"We believe we have made a major breakthrough in X-ray technology and we are extremely excited about it," said Otto Zhou, associate professsor of physics and materials sciences at the University of North Carolina at Chapel Hill. "If this works as well as we think it will, we can make such machines a lot smaller and cooler and will be able to turn them on and off much faster. They should also be cheaper, safer in terms of the lower heat generated, last longer, use less electricity and produce higher-resolution images."

X-ray systems generate X-rays by bombarding a metal target with high-energy electrons. Conventional devices use a metal filament heated to around 1000°C to produce the electrons, in a process known as thermionic emission: the scientists say that the basic technology has remained essentially the same for a century. In this study, on the other hand, the researchers used field emission from single-walled carbon nanotubes to pump out electrons at room temperature.

The resulting device was able to produce both continuous and pulsed X-rays with a programmable wave form and repetition rate, as well as an X-ray flux comparable to that from conventional fixed-target X-ray tubes. A carbon nanotube cathode with an area of 0.2 sq. cm gave a total emission current of 28 mA.

"We have already taken pictures of human hands and fish that are as good as standard X-rays," added Zhou. "We think our images will eventually be clearer than conventional ones since we have a more pointed, tunable source of electrons."

The scientists hope to have carbon-nanotube X-ray devices on the market within "a year or two" and say that the technology could lead to portable X-ray sources for industrial and medical applications. They reported their work in the 8 July issue of Applied Physics Letters.