Curie
Definition and meaning of Curie in chemistry.
The curie (Ci) is an older unit used to measure radioactivity. It shows how fast a sample of radioactive atoms breaks down over time. One curie equals exactly 3.7 × 10^10 atomic decays every second.
In more detail
This unit is named after the famous scientists Marie and Pierre Curie. They did pioneering early research on radioactive elements in their laboratory. The unit was first based on the decay rate of one gram of radium-226.
In 1975, scientists introduced the becquerel as the official standard unit. One becquerel represents just one decay per second, which is a very tiny amount. Since one curie is a very large unit, it can be dangerous to work with directly.
A common student misconception is that the curie measures the amount of radiation that hits a person. In reality, it only measures how active the radioactive source itself is. Today, the curie is still widely used in the United States.
Doctors use this unit in nuclear medicine to plan treatment doses. Engineers also use it to monitor waste at nuclear power plants. Since medical doses are quite small, doctors usually measure them in millicuries.
Each millicurie is one thousandth of a curie. Scientists also use microcuries, which are one millionth of a curie.
Key facts
| Symbol | Ci |
|---|---|
| SI equivalent | 1 Ci = 3.7 × 10^10 Bq |
| Named after | Marie and Pierre Curie |
| Field | Physical Chemistry |
| Common sub-units | Millicurie (mCi), microcurie (uCi) |
| Measurement type | Radioactivity decay rate |
A doctor needs to test a patient's thyroid gland using radioactive iodine-131. The patient receives a liquid capsule containing a dose of eight millicuries. This dose is equal to exactly eight thousandths of a single curie. In the official metric system, this activity equals about 2.96 × 10^8 becquerels. The dose is strong enough to show the thyroid on a scan but safe enough for the patient. After the test, the radioactive iodine decays quickly in the body. This scan helps the doctor find tumors or other thyroid problems.
Frequently asked questions
What is the SI equivalent of the curie?
One curie equals exactly 3.7 × 10^10 becquerels in the modern system. The becquerel is the official SI unit for measuring radioactive decays.
Is the curie still an official unit?
No, the becquerel has been the official metric unit of radioactivity since 1975. However, the curie is still common in American medicine and industry.
Does a curie measure radiation exposure?
No, this unit only measures how many atoms decay each second in a sample. Other units measure the actual radiation energy absorbed by the body.