emanation

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The act or an instance of emanating.
2. n. Something that issues from a source; an emission.
3. n. Chemistry Any of several radioactive gases that are isotopes of radon and are products of radioactive decay.

Century Dictionary and Cyclopedia

1. n. The act of flowing or issuing from a fountainhead or origin; emission; radiation.
2. n. In philosophy: Efficient causation due to the essence and not to any particular action of the cause. Thus, when the trunk of a tree is moved, the branches go along with it by virtue of emanation. Hence — The production of anything by such a process of causation, as from the divine essence. The doctrine of emanation appears in its noblest form in the Enneads of Plotinus, who makes sensible things to emanate from the Ideas, the Ideas to emanate from the Nous, and the Nous to emanate from the One. Iamblichus makes the One to emanate from the Good, thus going one step further. The Gnostics and Cabalists pushed the doctrine to fantastic developments.
3. n. That which issues, flows, or is given out from any substance or body; effiux; effiuvium: as, the odor of a flower is an emanation of its particles.
4. n. In algebra, the process of obtaining the successive emanants of a quantic.
5. n. Specifically, in radioactivity, an unstable gaseous disintegration-product spontaneously produced from a radioactive substance. The radioactive elements thus far known to give off an emanation are thorium, radium, and actinium. The emanations are inert gases resembling in their chemical relations the gases of the argon group, but differing from these and from all other known chemical compounds in the fact that they are produced as disintegration-products continuously at a rate which is independent of the temperature and the chemical and physical state of the compounds from which they are formed and which are converted spontaneously into other and non-volatile disintegration-products at a constant rate. The existence of an emanation, which is produced only in very small quantities, is detected by means of its radioactive effects. The rate at Which it is produced and at which it disappears by disintegration is determined from the change in the intensity of these effects, and it is by such observations that the emanations of radium, thorium, and actinium are distinguished from one another. The radium emanation differs from the others in that it is the first disintegration-product of that element, whereas with thorium and actinium the emanation in the case of the former is the fifth, and in the case of the latter the third, disintegration-product to be produced. These three emanations differ greatly in the degree of instability which they exhibit. The rate of decay (which measures the rate at which the radium emanation is converted into the next following and non-volatile disintegration-product) is comparatively slow, about 3.7 days being required to reduce its activity to one half; whereas the thorium emanation suffers the corresponding reduction in about one minute and the actinium emanation in 3.9 seconds. The properties of the emanations, which are in the main, similar, have been most completely studied in the case of radium emanation. Its chemical inertness is shown by the fact that it will pass through tubes containing reagents which absorb all gases except those of the argon family, that it is unaffected by the electric spark in an atmosphere of oxygen, and that it may be kept in contact with incandescent magnesium or calcium for hours without loss. Both radium emanation and thorium emanation are capable of condensation at low temperatures, the point of liquefaction of the thorium emanation being—120° C. and that of the radium emanation —150° C. All three emanations are radioactive, giving off α-rays, and they possess the property of imparting temporary radioactivity to all substances with which they come in contact. This imparted radioactivity disappears much more slowly than the emanation itself, having its own law of decay, and the imparted radioactivity is of the same character, whatever the nature of the substance affected. The imparted radioactivity, or excited radioactivity, is ascribed to the formation, on the surface of the body made active, of a solid disintegration-product; and it has been found possible to remove this product by rubbing the surface with sandpaper, and to transfer the activity to the latter. The radioactive matter can also be dissolved by certain acids. However, it is not destroyed, but reappears on the surface of the dish after the acid has been evaporated. Thus it appears that a film of radioactive matter is deposited upon surfaces with which the emanation comes in contact, and that this active deposit consists of a series of successive disintegration-products of the emanation. A series of changes of this sort has been traced, and the successive disintegration-products, which differ as regards their stability and radioactive character, have been studied. They are known respectively as radium A, radium B, radium C, radium D, radium E, radium F, radium G; thorium A, thorium B, thorium C; and actinium A, actinium B, and actinium C. These disintegration-products behave as solids, being in general volatilized at a white heat They are soluble in strong acids, and separable from one another by electrolysis. Each disintegration-product is spoken of as the parent at the one which it produces, and the first of the series is known as the parent substance. In most of these changes in radioactive bodies rays are emitted; but certain changes (known as rayless changes) unaccompanied by radiation have been recognized. The emission of β-rays and γ-rays appears to be characteristic of the last of the succession of changes to which the radioactive elements are subject, and to result in the appearance of a product more stable than those which have gone before.

Wiktionary

1. n. The act of flowing or proceeding from a fountain head or origin.
2. n. That which issues, flows, or proceeds from any object as a source; efflux; an effluence; as, perfume is an emanation from a flower.
3. n. uncountable, obsolete, chemistry radon

GNU Webster's 1913

1. n. The act of flowing or proceeding from a fountain head or origin.
2. n. That which issues, flows, or proceeds from any object as a source; efflux; an effluence.

WordNet 3.0

1. n. (theology) the origination of the Holy Spirit at Pentecost
2. n. the act of emitting; causing to flow forth
3. n. something that is emitted or radiated (as a gas or an odor or a light, etc.)