Curie (unit)

The curie (Ci) is a non-SI unit of radioactivity, originally defined in 1910. It is defined as the activity of a quantity of radioactive material that decays at the same rate as 1 gram of radium-226.

Currently, one curie is defined as 3.7 × 10¹⁰ disintegrations per second (dps), or 37 gigabecquerels (GBq). Thus:

1 Ci = 3.7 × 10¹⁰ Bq = 37 GBq 1 Bq = 2.703 × 10^-11 Ci

The curie is named after Marie Curie, a pioneer in radioactivity research. While still sometimes used, the becquerel (Bq), an SI-derived unit, is the preferred unit for measuring radioactivity. The curie is now mostly used in the United States.