Specific Activity Calculator

Mode	Key Inputs	Output Summary
Measured	5 MBq, 250 mg, 96% purity, 85% isotope fraction, 92% efficiency, 3 h elapsed, 6 h half-life	Corrected specific activity ≈ 37.676 MBq/g
Theoretical	8 day half-life, 131 g/mol molar mass, 100% abundance, 50 mg sample	Theoretical specific activity ≈ 4.610004E+15 Bq/g

Formula Used

Measured specific activity

Corrected activity = (Measured activity ÷ detector efficiency) × decay correction

Decay correction = 2^{(elapsed time ÷ half-life)}

Effective isotope mass = total sample mass × purity fraction × isotope fraction

Specific activity = corrected activity ÷ effective isotope mass

Theoretical specific activity

Specific activity = (ln2 × N_A ÷ half-life ÷ molar mass) × isotopic abundance fraction

Where ln2 is the natural log of 2 and N_A is Avogadro’s constant.

How to Use This Calculator

Select either the measured or theoretical calculation mode.
Enter activity, mass, purity, efficiency, and decay details for measured work.
Enter half-life, molar mass, and abundance for theoretical work.
Choose your preferred output unit such as Bq/g or MBq/g.
Press the calculate button to display the result above the form.
Review the graph, interpretation block, and supporting conversion values.
Export the result using the CSV or PDF buttons.

FAQs

1. What does specific activity mean?

Specific activity is the radioactivity per unit mass of a substance. It commonly appears as Bq/g, MBq/g, or Ci/g in radiochemistry and isotope work.

2. Why does purity affect the result?

Impurities increase total mass without contributing useful radioactivity. That lowers the activity per gram of active material and reduces the calculated specific activity.

3. Why is detector efficiency included?

Measured activity can be lower than true activity when instrument efficiency is below 100%. Efficiency correction helps estimate the actual activity before mass normalization.

4. When should I apply decay correction?

Use decay correction when measurement occurs after a reference time, such as labeling, purification, or calibration. It adjusts the activity back to the chosen reference point.

5. What is the difference between measured and theoretical mode?

Measured mode uses experimental inputs like activity, mass, efficiency, and purity. Theoretical mode estimates the maximum possible specific activity from nuclear properties alone.

6. Which output unit should I choose?

Choose a unit that matches your workflow. MBq/g is common in laboratory reporting, while Ci/g or mCi/g may suit older regulatory or reference documents.

7. Why compare to theoretical specific activity?

Comparing against the theoretical maximum shows how close a preparation is to ideal radiochemical performance. It can reveal dilution, contamination, or incomplete enrichment.

8. Can this calculator replace lab validation?

No. It is useful for estimation, screening, and education. Final release, quality control, and regulated reporting should always follow validated laboratory methods.