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

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.

> Canonical page: https://elysiatools.com/en/tools/specific-radioactivity

- **Category:** Math & Numbers

- **Keywords:** specific radioactivity, specific activity, molar activity, carrier free, ci/mmol, bq/mol, avogadro, radionuclide, radiochemistry, radiolabeling

## 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.

## Inputs

- **Half-life T½** (number): Physical half-life in the selected time unit. Must be greater than zero.
- **Half-life T½** (select): Time unit of the half-life.
- **Molar Mass (g/mol, optional)** (number): Molar mass of the radionuclide or labelled compound in g/mol; if provided, mass-based specific activity (Bq/g, Ci/g) is computed.
- **Decimal Places** (number)

## 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

- Enter the physical half-life value and select the corresponding time unit (seconds, minutes, hours, days, or years).
- Optionally enter the radionuclide or labeled compound molar mass in grams per mole (g/mol) and choose output decimal precision.
- The 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.
- Review 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.

## Frequently asked questions

### 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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