ANTICATHODE, the target inserted in an X-ray tube on which the high-speed electrons, or cathode rays (q.v.), are directed. In tubes with a separate anode the anticathode is generally connected electrically, and outside the tube, to the anode (q.v.). In a Coolidge tube the anticathode acts also as the anode. On the impact of a sufficiently swift electron (q.v.) , it gives forth an X-radiation characteristic of the material of which it is composed. (See RONTGEN RAYS: Applications; and ATOMIC NUMBER.)