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...