radiation (redirected from Radiation exposure)

radiation (rā'dēā`shən), term applied to the emission and transmission of energy through space or through a material medium and also to the radiated energy itself. In its widest sense the term includes electromagnetic, acoustic, and particle radiation, and all forms of ionizing radiation. Commonly radiation refers to the electromagnetic spectrum, which, in order of decreasing wavelength, includes radio, microwave, infrared, visible-light, ultraviolet, X-ray, and gamma-ray emissions. All of these travel through space at the speed of light (c.300,000 km/186,000 mi per sec) but differ in wavelength and frequency. According to the quantum theory, the energy carried in the form of electromagnetic radiation may be viewed as made up of tiny bundles or packets, each bundle being known as a photon. The sun is the source of much radiant energy in the form of sunlight and heat. Heat radiation is infrared radiation. All types of electromagnetic radiation can be reflected and absorbed in the same manner as is visible light. Acoustic radiation, propagated as sound waves, may be sonic (in the frequency range from 16 to 20,000 cycles per sec), infrasonic, or subsonic (frequency less than 16 cycles per sec), and ultrasonic (frequency greater than 20,000 cycles per sec). Examples of particle radiation are alpha and beta rays in radioactivity, and many kinds of atomic and subatomic particles such as electrons, mesons, neutrons, protons, and heavier nuclei (see cosmic rays). Radiation is usually considered to travel from a source in straight lines, but its path may be affected by external factors; for instance, charged particles travel in curved paths in magnetic fields. The Van Allen radiation belts consist of charged particles trapped in the earth's magnetic field.

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radiation

Process by which energy is emitted from a source and propagated through the surrounding medium, or the energy involved in this process. Radiation consists of a flow of atomic or subatomic particles or of waves. Familiar examples are light (a form of electromagnetic radiation) and sound (a form of acoustic radiation). Both electromagnetic and acoustic radiation can be described as waves with a range of frequencies and intensities. Electromagnetic radiation is also often treated as discrete packets of energy, called photons. All matter is constantly bombarded by radiation from cosmic and terrestrial sources, and radioactive elements emit several types of radiation (see radioactivity). See also Cherenkov radiation, Hawking radiation, infrared radiation, synchrotron radiation, thermal radiation, ultraviolet radiation.

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radiation

1. Physics

a. the emission or transfer of radiant energy as particles, electromagnetic waves, sound, etc.

b. the particles, etc., emitted, esp the particles and gamma rays emitted in nuclear decay

2. Med treatment using a radioactive substance

3. Anatomy a group of nerve fibres that diverge from their common source

4. See adaptive radiation

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radiation [‚rād·ē′ā·shən]

(engineering)

A method of surveying in which points are located by knowledge of their distances and directions from a central point.

(physics)

The emission and propagation of waves transmitting energy through space or through some medium; for example, the emission and propagation of electromagnetic, sound, or elastic waves.

The energy transmitted by waves through space or some medium; when unqualified, usually refers to electromagnetic radiation. Also known as radiant energy.

A stream of particles, such as electrons, neutrons, protons, α-particles, or high-energy photons, or a mixture of these.

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Radiation

The emission and propagation of energy; also, the emitted energy itself. The etymology of the word implies that the energy propagates rectilinearly, and in a limited sense, this holds for the many different types of radiation encountered.

The major types of radiation may be described as electromagnetic, acoustic, and particle, and within these major divisions there are many subdivisions. Electromagnetic radiation is classified roughly in order of decreasing wavelength as radio, microwave, visible, ultraviolet, x-rays, and γ-rays. Acoustic or sound radiation may be classified by frequency as infrasonic, sonic, or ultrasonic in order of increasing frequency, with sonic being between about 16 and 20,000 Hz. The traditional examples of particle radiation are the α‒ and β-rays of radioactivity. See Electromagnetic radiation, Radioactivity, Sound

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radiation

The transmission of heat through space by means of electromagnetic waves; the heat energy passes through the air between the source and the heated body without heating the intervening air appreciably.