Radioactive half-life
Radioactive half-life: use initial quantity, elapsed time, half-life in the same time units. Review the formula, worked example and calculation steps.
Inputs
Use the units shown—
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Formula & explanation
Remaining quantity = initial × 2^(−elapsed/half-life)
Variables & units
- Initial quantity
- Numeric value · minimum 0, maximum 1000000000000
- Elapsed time
- time units · minimum 0, maximum 1000000000
- Half-life in the same time units
- time units · minimum 0.000001, maximum 1000000000
Worked example
100 units after 20 time units with a half-life of 10 leaves 25.
Assumptions
Single exponential decay without new production or daughter-product accumulation. Use consistent time units.
Formula version 1.0.0. JavaScript floating-point arithmetic applies. Results display up to 6 decimal places; stored values retain available precision. Use the units shown.
Practice with an example
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