The unit of radioactivity named after the Curies is the curie, abbreviated Ci. It measures radioactive activity by counting the number of nuclear decays occurring each second in a sample.
One curie was originally defined as the activity of one gram of radium-226, reflecting the Curies' pioneering investigations of radium. In modern terms, one curie equals 3.7 × 10¹⁰ becquerels, or 37 billion nuclear transformations per second.
The name honours Marie Curie and Pierre Curie, although historical accounts note that the naming decision did not always clearly specify whether the unit commemorated one scientist or both. The curie is still encountered in older scientific and medical contexts, while the becquerel is the official SI unit of radioactivity.