Curie (unit)

non-SI unit of radioactivity

The curie (symbol Ci) is a unit of measurement. It measures radioactivity. It is defined as

1 Ci = 3.7×1010 decays per second.

This is roughly the activity of 1 gram of the radium isotope 226Ra. Radium was studied by the pioneers of radiology, Marie and Pierre Curie so the unit is named after them. The curie has since been replaced by an SI derived unit, the becquerel (Bq), which is decay per second. Therefore:

1 Ci = 3.7×1010 Bq or 37 Gigabecquerel (Gbq)


1 Bq = 2.70×10−11 Ci

In 1962, the International Commission on Radiological Units suggested the usage of this unit named after Marie Curie.