basic

Radioactive Decay Activity from Half-Life and Number of Atoms Calculator

A = λN = (ln 2 / t½) · N.

Compute the activity A of a radioactive sample: A = λN = (ln 2 / t½) · N, where t½ is the half-life in seconds and N is the number of radioactive atoms. Also reports N from mass and molar mass so you can go directly from grams of isotope to activity in Becquerels.

Dr. Helena Ortiz By Dr. Helena Ortiz
Published Last reviewed 1 min read

Inputs

g
g/mol
s

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

A = (ln2 / t½) · N; N = (m / M) · Nₐ.

In depth

Compute the activity A of a radioactive sample: A = λN = (ln 2 / t½) · N, where t½ is the half-life in seconds and N is the number of radioactive atoms. Also reports N from mass and molar mass so you can go directly from grams of isotope to activity in Becquerels.