Nanotube diagnostic x rays

The design of the x-ray tubes used in many medical and dental offices is essentially unchanged from a hundred years ago. A metal filament, the cathode, emits electrons when heated to more than 1000°C. The electrons are accelerated across a vacuum tube into a target, where they generate x rays. Now, a team of physicists and doctors at the University of North Carolina at Chapel Hill and the nearby firm of Applied Nanotechnologies Inc has created an x-ray tube using a room-temperature array of carbon nanotubes in a field-emission triode. They demonstrated a sufficiently large and stable current for practical medical imaging, as shown here by the x ray of a fish. According to the researchers, the device can be much smaller, is expected to last longer, and can produce a more focused x-ray beam than the hot-cathode design. In addition, the response time is sharper and the pulse shape and timing can be programmed, all of which help in the tracking of moving objects. (G. Z. Yue et al., Appl. Phys. Lett. 81, 355, 2002 http://dx.doi.org/10.1063/1.1492305 .)