half-life

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half-life,

spontaneous disintegration or decay of the nucleus of an atom by emission of particles, usually accompanied by electromagnetic radiation. The energy produced by radioactivity has important military and industrial applications.
) or an unstable subatomic particle. One half-life is the time required for one half of any given quantity of the substance to decay. For example, the half-life of a particular radioactive isotoperadioactive isotope
natural or artificially created isotope of a chemical element having an unstable nucleus that decays, emitting alpha, beta, or gamma rays until stability is reached.
of thorium is 8 minutes. If 100 grams of the isotope are originally present, then only 50 grams will remain after 8 minutes, 25 grams after 16 minutes (2 half-lives), 12.5 grams after 24 minutes (3 half-lives), and so on. Of course the 87.5 grams that are no longer present as the original substance after 24 minutes have not disappeared but remain in the form of one or more other substances in the isotope's radioactive decay series. Individual decays are random and cannot be predicted, but this statistical measure of the great number of atoms in the sample is very accurate. The half-life of a radioactive isotope is a characteristic of that isotope and is not affected by any change in physical or chemical conditions.

half-life

The time taken for the number of atoms of a radioactive isotope to be reduced, by radioactive decay, to one half. The mean life is the average time before decay of a large number of similar elementary particles or atoms of a radioisotope. Mean life is equal to 1.44 times the half-life.

Half-Life

the average time required for the number of radioactive nuclei in a sample of a radioactive substance to be halved. If N0 radioactive nuclei exist at a time t = 0, the number of nuclei N decreases in time according to the law

N = N0eλt

where λ is the disintegration constant. The quantity τ = 1/λ is called the mean life of the radioactive nuclei. The half-life T1/2 is related to λ and τ by the equation

T1/2 = τ 1n 2 = (1n 2)/λ = 0.693/λ

half-life

[′haf ‚līf]
(chemistry)
The time required for one-half of a given material to undergo chemical reactions.
(nucleonics)
The average time interval required for one-half of any quantity of identical radioactive atoms to undergo radioactive decay. Also known as half-value period; radioactive half-life.

half-life

1. the time taken for half of the atoms in a radioactive material to undergo decay.
2. the time required for half of a quantity of radioactive material absorbed by a living tissue or organism to be naturally eliminated (biological half-life) or removed by both elimination and decay (effective half-life)
References in periodicals archive ?
Well, it seems like Laidlaw's as tired of waiting for Half-Life 3 as the rest of us.
Lord Gaben, or as he goes by for regular mortals, Valve CEO Gabe Newell, has mentioned Half-Life 3 over the years but of late he hardly ever brings it up or mentions it.
Although the animal data, molecular weight (about 868), and elimination half-life (about 26 hours) suggest embryo-fetal risk, the high plasma protein binding (99.
Slowly clearing infections, which were defined as a parasite clearance half-life of 5 hours or longer and indicated established resistance, were detected throughout mainland Southeast Asia, but they were not yet common in India or Africa.
Variants have been measured with both increased and decreased receptor binding affinities potentially translating to modulation of albumin half-life.
10 20cm), and (2) recovered DCD concentrations and half-life of DCD at two different DCD application rates (10 v.
These common "double" or "half" concepts provide the motivation for examining half-life properties of learning curves.
Episode Two does mark the return of the lengthy vehicle sequences seen in Half-Life 2.
Follow-up of 24 seropositive infants showed that the half-life of antibody persistence was 35.
AlbudAbs are dAbs that specifically bind to serum albumin and can dramatically enhance the half-life and efficacy of any molecule attached to them.
The company has revised the molecular structure of the material to achieve a luminance efficiency of 9cd/A, 30% higher than the company's existing material, and a brightness half-life of 23,000 hours (a threshold luminance of 1,000cd/m2), 130% longer, in emitting blue light which most affects the display's power consumption and life.
Lingo definition: Half-life is a word used to describe hippie-type skaters.

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