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Half Life Calculator

Half-Life Calculator

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Detailed Guide Coming Soon

We're working on a comprehensive educational guide for the Half Life Calculator in your language. The content below is shown in English.

Qu'est-ce que Half Life Calculator?

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Half-life is the time required for half of a substance to undergo decay or be eliminated. It applies to radioactive decay, drug metabolism, and chemical reactions. After n half-lives, the remaining fraction is (1/2)ⁿ.

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Comment Half Life Calculator

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  1. 1Remaining quantity: N(t) = N₀ × (1/2)^(t/t½)
  2. 2N₀ = initial amount, t = elapsed time, t½ = half-life
  3. 3Equivalently: N(t) = N₀ × e^(−λt) where λ = ln(2)/t½
  4. 4After 10 half-lives: only ~0.1% of the original remains

Exemples résolus

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Exemple 1
Donné:Carbon-14 (t½=5,730yr), 1,000 atoms, 11,460 years
Résultat:250 atoms remaining

2 half-lives: 1000→500→250

Exemple 2
Donné:Drug half-life 8 hours, dose 500mg, after 24 hours
Résultat:62.5 mg remaining

3 half-lives: 500→250→125→62.5

Notable Half-Lives

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SubstanceHalf-lifeApplication
Carbon-145,730 yearsArchaeological dating
Uranium-2384.47 billion yearsGeological dating
Iodine-1318.02 daysMedical imaging / therapy
Caffeine (in body)5–6 hoursDrug metabolism
Alcohol~1 drink/hourBAC reduction
Aspirin15–20 minutesDrug metabolism
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Conseil Pro

In medicine, it takes about 4–5 half-lives for a drug to reach steady state in the body, and 4–5 half-lives to be substantially eliminated. This guides dosing frequency.

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Le saviez-vous?

Radiocarbon dating (carbon-14) can only date materials up to ~50,000 years old — about 9 half-lives. Beyond that, too little C-14 remains to measure accurately. For older materials, potassium-40 (half-life 1.25 billion years) is used.

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Reviewed October 2026
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