Radioactive Decay Calculator

Radioactive Decay Calculator

The Radioactive Decay Calculator computes radioactive activity in Becquerels (Bq) and specific activity in Bq/g from sample mass, molar mass, and half-life. Activity measures how many nuclear disintegrations occur per second.

The activity formula is:

$$A = N_A \cdot \frac{m}{M_a} \cdot \frac{\ln 2}{t_{1/2}}$$

where $N_A$ is Avogadro's number ($6.022 \times 10^{23}$ mol$^{-1}$), $m$ is sample mass in grams, $M_a$ is molar mass in g/mol, and $t_{1/2}$ is half-life in seconds.

Specific activity (activity per gram) is:

$$a = \frac{N_A}{M_a} \cdot \frac{\ln 2}{t_{1/2}}$$

For a banana with about 0.5 g potassium containing $^{40}$K (half-life $1.248 \times 10^9$ years, molar mass 39.96 g/mol), activity is roughly 16 Bq. A 6.19 kg plutonium-239 core yields activity on the order of terabecquerels.

Related tools: Half-Life Calculator and Molar Mass Calculator.