Calculator
Radioactive decay
Remaining activity of a sealed source between its loading date and the calculation date, from the isotope half-life.
Activity on the calculation dateCi
- In TBq
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- Days elapsed
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- Remaining activity
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Method
A(t) = A₀ × 2^(−t / T½)
- A₀ — activity at loading in Ci
- t — days between the two dates
- T½ — isotope half-life in days
The calculation uses reference half-lives (73.827 / 119.79 / 1925.28 days), not rounded values. It ignores reloads, source ageing and certificate uncertainties.
Indicative result — check it against your authorisation and your dosimetry.