Radioactive Activity Calculator

What is Radioactive Activity?

Radioactive activity (A) is the rate at which atoms in a radioactive sample disintegrate, measured in becquerels (Bq) where 1 Bq equals one disintegration per second. The older unit curie (Ci) equals 3.7 × 10¹θ Bq, originally defined as the activity of one gram of radium-226.

The Activity Formula

Activity is calculated using the formula: A = λN

Where:

A = Activity in becquerels (Bq)
λ = Decay constant in inverse seconds (s&supmin;¹)
N = Number of radioactive atoms

How to Use the Calculator

Select the variable you want to solve for:

Solve for Activity (A): Enter decay constant and number of atoms to calculate activity
Solve for Decay Constant (λ): Enter activity and number of atoms
Solve for Number of Atoms (N): Enter activity and decay constant

Activity can be displayed in becquerels (Bq, kBq, MBq, GBq) or curies (Ci, mCi, μCi) with automatic conversion.

Applications

Radioactive activity calculations are used in:

Nuclear medicine for radiopharmaceutical dosing
Radiation safety and exposure monitoring
Environmental monitoring of contamination levels
Industrial radiography source calibration
Smoke detector design and testing

Also check: Exponential Decay Calculator, Half-Life Calculator, STP Calculator, Density Calculator, Specific Heat Calculator, and Unit Converter.

Frequently Asked Questions

How do you calculate radioactive activity?

Multiply the decay constant by the number of radioactive atoms: A = λN. The result is in becquerels when λ is in s&supmin;¹.

What units is activity measured in?

The SI unit is the becquerel (Bq), one decay per second. The older curie (Ci) equals 3.7 × 10¹θ Bq and is still used in medical and nuclear industry contexts.

How is activity different from radiation dose?

Activity counts disintegrations per second, while dose measures energy absorbed per unit mass (gray, Gy) and biological harm (sievert, Sv). A high-activity source far away may deliver less dose than a lower-activity source held in your hand.

Does activity stay constant over time?

No — activity decreases exponentially at the same rate as the number of atoms, since A = λN and N decays exponentially. A freshly produced medical isotope is far more active than the same sample after a few half-lives.

Report