The curie (symbol Ci) is a unit of radioactivity, defined as

1 Ci = 3.7×10¹⁰ decays per second or becquerels.

This is roughly the activity of 1 gramme of the radium isotope ²²⁶Ra, a substance studied by the pioneers of radiology, Marie and Pierre Curie. The curie has since been replaced by an SI derived unit, the becquerel (Bq), which equates to one decay per second. Therefore:

1 Ci = 3.7×10¹⁰ Bq

and

1 Bq = 2.70×10⁻¹¹ Ci

The unit is named after Pierre and/or Marie Curie^[1][2]