The radioactivity of a substance can be measured by finding the rate at which atoms decay in a given period of time. The basic unit of measurement of radioactivity is the curie (Ci), which equals 37 billion disintegrations per second. One thousandth of a curie is a millicurie and one millionth is a microcurie; these units are used to calculate the dosage of radioactivity administered for therapeutic procedures in much the same way that units such as the gram and milligram are used to measure dosages of medications. The curie may eventually be replaced by a new SI unit of radioactivity, the becquerel (Bq), which is equal to 1 disintegration per second. One microcurie equals 37 kilobecquerels.