Novel X-ray method for better screening at airports

In a bad news for smugglers and terrorists, scientists have developed a method of using X-rays that can specifically highlight hazardous materials.

The imaging technique could help detect hidden nuclear material.

"The basic idea here is to use currently available technologies - spectral X-ray detectors - to get more use out of the information that is available," said co-author Andrew Gilbert, a nuclear engineer at the University of Texas in Austin.

The detectors commonly used at airports return only block images of objects, even those that comprise multiple layers of different materials.

Such scanners only count the number of X-ray photons passing through the material, and do not register the changes in energy of the X-rays.

Hence, an X-ray of a suitcase containing plutonium, lead and iron would return an image based on an average density that would not discriminate between the three materials.

In contrast, spectral radiography relies on the detection of photons at multiple energy levels once they have travelled through a material.

The spectral radiograph produced in Gilbert's simulations would show different materials and highlight those with energy ranges specific to potentially hazardous objects.

During the research, Gilbert and his colleagues modelled a layered system of plutonium, steel and cotton, on the basis of some of the materials' chemical and physical parameters, such as density.

Then they simulated an X-ray passing through to produce a spectral radiograph of the layered materials.

Using a form of Beer's Law -- an equation that describes the interaction of an X-ray beam with an object of known composition -- they were able to both identify the materials and estimate their thickness.

The next step, the researchers say, would be to test the technique in the real world.

The findings were reported in the Journal of Applied Physics.