Curie
The curie or Ci is the non-SI unit for radioactive decay measuring the radioactivity of a substance. However, today the official SI unit for radioactive decay is the Becquerel. The curie specifies the amount of ionizing radiation energy that is emitted from an unstable isotope as it decays.[1] Named after Marie Curie, a chemist and the first female to win a Nobel prize after coining the term radioactivity,[2] the Ci also measures the amount of disintegrations per second coming from a decaying element such as Uranium. Originally, the curie was a comparison of the activity of a sample to the activity of one gram of radium, which was measured at 37 billion disintegrations per second.[3] For example, a radioactive sample undergoing 74 billion disintegrations per second has an activity of 2 curies.
The ability to measure the activity of a substance is practical and has many applications. For example, measuring the activity of a substance can help determine the half-life of a sample. One useful application involving half-life is radioactive dating, which is used to determine the age of rocks and other materials, which is how the age of the Earth is known.[4]
The curie is a fairly large unit of measurement, thus it is commonly prefixed to represent a wide range of different activity level, for example:
- Picocuries (pCi): are 1 million millionth of a curie (1 x 10-12 Ci). Picocuries are used in measuring the typically small amount of radioactivity in air and water.
- Megacuries (MCi) are 1 million curies (1 x 106 Ci). Megacuries are used in measuring the very large amount of radioactivity released from nuclear weapons.
The following table shows radiation quantities in SI and non-SI units.[5][6]
| Quantity | Name | Symbol | Unit | System |
|---|---|---|---|---|
| Exposure | Roentgen | R | 2.58x10-6 C/kg | Non-SI |
| Absorbed Dose | Rad Grey |
rad Gy |
10-2 Gy Jkg-1 |
Non-SI SI |
| Activity | Curie Becquerel |
Ci Bq |
3.7x1010 Bq s-1 |
Non-SI SI |
| Dose Equivalent | Roentgen Equivalent Man Sievert |
rem Sv |
10-2 Sv Jkg-1 |
Non-SI SI |
Curie Unit Converter
References
- ↑ U.S.NRC. (06, 21, 2016). Curie (Ci) [Online]. Available: http://www.nrc.gov/reading-rm/basic-ref/glossary/curie-ci.html
- ↑ UNEP. “Radiation Effects and Sources,” United Nations Environment Programme, Austria. Sci. Rep. 978-92-807-3517-8. 2016.
- ↑ E.E. Anderson. “Units of Radiation and Radioactivity.” Public Health Reports, Oak Ridge National Laboratory, Oak Ridge, Tenn. Vol. 67, No. 3, March 1952
- ↑ The TalkOrigins Archive, "The Age of the Earth" [Online], Available: http://www.talkorigins.org/faqs/faq-age-of-earth.html
- ↑ NIST. (2016, February 10). Chapter 5. Guide to the SI, Units Outside the SI [Online]. Available: http://www.nist.gov/pml/pubs/sp811/sec05.cfm
- ↑ NIST. (2016, February 19). Chapter 4. Guide to the SI, The Two Classes of SI Units and the SI Prefixes [Online]. Available: http://www.nist.gov/pml/pubs/sp811/sec04.cfm