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see radonradon
, gaseous radioactive chemical element; symbol Rn; at. no. 86; mass no. of most stable isotope 222; m.p. about −71°C;; b.p. −61.8°C;; density 9.73 grams per liter at STP; valence usually 0. Radon is colorless and the most dense gas known.
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(ĕmənā`shən) [Lat.,=flowing from], cosmological concept that explains the creation of the world by a series of radiations, or emanations, originating in the godhead. It is characteristic of NeoplatonismNeoplatonism
, ancient mystical philosophy based on the doctrines of Plato. Plotinus and the Nature of Neoplatonism

Considered the last of the great pagan philosophies, it was developed by Plotinus (3d cent. A.D.).
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 and of GnosticismGnosticism
, dualistic religious and philosophical movement of the late Hellenistic and early Christian eras. The term designates a wide assortment of sects, numerous by the 2d cent. A.D.
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 and is frequently encountered in Indian metaphysics. In the history of Western thought it has been to some extent, as in Neoplatonism, opposed to the Judeo-Christian conception of creation, in which the eternal God makes all from nothing. To explain the relation of a totally transcendent God to a finite and imperfect world, the belief in emanation denies that God directly created the world but maintains rather that the world is the result of a chain of emergence through emanations. From God (the One, or the Absolute), the one prime principle, flows the divine substance; his own substance never lessens. As the flow proceeds farther from God, however, its divinity steadily decreases. When a stone is dropped into water, the circles ever widening from the point (God) where the stone fell are emanations, becoming fainter and fainter. Emanation never ceases, the whole process moving continuously outward from God. In the 3d cent. A.D., PlotinusPlotinus
, 205–270, Neoplatonist philosopher. A native of Egypt, perhaps of Roman descent, he went to Alexandria c.232 to devote himself to philosophy. For 10 years he was a dedicated disciple of Ammonius Saccas.
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 and other Neoplatonists developed a clear system of emanation. The Neoplatonists ascribed to Plato an emanative concept in his Idea of the Good as being supreme, the lesser ideas being in some way related to the Idea of the Good. The concept, in modified form, influenced the development of medieval Christian theology through the writings of Dionysius the Areopagite.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(Em), a gas consisting of any of the naturally occurring radon isotopes—radon-219 (actinon), radon-220 (thoron), and radon-222 (“true” radon). The element radon itself was previously called radium emanation.



the release of radioactive radon atoms into the atmosphere by solid substances containing radium. The release is due either to diffusion or to the recoil motion of the radon nuclei produced by the alpha decay of the parent radium nuclei. Some of the radon atoms remain embedded in the solid substance and undergo radioactive decay themselves before reaching the surface of the solid. The fraction of radon released into the atmosphere is called emanating power and is usually expressed as a percentage.

Emanating power depends on such factors as the composition and structure of the substance, its specific surface, and its temperature. At room temperature, emanating power ranges from 1 percent or less (for some inorganic salts and glasses, for example) to nearly 100 percent (for such substances as barium hexadecanoate, which contains trace amounts of radium). As a rule, emanation increases with rising temperature.

In geology, emanation is sometimes expressed as the amount of radon released by 1 gram of rock within a certain period of time. Other conditions being equal, the higher the amount of radium in the rock, the greater the emanation. Therefore, the radium content of a rock can be estimated by comparing its emanation with that of a specimen for which the radium content is known.

The measurement of emanation serves as the basis for the emanation method of studying solid substances and for a method of locating radioactive ores and minerals.




in ancient idealist philosophy and particularly in Neoplatonism, the overflowing of the plenitude of absolute being beyond its own boundaries. The term is based on a metaphor frequently used in the Platonic tradition—namely, the image of a spring, which gives rise to a river but is inexhaustible, or of the sun, which emits rays but whose own brightness is never diminished.

In the process of emanation, viewed as the step-by-step descent of the absolute (or “the one”), the multiple world of “the other” is formed—that is, the lower levels of being, such as nous or the soul; on the lowest level is matter, or “nonbeing.” Unlike the theist notion of the “creation of the world” as the volitional act of a personal deity, emanation is understood as an involuntary and impersonal process. All richness of content is deemed to be given at the point of origin of the emanation, so that in the various stages, or levels, of emanation there can be only a successive impoverishment, and finally a return to the source.

A concept that may be contrasted to emanationism is that of the self-motion of the idea, which was developed in the philosophy of Hegel and in classical German idealism; it is distinguished by the notion that a greater wealth of meaning is present at the end of the process than at the beginning. The concept of development or evolution as a gradual ascent is antithetical to emanation.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


(nuclear physics)
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


Any modulated signal (sound or electromagnetic radiation) leaking from a device that may be used to reconstruct information being processed or transmitted by that device. See EMSEC and TEMPEST.
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