Decay calculations
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NNDC/ENSDF provides decay data; source activity comes from a certificate, order line, inventory record or manual input.
The calculator computes radionuclide activity at any date using the radioactive decay law A = A₀·e^(−λt), where the decay constant λ = ln2 / T½. Select an isotope, enter the certificate activity and set the calibration and use dates.
Three modes are available: activity at a date, required initial activity (how much to order with a margin for decay by delivery) and time to a target activity. Half-life comes from the NNDC/ENSDF dataset (ENDF/B-VIII.0, 3561 nuclides) or is entered manually.
Calculations are deterministic; the data source and version are stored with every saved calculation. The model covers single-nuclide decay and does not solve decay chains.
Pick the nuclide, enter the certificate activity and calibration date, then the target date. The calculator applies the decay law A = A₀·e^(−λt) with the ENDF/B-VIII.0 half-life and shows the activity, the remaining fraction and the number of half-lives elapsed.
From the ENDF/B-VIII.0 library (NNDC), 3561 nuclides. For commercial nuclides such as Co-60, Cs-137, Ir-192 and Am-241 the values agree with DDEP recommended data within 0.25 %. For regulatory paperwork always check the source certificate.
No: the calculator follows the decay of a single nuclide. For Cs-137, Ra-226 and other chains the daughters in equilibrium are handled by the dose-rate calculator and the nuclide card; here the result refers to the parent nuclide only.