X ray

(redirected from roentgen ray)
Also found in: Dictionary, Thesaurus, Medical, Wikipedia.

X ray

X ray, invisible, highly penetrating electromagnetic radiation of much shorter wavelength (higher frequency) than visible light. The wavelength range for X rays is from about 10−8 m to about 10−11 m, or from less than a billionth of an inch to less than a trillionth of an inch; the corresponding frequency range is from about 3 × 1016 Hz to about 3 × 1019 Hz (1 Hz = 1 cps).

Production of X Rays

An important source of X rays is synchrotron radiation. X rays are also produced in a highly evacuated glass bulb, called an X-ray tube, that contains essentially two electrodes—an anode made of platinum, tungsten, or another heavy metal of high melting point, and a cathode. When a high voltage is applied between the electrodes, streams of electrons (cathode rays) are accelerated from the cathode to the anode and produce X rays as they strike the anode.

Two different processes give rise to radiation of X-ray frequency. In one process radiation is emitted by the high-speed electrons themselves as they are slowed or even stopped in passing near the positively charged nuclei of the anode material. This radiation is often called brehmsstrahlung [Ger.,=braking radiation]. In a second process radiation is emitted by the electrons of the anode atoms when incoming electrons from the cathode knock electrons near the nuclei out of orbit and they are replaced by other electrons from outer orbits. The spectrum of frequencies given off with any particular anode material thus consists of a continuous range of frequencies emitted in the first process, and superimposed on it a number of sharp peaks of intensity corresponding to discrete frequencies at which X rays are emitted in the second process. The sharp peaks constitute the X-ray line spectrum for the anode material and will differ for different materials.

Applications of X Rays

Most applications of X rays are based on their ability to pass through matter. This ability varies with different substances; e.g., wood and flesh are easily penetrated, but denser substances such as lead and bone are more opaque. The penetrating power of X rays also depends on their energy. The more penetrating X rays, known as hard X rays, are of higher frequency and are thus more energetic, while the less penetrating X rays, called soft X rays, have lower energies. X rays that have passed through a body provide a visual image of its interior structure when they strike a photographic plate or a fluorescent screen; the darkness of the shadows produced on the plate or screen depends on the relative opacity of different parts of the body.

Photographs made with X rays are known as radiographs or skiagraphs. Radiography has applications in both medicine and industry, where it is valuable for diagnosis and nondestructive testing of products for defects. Fluoroscopy is based on the same techniques, with the photographic plate replaced by a fluorescent screen (see fluorescence; fluoroscope); its advantages over radiography in time and cost are balanced by some loss in sharpness of the image. X rays are also used with computers in CAT (computerized axial tomography) scans to produce cross-sectional images of the inside of the body.

Another use of radiography is in the examination and analysis of paintings, where studies can reveal such details as the age of a painting and underlying brushstroke techniques that help to identify or verify the artist. X rays are used in several techniques that can provide enlarged images of the structure of opaque objects. These techniques, collectively referred to as X-ray microscopy or microradiography, can also be used in the quantitative analysis of many materials. One of the dangers in the use of X rays is that they can destroy living tissue and can cause severe skin burns on human flesh exposed for too long a time. This destructive power is used in X-ray therapy to destroy diseased cells.

Discovery and Early Scientific Use

X rays were discovered in 1895 by W. C. Roentgen, who called them X rays because their nature was at first unknown; they are sometimes also called Roentgen, or Röntgen, rays. X-ray line spectra were used by H. G. J. Moseley in his important work on atomic numbers (1913) and also provided further confirmation of the quantum theory of atomic structure. Also important historically is the discovery of X-ray diffraction by Max von Laue (1912) and its subsequent application by W. H. and W. L. Bragg to the study of crystal structure.


See D. Graham and T. Eddie, X-ray Techniques in Art Galleries and Museums (1985); B. H. Kevles, Naked to the Bone: Medical Imaging in the Twentieth Century (1997).

The Columbia Electronic Encyclopedia™ Copyright © 2022, Columbia University Press. Licensed from Columbia University Press. All rights reserved.
References in periodicals archive ?
Professor Oliver Lodge used Roentgen rays to image the wrist and the bullet was clearly identified at the base of the 3rd metacarpal.
American Roentgen Ray Society AJR 2000; 174: 1793-4.
The results were presented May 7 at the American Roentgen Ray Society annual meeting.
MIAMI BEACH -- Magnetic resonance imaging visualizes uterine fibroids in enough detail that a potentially ineffective uterine fibroid embolization can be avoided in up to 20% of patients referred for the procedure, according to a study presented at the annual meeting of the American Roentgen Ray Society.
Parker said at the annual meeting of the American Roentgen Ray Society.
Birchard said at the annual meeting of the American Roentgen Ray Society.
Michael Temple said at the annual meeting of the Roentgen Ray Society.
Leading article: InPractice; Quarterly Publication of the American Roentgen Ray Society.
By 1896 his machines with up to eight discs could be adapted as Roentgen ray generators for radiography and electrotherapy treatments in hospital.
MIAMI BEACH -- Mammography can be used after breast cancer surgery to distinguish surgical sequelae from recurrence of cancer, according to a presentation at the annual meeting of the American Roentgen Ray Society.
MIAMI BEACH -- Computer-aided diagnosis significantly improves physician detection of polyps using CT colonoscopy, especially for less experienced doctors, according to a study presented at the annual meeting of the American Roentgen Ray Society.
Priscilla Slanetz reported during the annual meeting of the American Roentgen Ray Society.