X-RAY TUBE

also called Roentgen Tube, vacuum tube that produces X rays by accelerating electrons to a high velocity with a high-voltage field and causing them to collide with a target, the anode. Because X rays can penetrate solid substances to varying degrees, they are applied in medicine and dentistry, in the exploration of the structure of crystalline materials, and in research. The tube consists of a source of electrons, the cathode, which is usually a heated filament, and an anode, usually of tungsten, which is enclosed in an evacuated glass envelope. The X-ray tube functions on the principle that X rays are produced wherever electrons moving at very high speeds strike matter of any kind. The X-ray tube design that became the prototype for subsequent devices was invented by the American engineer William D. Coolidge in 1913.