Example 1
If 100 units fall to 25 units in 20 years, the half-life is 10 years.
Mendeleev
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Physics tools › Half-life calculator
Mendeleev · Physics
Half-life calculator
If you know how much of a radioactive population remains after a measured time, you can infer its half-life from the exponential decay law.
Formula usedT½ = t·ln2 / ln(N₀/N)
Visual cue · nuclei remaining
Calculate
Half-life calculator
Calculated resultHalf-life
What do the symbols mean?
T½half-life
N₀initial amount
Nremaining amount
Δtelapsed time
Two worked examples
Example 2
If half the initial amount remains after 5 hours, the half-life is 5 hours.
Good to knowThis calculation requires 0 < N < N₀ and a positive elapsed time.