Half-Life Calculator
Work out how much of a radioactive substance remains after a time, how long decay takes, or the half-life itself.
Amount remaining
25
- Percent remaining
- 25%
- Half-lives elapsed
- 2
- Decay constant (λ)
- 0.000120968 per year
- Mean lifetime (τ)
- 8,266.64 years
Show the work
Half-lives that have passed
t ÷ t½
11,460 ÷ 5,730 = 2
Halve the amount that many times
N = N₀ × 0.5 to the power of t ÷ t½
100 × 0.5 to the power of 2 = 25
How it works
N = N₀ × (½)^(t ÷ T½); decay constant λ = ln 2 ÷ T½; mean lifetime τ = T½ ÷ ln 2
Questions
- How does the half-life calculator work?
- N = N₀ × (½)^(t ÷ T½); decay constant λ = ln 2 ÷ T½; mean lifetime τ = T½ ÷ ln 2.
- What do I need to enter?
- Solve for, Time unit, Starting amount (N₀), Amount remaining (N), Time elapsed, Half-life (T½). Optional fields can be left blank.
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