(Ci) a curie corresponds to the radioactivity emitted by a gram of pure Radium-226, one of the first natural radioactive materials available and isolated at the beginning of the last century. In principle this unit should no longer be used because it was replaced by the becquerel (see entry for this word) in the 1980s. However, as habits are difficult to change and as Ci, and particularly millicuries (mCi) are more convenient to use, this unit was preferably used in this document