A Curie (Ci) is a standard measurement for radioactivity, specifically the rate of Decay for a gram of radium - 37 billion decays per second. A unit of radioactivity equal to 3.7 x 10 ¹⁰ disintegrations per second.

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A curie (Ci) is a unit quantity of any radioactive nuclide in which there are 37 billion atomic transformations (disintegrations) in one second. A measure of radioactivity based on the observed decay rate of approximately one gram of radium. The Curie was named in honor of Pierre and Marie Curie, pioneers in the study of radiation.