Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025
Definition
Activity is the measure of the number of radioactive decays per unit time in a given sample. It is typically measured in becquerels (Bq) or curies (Ci).
The SI unit for activity is the becquerel (Bq), which corresponds to one decay per second.
Activity decreases over time as a result of radioactive decay, following an exponential decay law.
It can be calculated using the equation $A = \lambda N$, where $A$ is the activity, $\lambda$ is the decay constant, and $N$ is the number of undecayed nuclei.
The relationship between half-life ($T_{1/2}$) and decay constant ($\lambda$) is given by $\lambda = \frac{0.693}{T_{1/2}}$.
Knowing the activity helps in determining the safety and usage of radioactive materials in practical applications.
Review Questions
Related terms
Half-Life: The time required for half of the radioactive nuclei in a sample to undergo decay.