cosmic rays

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cos·mic 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."
Farlex Partner Medical Dictionary © Farlex 2012


(ra) [Fr. rai, raie, fr L. radius, ray]
1. Any of several lines diverging from a common center.
2. A line of propagation of any form of radiant energy, esp. light or heat; loosely, any narrow beam of light.

actinic ray

A solar ray capable of producing chemical changes. Synonym: chemical ray

alpha ray

A ray composed of positively charged helium particles derived from atomic disintegration of radioactive elements. Its velocity is one tenth the speed of light. Alpha rays are completely absorbed by a thin sheet of paper and possess powerful fluorescent, photographic, and ionizing properties. They penetrate tissues less than beta rays.

beta ray

A ray composed of negatively charged electrons expelled from atoms of disintegrating radioactive elements.
Synonym: beta particle

border ray

Grenz ray.

cathode ray

A ray composed of negatively charged electrons discharged by a cathode through a vacuum, moving in a straight line and producing x-ray photons upon hitting solid matter.

central ray

The theoretical center of an x-ray beam. The term designates the direction of the x-ray photons as projected from the focal spot of the x-ray tube to the radiographical film.

characteristic ray

A secondary photon produced by an electron giving up energy as it changes location from an outer to an inner shell in an atom. The wavelengths are characteristic of the difference in binding energies.

chemical ray

Actinic ray.

cosmic rays

Cosmic radiation.

delta rays

Highly penetrative waves emitted by radioactive substances.

erythema-producing ray

Ultraviolet radiation (wavelengths between 2050 and 3100 A.U.) capable of reddening skin.

gamma rays

Short wavelength, high-energy electromagnetic radiation emitted by disintegrating atomic nuclei.

grenz ray

A low-energy x-ray photon with an average wavelength of 2 A.U. (range from 1 to 3 A.U.); obtained with peak voltage of less than 10 kV. Grenz rays lie between ultraviolet and x-rays.
Synonym: border ray

hard ray

An x-ray photon of short wavelength and great penetrative power.

heat ray

Radiation whose wavelength is between 3,900 and 14,000 A.U. Shorter wavelength heat sources penetrate tissues better than longer (infrared) sources.
See: heat

infrared ray

An invisible heat ray from beyond the red end of the spectrum. Infrared wavelengths range from 7700 angstrom units (A.U.) to 1 mm. Long-wave infrared rays (15,000 to 150,000 A.U.) are emitted by all heated bodies and exclusively by bodies of low temperature such as hot water bottles and electric heating pads; short-wave infrared rays (7,200 to 15,000 A.U.) are emitted by all incandescent heaters. The sun, electric arcs, incandescent globes, and so-called infrared burners are sources of infrared rays.


Infrared ray energy is transformed into heat in a superficial layer of the tissues. It is used therapeutically to stimulate local and general circulation and to relieve pain. The infrared thermograph is useful in studying the heat of tissues. See: radiation; thermography

luminous ray

One of the visible rays of the spectrum.

medullary ray

In the kidney, one of many slender processes composed of one or two collecting ducts and other straight tubules that project into the cortex from the bases of renal pyramids.

monochromatic ray

Single wavelength electromagnetic radiation.

pigment-producing ray

A ray between 2540 and 3100 A.U. that is most effective in stimulating pigment production in the skin. This is due to a local response to irritation of cutaneous prickle cells.

positive ray

A ray composed of positively charged ions that in a discharge tube moves from the anode toward the cathode.

primary ray

In radiographic imaging, the x-ray beam that originates at the source of radiation. It is usually used to differentiate those rays from the additional scatter radiation that constitutes the majority of the beam used to create images.

roentgen ray

X-ray photon.

scattered ray

See: radiation

secondary rays

X-ray photons produced after the incoming, primary x-ray photons remove an inner-shell electron from the atom. Secondary rays can also be primary x-rays that have been diverted through scatter interactions with other atoms. Secondary rays are of lower energy than primary rays and are usually absorbed in matter, an interaction that produces x-ray photons via a cascade effect.

ultraviolet ray

An invisible ray of the spectrum beyond the violet rays. The wavelengths of ultraviolet rays vary. They may be refracted, reflected, and polarized, but will not traverse many substances impervious to the rays of the visible spectrum. They rapidly destroy the vitality of bacteria, and are able to produce photochemical and photographic effects.
Medical Dictionary, © 2009 Farlex and Partners

cosmic rays

a stream of atomic particles entering the earth's atmosphere from outer space at nearly the speed of light. Cosmic rays are thought to be a cause of SPONTANEOUS MUTATIONS.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
References in periodicals archive ?
Physicist Sam Ting spent years lobbying to put a cosmic ray detector aboard the International Space Station.
Looking at contributions from galactic cosmic rays, secondary particles, and sensor background, they were able to derive energy spectra for the radiation dose that humans or instruments would absorb in the lunar environment.
Cosmic rays are subatomic particles that move through space at almost the speed of light.
Twenty-four segmented telescopes watch the skies for faint streaks of ultraviolet fluorescence produced when nitrogen atoms are ionized by an incoming cosmic ray. Meanwhile, 1,600 ground-level detectors --instrumented tanks of purefied water--detect "air showers" of secondary particles (mostly gamma rays and electrons) that are spawned when a high-energy cosmic ray collides with an atom in the top of the atmosphere.
To illustrate that in terms that are relatively easy for laypersons to understand, Michigan Technological University (MTU) said in ( a statement Thursday: "It's extremely rare for cosmic rays with energy greater than two joules to reach Earth; the rate of their arrival at the top of the atmosphere is only about one per square kilometer per year, the equivalent to one cosmic ray hitting an area the size of a soccer field about once per century."
Researchers hope that AMS can bring clarity to this debate because of its leg up on other cosmic ray detectors.
The detector provides high-precision measurements of cosmic ray particle fluxes, their ratios and gamma rays.
As a result, even low-energy cosmic rays can reach the surface, turning the Moon into a handy space-based particle detector.
It's a cosmic ray hit," Doug Ellison, visualization producer at NASA's Jet Propulsion Laboratory, explained over ( Twitter .
The question arises: what energy could be cosmic rays, if the distance between the source and the Earth would be much less than the Greisen-Zatsepin-Kuzmin limit, and could not microparticle produce a huge macroscopic effect?
Special detectors recorded by-products of the cosmic ray known as muons that are only partially absorbed by stone and take noticeably different trajectories through air.
Lead scientist Professor Gregory Snow, from the University of Nebraska-Lincoln in the US, said: "There have been other pieces of evidence, but I would say this paper really confirms that most of the highest energy cosmic ray particles are not coming from the Milky Way.