ABSTRACT
X rays were discovered in 1895 by Wilhelm Roentgen, who was working with a Crookes tube (today called a discharge tube), a glass tube containing two electrodes. Kept at very low gas pressure, it can produce cathode rays and other discharges. Roentgen noticed that a nearby fluorescent screen glowed when cathode rays struck it, and that the same effect occurred even when the tube was encased in a cardboard box. X rays were first thought to be completely different from light, but in 1911 Max von Laue established that they, like light, were electromagnetic waves. X rays were put to work almost immediately when
Roentgen noted that they could penetrate matter, including the human body, and produce an image; physicians were soon doing x-ray studies of their patients. (See MEDICAL DIAGNOSTICS.)
X rays are generated whenever high-speed electrons going through an evacuated tube strike a
I target, such as a metal plate. The energy lost by the electrons in the collision is then emitted in the form of short wavelength electromagnetic radiation. Early x-ray tubes consisted of a flat or concave cathode that emitted electrons and
I a metal anode that emitted x rays. The modern x-ray tube, invented
by W. D . Coolidge, uses a hot wire to emit electrons and a massive tungsten or molybdenum anode; the tube can reach an electric potential of a million volts or more. X rays today have a wide range of uses, from medical diagnosis and treatment to the study of materials and the universe.
