3D, interactive X-ray to offer dramatic improvement in security scans
officer of 3DX-Ray, says KDEX offers some clear advantages. “It’s a very powerful way of getting 3D information,” he says.
Graham-Rowe notes that KDEX may help in recognizing objects, but it does not ease the task of detecting or distinguishing between materials. Yet, as Rogers points out, X-rays are routinely used for this kind of analysis. The standard technique is X-ray crystallography, which relies on the diffraction pattern produced when an X-ray beam scatters off a crystalline substance. Comparing the pattern against reference images for known materials allows a range of substances to be identified. At first sight the technique appears to have little in common with security scanners, which build up an image by measuring how X-rays are absorbed by an object. Rogers and Dicken, however, have used KDEX to do both tasks simultaneously. Because only one set of detectors is measuring absorption data at any one time, the other detectors can be used to detect diffraction patterns instead. Presenting their findings at the annual Denver X-ray Conference in Colorado last week, the team showed that they could detect aluminum and aluminum oxide and tell which was which. This is just a start, says Rogers. Because each material has a unique diffraction signature, the technique could be used by customs inspectors to detect consignments of fake pharmaceuticals. Fox says that people have long been trying to deploy X-ray diffraction in security tasks, but their efforts have been stymied by the costs involved, the slowness of the machines and by the fact that the diffraction signals are weak and hard to capture. At the Denver conference Rogers and his team presented a new way to tackle this last problem without increasing the intensity of the X-rays or resorting to the large, expensive X-ray sources commonly used in diffraction analysis. Dubbed focal construct geometry, their technique involves sending the source beam through an opaque mask with holes in a ring pattern, so generating hundreds of narrow X-ray beams. Each beam will produce a conical pattern when it scatters off the material of interest. With hundreds of these beams hitting the target, the scattered cones will intersect. Arranging the beams so that these crossover points coincide with the detectors will effectively boost the signal (Journal of Applied Crystallography, vol. 43, p. 264). Evans is hopeful that the new techniques, though still in development, are the breakthrough that the security industry has been waiting for. They require no complicated moving beams or detectors and involve doing nothing to a bag beyond putting it on a regular conveyor belt, he says. It remains to be seen whether airports will be enthusiastic. Despite the favorable TSA tests, no airport has yet adopted the 10-year-old 3DX-Ray technology. Its only use has been in situations where an exceptional level of security is required, such as checks on people entering VIP areas at the Beijing Olympics. “Security in airports is a very price-sensitive issue,” says Fox. To be successful, new technology must be available at a price that the airports are willing to pay. Evans is optimistic. Two U.S. companies have started building KDEX prototypes, which could help drive down the cost of next-generation X-ray security equipment. —Read more in Keith Rogers et al., “Focal construct geometry — a novel approach to the acquisition of diffraction data,” Journal of Applied Crystallography 43, no. 2 (April 2010): 264-8 (DOI: 10.1107/S0021889810005248) (sub. req.)
