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Half-Life Calculator

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Calculate remaining quantity after radioactive or exponential decay from half-life and elapsed time, plus decay constant and mean lifetime.

Initial quantity (N₀)

Half-life (t½)

Elapsed time (same unit as half-life)

Time unit (label only)

N(t) = N₀ × (1/2)^{t / t½}. Common half-lives: Carbon-14 ≈ 5,730 years, Iodine-131 ≈ 8.02 days, Caesium-137 ≈ 30.1 years.

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update v1.0

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Enter the initial quantity, the half-life and the elapsed time in the same unit. Results update as you type.

Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.