A former non-SI unit of radioactivity named after Marie Curie. It was originally defined as the volume of radon gas in equilibrium with 1 g of radium-226. It is now associated with the quantity of a radioactive isotope that decays at a rate of 3.7×1010 disintegrations per second. The becquerel (symbol Bq) is the SI-derived unit of radioactivity where one Bq is equal to one disintegration per second. The millicurie (mCi) and microcurie (μCi) are also used.