half-life

American  

[haf-lahyf] / ˈhæfˌlaɪf /

Or half life,

noun

half-lives plural

1. Physics. the time required for one half the atoms of a given amount of a radioactive substance to disintegrate.

2. Also called biological half-life.  Pharmacology. the time required for the activity of a substance taken into the body to lose one half its initial effectiveness.

3. Informal. a brief period during which something flourishes before dying out.

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half-life British  

noun

1.  τ.  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 )

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half-life Scientific  

/ hăf′līf′ /

1. 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.

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half-life Cultural  

1. 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.

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Discover More

Scientists can estimate the age of an object, such as a rock, by carefully measuring the amounts of decayed and undecayed nuclei in the object. Comparing that to the half-life of the nuclei tells when they started to decay and, therefore, how old the object is. (See radioactive dating.)

Other Word Forms

Noun Inflected Forms

• half-lives
  plural

Etymology

Origin of half-life

First recorded in 1905–10; half + life

Example Sentences

Its subsequent cultural half life has been limited, too; those few elements which have lingered illustrate perfectly why it was not renewed.

From New York Times • Jan. 27, 2024

The key radioactive atom in the plutonium pit has a half life of 24,000 years, which is the amount of time it would take roughly half of the radioactive atoms present to decay.

From Seattle Times • Sep. 19, 2023

It matters because of the implications for Rishi Sunak - the half life of Boris Johnson is proving rather lengthy.

From BBC • Jun. 19, 2023

U-235 has a half life of about 700 million years and represents about 0.72% of natural uranium.

From Salon • Jun. 17, 2023

The second Maddy knows that this pale half life is not really living.

From "Everything, Everything" by Nicola Yoon