• WordNet 3.6
    • n radioactivity the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay
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Century Dictionary and Cyclopedia
  • Interesting fact: The little bags of netting for gas lanterns (called 'mantles') are radioactive, so much so that they will set off an alarm at a nuclear reactor.
    • n radioactivity The property possessed by certain substances of spontaneously emitting obscure rays of a nature distinct from the ether-waves of ordinary radiation. The radiation from radioactive substances does not affect the retina directly, but it has the power of ionizing gases, of discharging electrified bodies, of affecting photographic plates, of exciting fluorescence and phosphorescence, and of producing certain chemical and physiological results. It is by means of these effects that the existence of this type of radiation has been discovered and that the properties of the obscure rays from radioactive substances have been investigated. Radioactivity appears to be a property common to the elements uranium, thorium, radium, polonium, and actinium, and to their compounds. It was first detected in 1896 by Becquerel who discovered that when compounds of uranium were placed in the neighborhood of a photographic plate, completely protected from the direct action of light, the plate was acted upon, and that the photographic action occurred even though a thin layer of metal was placed between the radioactive substances and the sensitive film. In the search for similar properties in other substances, Mme. Curie, and independently Schmidt, discovered that the element thorium and its compounds were radioactive, and it was further observed by Mme. Curie that certain minerals containing nranium possessed this property in a higher degree than uranium itself. The extraordinary activity of pitchblende led to the study of this mineral with a view to the separation of the substance to which this property was due, and to the discovery, by M. and Mme. Curie, of a new element, radium, the compounds of which are more than a million times as active as uranium. The most delicate method for the detection of radioactivity depends upon the power of the rays to render air a conductor of electricity and thus to discharge electrified bodies. By means of the rate of discharge, as measured by a sensitive electrometer, the radioactivity of different substances can quantitatively be compared and a degree of radioactivity as intense as that of uranium can be detected. By this means radium has been shown to be a widely distributed element, present in minute quantities in rocks, soils, and waters in various parts of the world. The rays from radium have been divided into three types, the α-, β-, and γ-rays. (See obscure rays.) The kinetic energy of the α-rays is very great, and since they are readily absorbed even by the surrounding air, there is a constant development of heat sufficient to cause the radioactive material to maintain itself at a temperature appreciably higher than that of its surroundings. The β-rays emitted by radium are capable of passing through thin layers of metal. They are strongly deflected from their path by the action of a magnet. The β-rays are supposed to consist of a stream of negatively charged particles or electrons. The γ-rays have an extraordinary penetrating power, being capable of passing through several centimeters of metal. Like the α- and β-rays, they produce photographic effects and also fluorescence and phosphorescence. They are not deflected from their course in the magnetic field. In addition to the emission of obscure rays, radioactive substances are autoluminescent (see luminescence) and shine in the dark with a faint fluorescent light, which, unlike the luminescence of other substances, is independent of external excitation. The phenomenon is observable, however, only in the case of compounds of considerable purity, in which the radioactivity is very intense. The radioactive elements possess the remarkable property of undergoing spontaneous disintegration. The first disintegration-product of radium is a radioactive gas termed the emanation (see emanation, 5), which possesses the property of imparting to surrounding objects a temporary radioactivity, due to the production and deposition of a series of further disintegration-products known as radium A, radium B, radium C, etc., which are solids. Thorium and actinium produce intensely radioactive non-volatile substances which have been designated by the terms thorium X and actinium X; and from these, emanations called thorium emanation and actinium emanation have their source. No gaseous emanation from uranium has as yet been discovered. The thorium emanation and the actinium emanation, however, like that of radium, are found to produce spontaneously a series of further active non-gaseous disintegration-products, thorium A, B, and C, and actinium A, B, and C. The rate at which these transformations take place appears to be an inherent property of the respective substances and incapable of being retarded, hastened, or in any way modified by external means, or effected by the state of chemical combination. The obscure rays from radioactive substances are also capable of producing certain chemical changes, such as the decomposition of water and the conversion of ordinary phosphorus into the red variety. The rays from radium appear to facilitate oxidation. The radiation from strong preparations of radium affects the skin, producing serious burns, and if such a radioactive compound is brought near the head a sensation of light is produced even though the eyes be closed. The temporary radioactivity produced on the surface of objects in contact with an emanation is variously called excited radioactivity, induced radioactivity, and imparted radioactivity.
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In literature:

If there's any radioactivity there, it's not very much.
"The Lani People" by J. F. Bone
The periods of most of the radioactive substances have been calculated, that of uranium being very long.
"Q. E. D., or New Light on the Doctrine of Creation" by George McCready Price
Water systems might be affected somewhat by radioactive fallout, but the risk would be small, especially if a few simple precautions were taken.
"In Time Of Emergency" by Department of Defense
Another product of radioactive origin is lead.
"The Birth-Time of the World and Other Scientific Essays" by J. (John) Joly
The study of these radioactive elements has led to a new atomic theory.
"Creative Chemistry" by Edwin E. Slosson
By F. SODDY, Lecturer in Physical Chemistry and Radioactivity, University of Glasgow.
"Anthropology" by Robert Marett
The craters would be highly radioactive, and some radioactive debris was certain to be scattered around, too.
"Rip Foster in Ride the Gray Planet" by Harold Leland Goodwin
Once he put his hand out toward the spool, then jerked it back as though the thing were radioactive.
"Time Crime" by H. Beam Piper
He knew, then, that nothing but incandescent, radioactive gas remained of the other ship and its crew.
"Space Tug" by Murray Leinster
With many of the vital parts aboard the crashed freighters still hot with radioactivity, the crew had to improvise.
"The Space Pioneers" by Carey Rockwell

In news:

Both radioactive and political fallout from the Chernobyl reactor disaster have now soaked deep into the American grass roots.
Millions of pounds of highly radioactive reactor fuel have been sitting in Energy Department storage pools for so long that they are rusting and spreading radioactivity, the Energy Department said today.
I hope this isn't radioactive.
Let's stipulate that British Petroleum is about as radioactive as any company could be right now because of the Gulf oil spill.
EPA and USDA are monitoring food, rain, and potable water for levels of radioactivity that may have drifted to the United States from Japan.
More radioactive water spills at Japan nuke plant.
The levels of radioactivity were still well below United States and Japanese safety limits.
Radioactive boars in Germany a legacy of Chernobyl.
In an unrelated matter, it's being reported that radioactive snow is falling in Japan.
Small radioactive disc found in old science kit at Burlington high school.
A radioactive issue in Virginia.
Great Lakes are no place for radioactive cargo .
Yasser Arafat and the Radioactive Cigarette .
Between shitty tequila and radioactive-green ready-made mix, frozen margaritas are usually a recipe for disaster.
NEW YORK (AP) — Scientist and activist Barry Commoner, who raised early concerns about the effects of radioactive fallout and was one of the pioneers of the environmental movement, has died at age 95.

In science:

It is also worth remarking that increasing the trigger threshold reduces the contribution of the noise and permits detection of a high-energy a-band from a 241Am radioactive source (see Fig. 4).
Proceedings of the 1st International Workshop "Radiopure Scintillators for EURECA" (RPScint'2008)
As it was demonstrated recently, recrystallization can decrease radioactive contamination of CaWO4 crystals one order of magnitude .
Proceedings of the 1st International Workshop "Radiopure Scintillators for EURECA" (RPScint'2008)
Danevich et al., “Effect of recrystallization on the radioactive contamination of CaWO4 crystal scintillators” (in preparation). 21. F.A.
Proceedings of the 1st International Workshop "Radiopure Scintillators for EURECA" (RPScint'2008)
We performed both cosmic-ray and radioactive source (60Co) runs.
A prototype liquid Argon Time Projection Chamber for the study of UV laser multi-photonic ionization
In addition, a second set of cosmic-ray and radioactive source (60Co) runs were performed.
A prototype liquid Argon Time Projection Chamber for the study of UV laser multi-photonic ionization