 'The level of traceability now available would allow you to detect a tumbler of orange juice tipped into Windermere.'

In France, Schlumberger, the international hi-tech engineering company, has upgraded its air cargo screening system to handle sea containers of up to 48ft. This system, which is X-ray based, will be operational at the Le Havre by 1994 - the first installation in a European port.

Schlumberger has also sold two systems to Eurotunnel, operator of the Channel Tunnel. They are being installed - one at Folkestone, the other at Calais - in time for the tunnel's opening next year. According to Paul Elliot, chairman of the European arm of the American Society of Industrial Security, the tunnel is a prime terrorist target.

However, the most promising area of research lies in nuclear analysis. Drugs can be recognised by their rich carbon, chlorine and hydrogen content, and relative lack of oxygen and nitrogen. Plastic explosives are relatively rich in oxygen and nitrogen, but lacking in carbon and hydrogen. When irradiated with neutrons, all emit a 'signature' of radiation.

Nuclear analysis has been limited to small packages and airport luggage. A baggage inspection system using thermal neutron analysis has been undergoing tests at Gatwick airport. However, thermal neutrons do not have sufficient penetration to probe an entire container and produce a high false alarm rate.

In the US, Science Applications International Corporation (SAIC) has patented a nuclear technique capable of producing a three-dimensional map of a container's contents. This technique, known as pulsed fast neutron analysis (PFNA) uses nanosecond pulses of fast neutrons as the probing radiation.

Using PFNA to scan food is safe, according to a report by the UK Atomic Energy Authority and the National Radiological Protection Board (NRPB) for the Ministry of Agriculture. But a NRPB spokesman adds: 'The effect on other cargoes is a different matter.' For example, commodities such as aluminium have a high activation risk when irradiated. It is not in anybody's remit to analyse the effects of PFNA on inanimate cargo.

PFNA was to be included in the Eurotunnel contract but security sources say the technology was not sufficiently proven. Doug Brown, assistant vice-president of SAIC, says the reason was cost - between dollars 5m and dollars 10m.

Many in the industry keep faith with more traditional counter-smuggling methods. Until automated detection systems and computerised intelligence for sea cargo is improved, sniffer dogs remain one of the most effective detection tools.

It seems that pounds 1,500 on training a sniffer dog may be a wiser investment than forking out several million pounds.

The author is deputy editor, 'Port Development International'.

(Photograph omitted)