Radioactivity calculator (activity to mass)

This calculator estimates the mass of a single radionuclide corresponding to a known activity, using evaluated nuclear data.

It supports tasks such as interpreting activity measurements, estimating inventories, reviewing historical records, and converting activity-based limits or results into a mass-equivalent value for planning and communication.

If you know the mass of a radionuclide and need to estimate the resulting activity, use the Radioactivity calculator (mass to activity).

What the calculator on this page does

For a selected radionuclide, the calculator uses the radionuclide’s specific activity to convert activity into mass:

  • You select the radionuclide (element and mass number; isomer where relevant).

  • You enter the activity value (with selectable activity units).

  • The calculator outputs the corresponding mass in your chosen mass unit.

For transparency, the calculator also displays the specific activity value used for the selected radionuclide. This provides a direct sense-check and helps validate that the correct radionuclide has been selected.

Supported units

Activity units

The calculator supports:

  • becquerels (Bq), kilobecquerels (kBq), megabecquerels (MBq), gigabecquerels (GBq), terabecquerels (TBq)

  • picocuries (pCi), nanocuries (nCi), microcuries (µCi), millicuries (mCi), curies (Ci)

Mass units

Mass may be output in:

  • nanograms (ng), micrograms (µg), milligrams (mg), grams (g), kilograms (kg), metric tonnes (t)

Note: the tonne unit used is the metric tonne (t) = 1,000 kg, consistent with UK practice.

Data sources and assumptions

This calculator is based on established nuclear data:

  • Half-life data: ICRP Publication 107

  • Atomic mass data: AME2020 (Atomic Mass Evaluation 2020)

Specific activity is derived from these values and is displayed to the user.

Appropriate use and limitations

  • This calculator is intended for single-radionuclide calculations.
    If your material contains a mixture of radionuclides, additional calculations are required to interpret results correctly.

  • The calculator does not account for:

    • decay chains and ingrowth (unless explicitly addressed in your input assumptions);

    • measurement uncertainty or sampling bias;

    • matrix effects or chemical form.

Outputs should be interpreted in context and should not replace professional judgement or formal characterisation methods where these are required.

For advice on radioactive substances within your organisation or regulatory framework, please contact RP Alba Ltd.