Curie
Definition and meaning of Curie in chemistry.
The curie (Ci) is a non-SI unit of radioactivity defined as 3.7 × 10^10 disintegrations per second, originally based on the activity of one gram of radium-226.
In more detail
The curie was established in the early 20th century, calibrated to match the decay rate of 1 g of radium-226, and named in honor of Marie and Pierre Curie for their pioneering work on radioactivity. Since 1975, the SI system has used the becquerel (Bq), defined as one disintegration per second, as the standard unit; the curie is now considered non-SI but remains widely used in the United States, particularly in nuclear medicine, radiopharmacy, and reactor engineering. Because it is a large unit, activities are commonly expressed in millicuries (mCi) or microcuries (µCi) for clinical doses.
Key facts
| Symbol | Ci |
|---|---|
| SI equivalent | 1 Ci = 3.7 × 10^10 Bq (disintegrations per second) |
| Named after | Marie and Pierre Curie |
| Field | Physical Chemistry |
A typical diagnostic dose of iodine-131 for a thyroid scan might contain about 5-10 millicuries (mCi) of activity, equivalent to roughly 1.85-3.7 × 10^8 Bq.
Frequently asked questions
What is the SI equivalent of the curie?
1 curie equals 3.7 × 10^10 becquerels, since both units measure disintegrations per second and the becquerel is defined as exactly one disintegration per second.
Is the curie still an official unit?
No. The becquerel has been the official SI unit of radioactivity since 1975, but the curie is still commonly used in the United States, especially in medical and industrial contexts.