The "Specific Activity" is the number of decays per unit time of a radioactive sample. The SI unit of radioactive activity is the becquerel (Bq), in honor of the scientist Henri Becquerel.
$a = \frac{A}{m}$, where $A$ is the activity of a sample and $m$ is its mass.
Applicable units are those of quantitykind:SpecificActivity
Specific Activity