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Specific Radioactivity Calculator (Bq/mol, Ci/mmol, Ci/g)

· Last updated：2026-08-22

Carrier-free specific activity from the half-life: A = ln2·N_A/T½ in Bq/mol and Ci/mmol, with optional Bq/g and Ci/g from molar mass.

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Tool usage guide

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Key facts

Category
Math & Numbers
Input types
number, select
Output type
json
Sample coverage
4
API ready
Yes

Overview

The Specific Radioactivity Calculator computes the theoretical carrier-free molar and mass specific activity of any radionuclide from its physical half-life and optional molar mass. Using standard decay constants and Avogadro's number, it delivers immediate conversions across Bq/mol, Ci/mmol, Bq/g, and Ci/g to establish theoretical maximum activity thresholds for radiochemistry and radiopharmaceutical labeling.

When to use

  • Determining the theoretical carrier-free specific activity ceiling for radiotracers and labelled biomolecules.
  • Converting radioisotope half-lives into molar activity units (Bq/mol and Ci/mmol) for assay design.
  • Evaluating mass-based specific activity limits (Bq/g and Ci/g) when compound molar mass is known.

How it works

  1. 1Enter the physical half-life value and select the corresponding time unit (seconds, minutes, hours, days, or years).
  2. 2Optionally enter the radionuclide or labeled compound molar mass in grams per mole (g/mol) and choose output decimal precision.
  3. 3The tool applies the decay constant equation (A = ln(2) × N_A / T½) to calculate molar activity, then derives mass specific activity if molar mass is provided.
  4. 4Review calculated outputs displayed in standard radioactivity units including Bq/mol, Ci/mmol, Bq/g, and Ci/g.

Use cases

  • Radiopharmaceutical quality control: Setting baseline ceilings for peptide or antibody labeling efficiency.
  • Nuclear medicine research: Determining theoretical specific activities for diagnostic isotopes like Tc-99m, Ga-68, or F-18.
  • In vitro binding assays: Estimating maximum molar activity for tritiated (³H) or iodinated (¹²⁵I) radioligands.

Examples

1. Carrier-Free Activity of Technetium-99m

Radiochemist

Background

A radiochemist is formulating a Tc-99m labeled peptide and needs to know the theoretical carrier-free limit per gram.

Problem

Calculate the theoretical upper bound for molar and mass activity of Tc-99m to benchmark batch purity.

How to use

Enter half-life 6.01, select hours as the unit, set molar mass to 99, and set decimal places to 2.

halfLife: 6.01, halfLifeUnit: hours, molarMass: 99, decimalPlaces: 2

Outcome

Yields 1.93×10¹⁹ Bq/mol (521,431.64 Ci/mmol) and 1.95×10¹⁷ Bq/g (5,266,990 Ci/g).

2. Molar Activity Limit for Tritium (³H)

Assay Developer

Background

An assay developer is designing a receptor binding screen using tritiated ligands.

Problem

Determine the theoretical maximum molar activity of carrier-free ³H over its 12.32-year half-life.

How to use

Enter half-life 12.32, select years as the unit, leave molar mass blank, and set decimal places to 2.

FAQ

What does carrier-free specific activity mean?

Carrier-free specific activity represents the theoretical maximum radioactivity per mole or gram when 100% of the atoms in the sample are the radioactive isotope, containing no stable carrier isotopes.

Why are experimental specific activities lower than calculated values?

Real-world preparations contain stable carrier atoms, chemical impurities, or decay daughters, which increase mass and molar quantity relative to the radioactive decays.

Is entering the molar mass required?

No, molar mass is optional. If omitted, the calculator outputs molar activities (Bq/mol and Ci/mmol); providing molar mass enables mass-specific outputs (Bq/g and Ci/g).

Which time units are supported for half-life?

You can input half-life values in seconds, minutes, hours, days, or years.

How are Curie (Ci) and Becquerel (Bq) related in the calculation?

Calculations convert Becquerels to Curies using the standard physical constant 1 Ci = 3.7 × 10¹⁰ Bq.

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halfLife: 12.32, halfLifeUnit: years, decimalPlaces: 2

Outcome

Yields 1.074×10¹⁵ Bq/mol, corresponding to 29.02 Ci/mmol.