Carbon nanotubes drive X-ray scanner.

A tiny technology for producing X rays in a novel way could increase the sensitivity of luggage screening at airports, medical imaging, and other techniques for looking through things and make their use more widespread.

In conventional X-ray machines, a metallic filament heated to 1,000[degrees] C emits electrons that barrel down a vacuum tube and collide with a piece of metal to produce the rays. The new X-ray device, designed by Otto Zhou of the University of North Carolina at Chapel Hill and his colleagues, relies instead on a film of carbon nanotubes that emits electrons at room temperature when exposed to an electric field. It's a much less energy-consuming process, Zhou says.

Inside the new device, each of five carbon-nanotube films yields an image of an object from a separate angle. Computer software compiles the images to produce a three-dimensional picture.

The nanotube-based scheme, described in the May 2 Applied Physics Letters, could lead to cheaper, smaller, and faster X-ray scanners, says Zhou. Existing security scanners at airports generate 3-D images using a single X-ray source that slowly rotates around a piece of luggage, gathering images from different projections. The machines are bulky and the image processing is slow. Zhou contends that a device containing as many as 100 carbon-nanotube electron emitters would have no moving parts and yet could produce a sharper 3-D image.

He and his colleagues plan to build a prototype nanotube X-ray scanner for airport-security screening by the end of this year. Xintek, a company cofounded in 2000 by Zhou and based in Research Triangle Park, N.C., is commercializing the technology.