The gas-filled X-ray tube
Later investigation showed that X-rays were produced whenever fast moving electrons were stopped on impact with a target. This led to the development of tubes containing air at very low pressure in which a beam of cathode rays was focused from a concave cathode on to a tungsten disc called the anticathode (Fig. 44.7). The anticathode is set into a block at the end of a copper tube which serves the purpose of conducting away as heat, the internal energy transferred by the impact of the electrons.