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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.
Trinn-for-trinn guide
- 1Remaining quantity: N(t) = N₀ × (1/2)^(t/t½)
- 2N₀ = initial amount, t = elapsed time, t½ = half-life
- 3Equivalently: N(t) = N₀ × e^(−λt) where λ = ln(2)/t½
- 4After 10 half-lives: only ~0.1% of the original remains
Løste eksempler
Inndata
Carbon-14 (t½=5,730yr), 1,000 atoms, 11,460 years
Resultat
250 atoms remaining
2 half-lives: 1000→500→250
Inndata
Drug half-life 8 hours, dose 500mg, after 24 hours
Resultat
62.5 mg remaining
3 half-lives: 500→250→125→62.5