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."


(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.

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.

cosmic rays

ionizing irradiation from outer space bombarding the earth and its atmosphere. They contribute to the background radiation that is always present at the earth's surface.
References in periodicals archive ?
The Super-Kamiokande facility, operated by the university's Institute of Cosmic Ray Research, was damaged in November when a chain reaction destroyed most of the photomultiplier tubes installed in the system.
Most cosmic rays are the nuclei of atoms that have been accelerated to very high velocities--and therefore energies--by exploding stars or powerful magnetic fields in space.
Our main goal is to understand the origins of these rare cosmic rays, in order to gain a better understanding of some of the most violent processes shaping the universe.
html) 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.
Caption: Scientists at the Netherlands' LOFAR observatory have developed a technique using cosmic rays that may help expose the conditions inside thunderclouds that lead to lightning strikes.
Korff, then in his early 30s, cosmic rays became a lifelong pursuit.
They found a small correlation between cosmic rays and global temperatures occurring every 22 years; however, the changing cosmic ray rate lagged behind the change in temperatures by between one and two years, suggesting that the cause may not be down to cosmic rays and cloud formation, but may be due to the direct effects of the Sun.
Scientists have been trying to find the sources of high-energy cosmic rays since their discovery a century ago," said Elizabeth Hays, a member of the research team and Fermi deputy project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.
A prominent theory holds that this breakdown is sparked by a cosmic ray, part of the constant rain from space, striking an air molecule and kicking out a high- speed electron left in the atmosphere after a normal lightning bolt.
For his discovery, Anderson was awarded the Nobel Prize for physics in 1936, sharing it with Hess, who had discovered cosmic rays (see 1911).
gov/image-feature/goddard/cream-selected-for-iss) what gives cosmic rays the energy they have and whether they're accelerated by a single cause or not.
Objective: The origin of cosmic rays remains one of the largest mysteries in astrophysics.