| gamma ray | <radiobiology> Electromagnetic radiation (photons) with energies greater than (roughly) 100 keV (that is, 100,000 electron volts). Gamma radiation frequently accompanies alpha and beta decays, and always accompanies fission. Gamma rays are highly penetrating and are best shielded against using dense materials, such as lead or depleted uranium. (Gamma rays are similar to X-rays, but are generally higher in energy and nuclear in origin.) Gamma rays have wavelengths of 1 nanometre or shorter. These are highly energised, deeply penetrating photons which can be emitted from an atomic nucleus during nuclear fission (the splitting of an atom) and during regular atomic decay (radioactivity). (13 Oct 1997) |
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| gamma ray knife | A beam of high energy X-rays. See: radiosurgery. (05 Mar 2000) |
| panoramic X-ray | <dentistry> An X-ray taken by a machine that rotates around your head to give the orthodontist a picture of your teeth, jaws and other important information. (08 Jan 1998) |
| panoramic X-ray film | In dentistry, a radiograph taken to give a panoramic view of the entire upper and lower dental arch as well as the temporomandibular joints. (05 Mar 2000) |
| ray | <botany> A zygomorphic flower in the family Asteraceae, a radial band of cells traversing the conducting elements in woody stems. Of a compound umbel, one of the first (lower) series of branches of the inflorescence main stem. (09 Oct 1997) |
| ray grass | <botany> A perennial European grass (Lolium perenne). Synonym: rye grass, and red darnel. See Darnel, and Grass. Italian ray, or rye, grass. See Darnel, and Grass. Origin: Etymol. Of ray is uncertain. Source: Websters Dictionary (01 Mar 1998) |
| ray, light | <microscopy> The term applied to the lines perpendicular to the wavefronts of waves of light to indicate their direction of travel in an isotropic medium. Note the wave normal and the ray do not coincide in isotropic media. (05 Aug 1998) |
| ray therapeutics | An obsolete term for radiotherapy. (05 Mar 2000) |
| mass chest X-ray | X-ray screening of large groups of persons for diseases of the lung and heart by means of radiography of the chest. (12 Dec 1998) |
| reflected ray | A ray of light or other form of radiant energy which is thrown back from a nonpermeable or nonabsorbing surface; the ray which strikes the surface before reflection is the incident ray. (05 Mar 2000) |
| reflection X-ray microscopy | <technique> A method of producing enlarged images by means of X rays. In this method the radiation is totally reflected at glancing incidence from polished concave mirrors or from the curved surfaces of single crystals by Bragg reflection. The problem of aberration corrections still limits the resolution obtainable. (05 Aug 1998) |
| cathode ray | <physics> Electrons emitted from the surface of a cathode in a vacuum tube. (16 Mar 1998) |
| cathode ray tube | An evacuated tube containing a beam of electrons which can be deflected to various parts of a fluorescent screen; used in the cathode ray oscilloscope. (05 Mar 2000) |
| pa X-ray | An X-ray picture in which the beams pass from back-to-front (posteroanterior). As opposed to an ap (anteroposterior) film in which the rays pass through the body from front-to-back. (12 Dec 1998) |
| medullary ray | The centre of the renal lobule, which has the shape of a small, steep pyramid, consisting of straight tubular parts; these may be either ascending or descending limbs of the nephronic loop or collecting tubules. Synonym: pars radiata lobuli corticalis renis, Ferrein's pyramid, processus ferreini. (05 Mar 2000) |