Radioactivity

The property of an unstable atomic nucleus losing energy by emitting radiation (radioactive decay). Radioactivity also refers to the expectation value of the number of radioactive decays occurring in a given quantity of material per unit time. The SI unit of radioactivity is per second (s-1) and its special name is becquerel (Bq). Also called activity.

ICRP Glossary entry - June 2019