x-ray, 1. electromagnetic radiation with wavelengths between about 0.005 and 10 nm. X-rays are produced when electrons traveling at high speed strike certain materials, particularly heavy metals such as tungsten. They can penetrate most substances and are used to investigate the integrity of certain structures, to therapeutically destroy diseased tissue, and to make radiographic images for diagnostic purposes, as in radiography and fluoroscopy. Discrete x-rays are those with precisely fixed energies that are characteristic of differences between electron binding energies of a particular element. Tungsten, for example, has 15 different effective energies and no more, representing emissions from 5 different electron shells. Also called roentgen ray, x radiation. 2. an image made by projecting x-rays through organs or structures of the body onto an image receptor. Structures that are relatively radiopaque (allow few x-rays to pass through), such as bones and cavities filled with a radiopaque contrast medium, cast a shadow on the image receptor. 3. to make a radiograph. See also contrast medium, electron, fluoroscopy, radiopaque.
