Radioactive Activity Calculator

Calculate radioactive decay activity (Bq, Ci, MBq, GBq) from isotope, sample mass, and half-life.

Inputs

Enter values and click Calculate

Common isotope reference

Isotope Molar mass Half-life Typical use
Ra-226226 g/mol1600 yrHistorical standard, emanation
Cs-137137 g/mol30.17 yrCalibration, industrial gauges
Co-6060 g/mol5.27 yrRadiotherapy, food irradiation
I-131131 g/mol8.02 dThyroid treatment, diagnostics
C-1414 g/mol5730 yrRadiocarbon dating
H-33 g/mol12.32 yrLuminous dials, fusion research
Tc-99m99 g/mol6.02 hMedical imaging (SPECT)

Summary

Calculate radioactive decay activity (Bq, Ci, MBq, GBq) from isotope, sample mass, and half-life.

How it works

  1. Select a preset isotope or enter molar mass and half-life manually.
  2. Choose whether to input sample mass (g) or number of atoms directly.
  3. The decay constant λ = ln(2) / t½ is computed first.
  4. Atom count N = (mass / molar mass) × 6.022×10²³ when mass is given.
  5. Activity A = λ × N, converted to Bq, Ci (÷ 3.7×10¹⁰), MBq, and GBq.

Use cases

  • Estimate activity of a Ra-226 or Cs-137 laboratory source from its mass.
  • Cross-check activity figures for medical isotopes like Tc-99m or I-131.
  • Teach the relationship between half-life, atom count, and decay rate.
  • Convert between Becquerel and Curie units for radiation safety calculations.
  • Verify decay-constant values for nuclear physics coursework.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu