millicuries

The millicurie (mCi) is a unit of radioactivity used to quantify the rate at which a radioactive substance decays. It represents one thousandth of a curie, a non-SI unit historically common in radiology, radiopharmacology, and nuclear medicine.

In terms of si units, 1 curie equals 3.7 × 10^10 disintegrations per second (Bq). Therefore, 1 millicurie equals 3.7 × 10^7 disintegrations per second, or 37 megabecquerels (MBq). For reference, 1 microcurie is 3.7 × 10^4 Bq (about 37 kilobecquerels). The becquerel is the SI unit of activity, and while it is now the standard in many fields, the curie and its subunits like the millicurie are still encountered, especially in radiopharmaceuticals and certain regulatory contexts in the United States.

The millicurie is commonly used to express the activity of radiopharmaceutical doses, calibration standards, and some laboratory assays. Because radioactive decay changes activity over time according to the radionuclide’s half-life, calculations involving decay, remaining activity, and dose rates are routinely performed when issuing and administering mCi-valued quantities.

Etymology and context: the curie is named after Marie and Pierre Curie and was defined in the early 20th century. The millicurie is simply a decimal subdivision of the curie, serving practical needs in medicine and research. In modern practice, many professionals convert values to becquerels (1 mCi = 37 MBq) for consistency with the SI system.