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half-life
half-life (hăf′līf′, häf′-)n.1. Physics The time required for half the nuclei in a sample of a specific isotopic species to undergo radioactive decay.2. Biology a. The time required for half the quantity of a drug or other substance deposited in a living organism to be metabolized or eliminated by normal biological processes. Also called biological half-life.b. The time required for the radioactivity of material taken in by a living organism to be reduced to half its initial value by a combination of biological elimination processes and radioactive decay.half-life n 1. (General Physics) the time taken for half of the atoms in a radioactive material to undergo decay. Symbol: τ 2. (Biology) 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) half′-life` or half′ life`,
n., pl. -lives (-ˌlaɪvz) 1. the time required for one half the atoms of a given amount of a radioactive substance to decay. 2. the time required for the activity of a substance taken into the body to lose one half its initial effectiveness. [1905–10] half-life (hăf′līf′) The average time needed for half the nuclei in a sample of a radioactive substance to undergo radioactive decay. The half-life of a substance does not equal half of its full duration of radioactivity. For example, if one starts with 100 grams of radium 229, whose half-life is 4 minutes, then after 4 minutes only 50 grams of radium will be left in the sample, after 8 minutes 25 grams will be left, after 12 minutes 12.5 grams will be left, and so on.half-lifeThe time required for the activity of a given radioactive species to decrease to half of its initial value due to radioactive decay. The half-life is a characteristic property of each radioactive species and is independent of its amount or condition. The effective half-life of a given isotope is the time in which the quantity in the body will decrease to half as a result of both radioactive decay and biological elimination.half-life1. A substance which undergoes exponential decay decays by the same ratio in equal intervals of time. The constant ratio is the half-life. The rate of radioactive decay of a substance is defined by its half-life.2. The time in which half the atoms in a radioactive isotope decay.Thesaurus| Noun | 1. | half-life - the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)half lifeperiod, period of time, time period - an amount of time; "a time period of 30 years"; "hastened the period of time of his recovery"; "Picasso's blue period" |
Translationshalf-life
half-life, measure of the average lifetime of a radioactive substance (see radioactivityradioactivity,
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.
..... Click the link for more information. ) 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
or radioisotope,
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.
..... Click the link for more information. 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-life1. 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) half-life
Half-lifeThe point in the life of a mortgage-backed security guaranteed or issued by the Government National Mortgage Association, the Federal National Mortgage Association or the Federal Home Loan Mortgage Corporation when half the principal has been repaid.Half LifeIn a pool of mortgages underlying a mortgage-backed security, the length of time it takes for half the aggregate principal to be repaid. A half life is normally about 12 years, but this may vary depending on how often homeowners refinance their mortgages (which pays off all principal at once). Half lives are calculated for mortgage-backed securities issued or guaranteed by Freddie Mac, Fannie Mae, and Ginnie Mae.
Weighted Average LifeThe amount of time for the principal on a loan or a mortgage to be paid off. The length of the weighted average life depends on the amount of principal paydowns and how often they are made. Once the WAL is calculated, one can determine how long it will take to pay off half of the remaining principal.half-life The length of time before half the principal on a debt is expected to be repaid through amortization or sinking fund payments. For example, a 25-year bond issue may require the issuer to retire 5% of the beginning principal commencing 5 years after the issue date. Thus, the bond issue has a half-life of 5 years plus the number of years required to retire half the issue, or 15 years. Mortgage-backed securities often have a relatively short half-life because many homeowners pay off or refinance their mortgages early. Also called average life.half-life
Synonyms for half-lifenoun the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)SynonymsRelated Words- period
- period of time
- time period
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