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Radioactive decay and half-life

How much of a sample remains after a given time, given its half-life.

Showing a worked example. Change the values and the result updates, and the answer lives in the URL.

Decay

Half-lives elapsed1
Remaining50N = N₀ × (1/2)^(t/t½)
Decayed50
Fraction remaining50%
Decay constant λ0.0001209681λ = ln2 / t½
Mean lifetime τ8,266.64258429τ = 1 / λ, longer than the half-life
Time to 1% remaining38,069.295967

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Radioactive decay and half-life | Nerdulator