- 1. A beam of light, heat, or other form of radiation. The rays from radium and other radioactive substances are produced by a spontaneous disintegration of the atom; they are electrically charged particles or electromagnetic waves of extremely short wavelength. 2. A part or branch that extends radially from a structure. [L. radius]- actinic r. a light r. toward and beyond the violet end of the spectrum that acts upon a photographic plate and produces other chemical effects. SYN: chemical r..- anode rays those originating in a gas discharge tube and moving in a direction opposite to that of cathode rays; made up of positively charged ions. SYN: positive rays.- Becquerel rays obsolete term for radiation given off by uranium and other radioactive substances; these include α, β, and γ rays.- cathode rays a stream of electrons emitted from the negative electrode (cathode) in a Crookes tube; their bombardment of the anode or the glass wall of the tube gives rise to x-rays.- cosmic rays high-velocity particles of enormous energies, bombarding earth from outer space; the “primary radiation” consists of protons and more complex atomic nuclei that, on striking the atmosphere, give rise to neutrons, mesons, and other less energetic “secondary radiation.”- direct rays SYN: primary rays (2).- gamma rays electromagnetic radiation emitted from radioactive substances; they are high-energy x-rays but originate from the nucleus rather than the orbital shell and are not deflected by a magnet.- glass rays those formed by cathode rays striking the wall of an x-r. tube; a special case of indirect rays and soft x-rays. Obsolete.- grenz r. (grents) very soft x-rays, closely allied to the ultraviolet rays in their wavelength ( i.e., relatively long) and in their biologic action upon tissues; they are produced by a specially built vacuum tube with a hot cathode operating from a transformer delivering not more than 8 kw. [Ger. Grenze, borderline, boundary]- hard rays rays of short wavelength and great penetrability.- medullary r. the center 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. SYN: Ferrein pyramid, pars radiata lobuli corticalis renis, processus ferreini.- primary rays 1. cosmic rays in the form in which they first strike the atmosphere; 2. x-rays generated at the focal spot of the tube. SYN: direct rays.- reflected r. a r. of light or other form of radiant energy which is thrown back from a nonpermeable or nonabsorbing surface; the r. which strikes the surface before reflection is the incident r..- roentgen r. SYN: x-r. (1).- soft rays x-rays of relatively long wavelength and slight penetrability.- supersonic rays rays with a wavelength higher than that perceptible to the human ear, above 20,000 Hz.- W rays SYN: intermediate rays.- x-r. x-r..
* * *ray 'rā n any of numerous elasmobranch fishes (order Hypotremata) having the body flattened dorsoventrally, the eyes on the upper surface, and a much-reduced caudal region having typically a slender process often with venomous spinesray n1) one of the lines of light that appear to radiate from a bright object2) a beam of radiant energy (as light) of small cross section3 a) a stream of material particles traveling in the same line (as in radioactive phenomena)b) a single particle of such a streamrayed 'rād adj
* * *(ra) [L. radius spoke] 1. a line emanating from a center. 2. a distinct portion of electromagnetic radiation that proceeds in a specific direction. 3. any of various marine elasmobranch fishes with flattened bodies and narrow tails. See also stingray.
Medical dictionary. 2011.