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Radioactive decay calculator

Calculate activity and specific activity from radioactive isotope mass, molar mass and half-life, or solve for one missing quantity.

Activity (Bq)
417,422,988,872,912,540,000.000
Specific activity (Bq/kg)
417,422,988,872,912,500,000,000.000
Radioisotope mass
1
Isotope molar mass (g/mol)
100.000000
Half-life
10
Parent atoms
6,022,140,760,000,000,000,000.000
Activity (Ci)
11,281,702,401.970610

Estimates for information only. Not financial, medical, legal or engineering advice. See the Terms.

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How this calculator works

Convert the mass of one parent radioisotope to atoms using its isotope molar mass and the exact Avogadro constant. Multiply by decay constant to obtain disintegrations per second. Specific activity here is per kilogram of that isotope, not per kilogram of a diluted bulk sample. Daughter activity and decay-chain equilibrium are excluded.

Formula

A = lambda N = [ln(2)/T] [m(g)/M(g/mol)] N_A. 1 Bq = 1 disintegration/s; 1 Ci = 3.7 x 10^10 Bq.

Worked example

One mole of parent atoms with T = ln(2) seconds has activity 6.02214076 x 10^23 Bq. Half a mole under the same condition has half that activity.

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Frequently asked questions

Can I use a natural element molar mass?

Use the molar mass of the actual isotope, especially for an enriched sample.

Does this calculate radiation dose?

No. Activity alone does not determine absorbed or effective dose.

Can I model the activity later?

Apply the half-life calculator to this initial activity for a single parent isotope.

Sources

Written byAmira MansourCalculator writer. Builds and tests Mathulate calculators against published sources.
Reviewed byMarc LefebvreMathematics teacher. Checks each formula and worked example by hand.

Last updated .

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