half-life

or half life, half·life

[ haf-lahyf, hahf- ]

/ ˈhæfˌlaɪf, ˈhɑf- /

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noun, plural half-lives

[haf-lahyvz, hahf-]. /ˈhæfˌlaɪvz, ˈhɑf-/.

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

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.

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

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THINGAMABOB OR THINGUMMY: CAN YOU DISTINGUISH BETWEEN THE US AND UK TERMS IN THIS QUIZ?

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Question 1 of 7

In the UK, COTTON CANDY is more commonly known as…

candystring

candyfloss

candypuff

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Also called half-life period.

Origin of half-life

First recorded in 1905–10; half + life

Words nearby half-life

half-joking, half landing, half-lap joint, half-leather, half-length, half-life, half-light, half-line, halfling, half-liter, half-long

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use half-life in a sentence

The half-life of a piece of technology these days is very short.
ecoATM offers consumers a new way to sell used cell phones and electronic devices|Sarah Langs|September 1, 2013|DAILY BEAST
But the half-life of a piece of hardware is very short these days.
The BlackBerry’s Death Rattle Gets Louder|Daniel Gross|August 12, 2013|DAILY BEAST
Radiation dissipates over time with every isotopic half-life.
Radioactive Tuna Won’t Kill You—but Should We Be Concerned About Mercury?|Daniel Stone|May 30, 2012|DAILY BEAST
It was a small picture, half life-size, and set in an oval frame of black walnut.
Theo|Mrs. Frances Hodgson Burnett

A very beautiful marble group, half life-size, stood in one corner, and gave an air of brightness to the whole room.
Dr. Jolliffe's Boys|Lewis Hough
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.
They Also Serve|Donald E. Westlake
And, finally, Moglaut had warned that the compact power unit pocketed on the left breast had a half-life of only thirteen years.
Zero Data|Charles Saphro
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.
Beyond The Rocks|Elinor Glyn

British Dictionary definitions for half-life

half-life

noun

the time taken for half of the atoms in a radioactive material to undergo decaySymbol: 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)

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for 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.

Cultural definitions for half-life

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 for half-life

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.)