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What is a half-life?

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Quick answer

A half-life is the time it takes for half of a radioactive substance to decay. After one half-life, half remains; after two, a quarter; and so on. Each element has its own fixed half-life, which scientists use for dating and in medicine.

Key things to understand

  1. It's the time for half a substance to decay.
  2. Each radioactive element has a fixed half-life.
  3. After each half-life, half of what's left decays.
  4. It's used in carbon dating and nuclear medicine.

People also ask

What is a half-life?
The time it takes for half of a radioactive sample to decay into something else.
How does half-life work over time?
Each half-life halves what remains: 100% → 50% → 25% → 12.5%, and so on.
What is half-life used for?
Radiometric dating of ancient objects, nuclear power, and timing doses in medicine.