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half-life
[ haf-lahyf ]
noun
- Physics. the time required for one half the atoms of a given amount of a radioactive substance to disintegrate.
- Also called bi·o·log·i·cal half-life [bahy, uh, -, loj, ik, uh, l , haf, -lahyf]. Pharmacology. the time required for the activity of a substance taken into the body to lose one half its initial effectiveness.
- Informal. a brief period during which something flourishes before dying out.
half-life
noun
- the time taken for half of the atoms in a radioactive material to undergo decay τ
- 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
/ 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-life
- In physics , a fixed time required for half the radioactive nuclei in a substance to decay. Half-lives of radioactive substances can range from fractions of a second to billions of years, and they are always the same for a given nucleus, regardless of temperature or other conditions. If an object contains a pound of a radioactive substance with a half-life of fifty years, at the end of that time there will be half a pound of the radioactive substance left undecayed in the object. After another fifty years, a quarter-pound will be left undecayed, and so on.
Notes
Word History and Origins
Origin of half-life1
Example Sentences
The half-life of a piece of technology these days is very short.
But the half-life of a piece of hardware is very short these days.
Radiation dissipates over time with every isotopic half-life.
It was a small picture, half life-size, and set in an oval frame of black walnut.
A very beautiful marble group, half life-size, stood in one corner, and gave an air of brightness to the whole room.
Now the old problem of half-life is taking its toll, and we cant even hope to keep up with the birth rate any more.
And, finally, Moglaut had warned that the compact power unit pocketed on the left breast had a half-life of only thirteen years.
Then he knew all hope was over, and the mad passion went out of him, and his arms dropped to his sides as if half life had fled.
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