Jo Crossett, age 12, of Kansas City, Kan., for her question:
WHO DISCOVERED X RAYS?
X rays were discovered in 1895 by a German physicist named Wilhelm Roentgen. He called them X rays because at first he did not understand what they were. "X" is a scientific symbol for the unknown.
Now we know that X rays are one of the most useful forms of energy. X rays are a kind of electromagnetic radiation, which also includes visible light, radio waves and gamma rays.
Visible light and X rays have many characteristics in common. Both travel at the speed of light: 186,282 miles per second. Both X rays and light travel in straight lines in the form of related electric and magnetic energy called electromagnetic waves. Also, X rays darken photographic film in much the same way that light does.
Light and X rays differ in terms of wavelength, or the distance between two crests of an electromagnetic wave. The wavelengths of X rays are much shorter than those of light.
Because of their short wavelengths, X rays can penetrate deeply into many substances that do not transmit light. The penetrating power and other characteristics of X rays make them extremely useful in medicine, industry and scientific research.
X rays can actually cause physical, chemical and biological changes in substances. If the rays are absorbed by a plant or animal, they may damage or even destroy living tissue. For this reason, X rays can be dangerous. Dentists and radiologists take special care not to overexpose their patients or themselves to the rays.
In nature, X rays are produced by the sun, other stars, pulsars and certain other heavenly bodies. Most X rays from sources in space are absorbed by the atomosphere before they reach the earth.
Man made X rays are produced chiefly with X ray tubes, a principal part of X ray machines. Devices that accelerate atomic particles also produce X rays.
In medicine, X rays are widely used to make X ray pictures, or radiographs, of the bones and internal organs of the body.
A radiograph is made by passing a beam of X rays through a patient's body onto a piece of photographic film. The bones absorb more of the rays than do muscles or other organs, and so the bones cast the sharpest shadows on the film.
Others parts of the body allow more X rays through than the bones do and cast shadows of varying density. The shadows of the bones show up clearly as light areas on a radiograph, and the organs are seen as darker areas.
Radiologists can see a patient's organs actually functioning by means of an X ray device called a fluoroscope. The rays cause a special screen in the fluoroscope to fluoresce or glow when they strike it.
X rays are also widely used to treat cancer. They kill cancer cells more readily than they kill normal cells. A cancerous tumor can be exposed to a limited dose of X rays. In many cases, the X rays destroy the tumor but do less damage to nearby healthy tissue.