Security technology: A new scanning technology, which can see things X-rays cannot, could help to beef up the inspection of air freight

AIRLINE passengers might be forgiven for thinking that security inspections are already quite tight enough, thank you. For accompanied luggage, they probably are. But accompanied luggage is only a fraction of what aircraft carry around. The rest is commercial freight, which is harder to examine with the rigour that is applied to passengers' baggage.

Part of the reason is that when an X-ray machine is faced with a containerful of cargo, the image it produces may be confused by the large number of objects packed inside. In addition, X-rays are poor at distinguishing between objects of identical shape but different composition. That is particularly true if the objects are made of material with a low density—as both explosives and drugs are. Moreover, something hidden in a container that is opaque to X-rays will not be noticed at all.

Of course, other security measures, such as explosive sniffers, can be employed, and often are. But the most reliable alternative to X-ray scanning, hand-searching everything, is slow and expensive. The upshot is that contraband is frequently smuggled in cargo and one day a bomb may be, too.

A joint venture just announced by Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) and Nuctech Company, a security-equipment maker based in Beijing, is setting out to improve the situation by combining traditional X-ray scanning with a second scan using neutrons. In combination, the two techniques should be better at spotting threats than X-rays are alone.

The new system, adapted from mineral-analysis technology, exploits differences in the amount of X-ray and neutron energy absorbed by different types of material. By combining two sources of data it is easier to understand the nature of an object than if only one is employed.

The container to be examined passes on a conveyor belt into a tunnel shielded by steel and concrete to protect operators from radiation. The X-rays come from a standard X-ray machine. The neutrons are generated by bombarding a heavy form of hydrogen, called tritium, with a lighter isotope of the gas, called deuterium. The resulting collisions create helium atoms and a stream of neutrons.

The X-ray and neutron beams pass across the tunnel through the cargo and are detected on the other side. The detectors measure how much of each type of radiation got through. A computer then compares the results with the known absorption properties of different types of materials, to work out what the objects in the container are made from. It adds this information, suitably colour-coded, to the image. The whole process takes about a minute, and the scanner can be slotted into existing airport freight-handling systems. Security personnel can thus detect suspicious objects at a glance, and either clear the container for loading or redirect it for close inspection.

In trials conducted last year at Brisbane Airport, a prototype was able to detect a range of explosives, drugs and other contraband. The system can also distinguish nuclear materials, such as uranium, from other heavy metals, according to Nick Cutmore, a CSIRO researcher who is leading the project. And it can spot non-metallic materials, such as drugs and explosives, hidden inside large metal objects that are opaque to X-rays.

The CSIRO and Nuctech plan to conduct trials on the next version of the scanner in Beijing at the end of the year. If it works there, it will be offered for general sale, and a potential loophole in airport security will thus gradually be closed.