half-life

IPA/ˈhɑːf laɪf/
IPA/ˈhæf laɪf/

half-life — noun

1. the time it takes a radioactive element to lose half its radioactivity through n

1.nounB2
Definition

the time it takes a radioactive element to lose half its radioactivity through natural atomic change

Example

The half-life of uranium-238 is about 4.5 billion years, making it useful for dating ancient rocks.

half-life of [isotope] + is + duration

Students in the lab measured the half-life of a small sample of radioactive cobalt over three weeks.

Common collocations
  • radioactive half-life
  • physical half-life
  • half-life of uranium
  • half-life measured in years
  • have a half-life of
Synonyms
  • decay period

    a less common, more technical term used in physics textbooks

  • half-value period

    an older or more formal term for the same concept, rarely used in everyday speech

Grammar Patterns

the half-life of [substance]

[substance] + has/ have + a half-life of [duration]

Usage Note

Can be followed by 'of' to specify which substance (e.g. 'the half-life of carbon-14'). Frequently used as a countable noun, though the singular form is far more common.

Common Mistakes

The half-life time of uranium is long.
The half-life of uranium is long.
'half-life' already includes the idea of time; adding 'time' is redundant.
Half-life of this element is 10 years.
The half-life of this element is 10 years.
always use the definite article when specifying a substance.

2. the time a living body needs to process a chemical substance until its level in

2.nounB2
Definition

the time a living body needs to process a chemical substance until its level in the blood reaches fifty percent of the starting amount

Example

The drug's half-life in the blood is about six hours, so patients take it twice a day.

drug's half-life determines dosing schedule

Caffeine has a half-life of roughly five hours in most adults, though the exact time varies from person to person.

Common collocations
  • biological half-life
  • elimination half-life
  • plasma half-life
  • drug half-life
  • have a half-life of
  • short half-life
  • long half-life
Synonyms

Grammar Patterns

the half-life of [drug/substance]

[substance] + has/ have + a half-life of [duration]

[possessive] + half-life

Usage Note

Commonly used with a possessive noun ('the drug's half-life') or with 'of' ('the half-life of the medication'). The context is almost always medical or pharmaceutical.

Common Mistakes

This medicine's half-life period is 12 hours.
This medicine's half-life is 12 hours.
'period' is unnecessary; half-life already implies a period of time.

3. a way of describing how quickly a feeling, popular idea, or memory loses about h

3.nounC1
Definition

a way of describing how quickly a feeling, popular idea, or memory loses about half of its original strength and begins to fade away

Example

The public outrage over the scandal had a surprisingly short half-life and faded within a week.

figurative: half-life of an emotional reaction

Online trends now have such a brief half-life that a viral video can be forgotten in just a few days.

Common collocations
  • short half-life
  • brief half-life
  • long half-life
  • cultural half-life
  • emotional half-life
  • have a half-life of
Synonyms
  • shelf life

    more common for physical products but also used figuratively; implies usefulness before something expires rather than fading gradually

  • fade rate

    less common; used informally to describe how fast something loses its impact

Grammar Patterns

a + [adjective] + half-life

the half-life of [feeling/trend/idea]

Usage Note

A figurative extension of the scientific term. Often modified by adjectives ('short half-life', 'long half-life') and found in informal journalism, opinion writing, or casual conversation about cultural phenomena.

Common Mistakes

The half-life of this fashion trend is 3 months.
This fashion trend has a half-life of about 3 months.
the 'have a half-life of' structure is more natural than 'the half-life of X is Y' in figurative use.

Word family

  • half-lives
    noun (plural)B2

Synonym discussion

Sense: noun/1

While all three terms relate to radioactive substances, they differ in what they measure. Half-life is the most common term and refers to a specific duration: the time needed for half of the atoms to decay. Decay period is a broader, less precise term that can refer to any length of time involved in the decay process, not just the half-life point. Disintegration rate describes the speed at which atoms break down, usually expressed as decays per second rather than as a length of time. For everyday science communication, half-life is the clearest choice: 'Uranium-238 has a half-life of 4.5 billion years' is more natural than 'Uranium-238 has a decay period of…' or 'a disintegration rate of…'.

half-life ↗decay perioddisintegration rate

Common collocations

Nouns

  • half-life measurement
  • half-life calculation
  • half-life value

Phrases

  • have a half-life of
  • with a half-life of
  • the half-life of

Prepositions

Etymology

GermanEnglish

Half-life was first used in English around 1907 by the physicist Ernest Rutherford. He combined 'half' (meaning one of two equal parts) with 'life' (meaning duration of existence) to describe the time it takes for half of a radioactive substance to decay. The model was based on an earlier German term 'Halbwertzeit' (half-value time). Over time the term was adopted by medicine and then by general language as a metaphor for anything that fades away at a steady rate.