What is meant by the term 'activity' in the context of radioactivity?

In the context of radioactivity, the term 'activity' specifically refers to the rate at which radioactive decay occurs in a sample. This is quantitatively expressed as the number of decays per unit of time, usually measured in units like becquerels (Bq) or curies (Ci). This rate indicates how many radioactive atoms are transforming or decaying into other elements or isotopes over that time period.

Understanding activity is crucial for radiation safety because it helps assess the potential exposure individuals may have to radiation and informs the necessary safety measures. It is distinct from other concepts such as energy released, which pertains to the energy emitted during decay, or mass, which relates to the amount of material present. The lifespan of radioactive elements, while related to their decay processes, does not define the immediate rate of activity.