half-life(redirected from t - ½)
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1. Physics The time required for half the nuclei in a sample of a specific isotopic species to undergo radioactive decay.
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.
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)
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.
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.
The 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.
1. 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.
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|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)|
1. n. vida media, tiempo requerido para que la mitad de una sustancia ingerida o inyectada en el organismo se elimine por medios naturales;
2. semidesintegración, tiempo requerido por una sustancia radioactiva para perder la mitad de su radioactividad por desintegración.