The unit of measurement for radioactivity is the Becquerel (Bq). One Becquerel is defined as one disintegration or nuclear decay event per second, indicating the activity of a radioactive source. This unit is essential in fields such as nuclear physics, health physics, and radiology, as it helps quantify the amount of radioactive materials and their potential effects on human health and the environment. Understanding radioactivity measurement is critical for safety and regulatory protocols.