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 ?
It is this condition that is satisfied for cosmic rays whose particles relative to their source move with velocities close to the speed of light.
The new system will be used in ICRR's projects both in and outside of Japan, and will help illuminate the mechanisms underlying ultra-high energy phenomena such as where and how high-energy cosmic rays originate and accelerate, through deeper, broader studies of the cosmos.
Astronauts helped by the electrometers of Hess and Kohlhoester measured cosmic ray intensity and confirmed the data about cosmic (extraterrestrial) origin of the rays and about the role of atmosphere in their attenuation.
This means predicting future global warming and sea level rise is not simple, since it also significantly depends on the unpredictability of cosmic ray intensity.
where x--hard cosmic ray flux (HCRF); y--atmospheric pressure values; [[sigma].sub.x], [[sigma].sub.y]--standard deviations; [x.sub.i], [y.sub.i]--observations of variable x, y; [bar.x], [bar.y]--average values of variable x, y; n--data of observations; [F.sup.-1]--inverse cumulative density function of normal [0,1] distribution; [gamma]--probability value.
The number of cosmic rays hitting an embryo is dependent on its size, so that the number of cosmic rays hitting the fetus increases as the fetus enlarges.
Scientists have discovered a previously unidentified nearby source of high-energy cosmic rays.
This radioactive isotope is created when energetic particles in cosmic rays enter the Earth's atmosphere and split atomic nuclei of nitrogen and oxygen.
Totsuka, 59, and Kajita, 42, observed neutrinos generated as cosmic rays crash into Earth's atmosphere at the institute's observatory facility Super-Kamiokande in the town of Kamioka, Gifu Prefecture.
In 1929 the German physicist Walther Wilhelm Georg Franz Bothe (1891-1957) devised a new method of studying cosmic rays. He placed two Geiger counters (see 1908) one above the other and set up a circuit that would record an event only if both counters recorded it virtually simultaneously.
"We know the blast waves of exploded stars can accelerate cosmic ray particles to speeds comparable to that of light, an incredible energy boost," said Kenji Hamaguchi, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and the lead author of the study.