Curie (unit)

Short description: Non-SI unit of radioactivity

Curie

A sample of radium, the element which was used in the original definition of the curie.

General information
Unit of| Activity
Symbol| Ci
Named after| Pierre Curie and Marie Curie
Conversions
1 Ci in ...| ... is equal to ...
rutherfords|  37000 Rd
SI derived unit|  37 GBq
SI base unit|  3.7×1010 s−1
Sample of cobalt-60 that emits 1 μCi (microcurie) of radioactivity; i.e. 37,000 decays per second.

The curie (symbol Ci) is a non-SI unit of radioactivity originally defined in 1910. According to a notice in Nature at the time, it was to be named in honour of Pierre Curie,[1] but was considered at least by some to be in honour of Marie Skłodowska–Curie as well,[2] and is in later literature considered to be named for both.[3]

It was originally defined as "the quantity or mass of radium emanation in equilibrium with one gram of radium (element)",[1] but is currently defined as 1 Ci = 3.7×1010 decays per second[4] after more accurate measurements of the activity of 226Ra (which has a specific activity of 3.66×1010 Bq/g[5]).

In 1975 the General Conference on Weights and Measures gave the becquerel (Bq), defined as one nuclear decay per second, official status as the SI unit of activity.[6] Therefore:

1 Ci = 3.7×1010 Bq = 37 GBq

and

1 Bq ≅ 2.703×10−11 Ci ≅ 27 pCi

While its continued use is discouraged by the National Institute of Standards and Technology (NIST)[7] and other bodies, the curie is still widely used throughout government, industry and medicine in the United States and in other countries.

At the 1910 meeting, which originally defined the curie, it was proposed to make it equivalent to 10 nanograms of radium (a practical amount). But Marie Skłodowska–Curie, after initially accepting this, changed her mind and insisted on one gram of radium. According to Bertram Boltwood, Marie Skłodowska–Curie thought that "the use of the name 'curie' for so infinitesimally small [a] quantity of anything was altogether inappropriate".[2]

The power emitted in radioactive decay corresponding to one curie can be calculated by multiplying the decay energy by approximately 5.93 mW / MeV.

A radiotherapy machine may have roughly 1000 Ci of a radioisotope such as caesium-137 or cobalt-60. This quantity of radioactivity can produce serious health effects with only a few minutes of close-range, unshielded exposure.

Radioactive decay can lead to the emission of particulate radiation or electromagnetic radiation. Ingesting even small quantities of some particulate emitting radionuclides may be fatal. For example, the median lethal dose (LD-50) for ingested polonium-210 is 240 μCi; about 53.5 nanograms. However, millicurie quantities of electromagnetic emitting radionuclides are routinely used in nuclear medicine.

The typical human body contains roughly 0.1 μCi (14 mg) of naturally occurring potassium-40. A human body containing 16 kg (35 lb) of carbon (see Composition of the human body) would also have about 24 nanograms or 0.1 μCi of carbon-14. Together, these would result in a total of approximately 0.2 μCi or 7400 decays per second inside the person's body (mostly from beta decay but some from gamma decay).

## Contents

* 1 As a measure of quantity
* 2 Radiation related quantities
* 3 See also
* 4 References

## As a measure of quantity

Units of activity (the curie and the becquerel) also refer to a quantity of radioactive atoms. Because the probability of decay is a fixed physical quantity, for a known number of atoms of a particular radionuclide, a predictable number will decay in a given time. The number of decays that will occur in one second in one gram of atoms of a particular radionuclide is known as the specific activity of that radionuclide.

The activity of a sample decreases with time because of decay.

The rules of radioactive decay may be used to convert activity to an actual number of atoms. They state that 1 Ci of radioactive atoms would follow the expression

N (atoms) × λ (s−1) = 1 Ci = 3.7 × 1010 Bq,

and so

N = 3.7 × 1010 Bq / λ,

where λ is the decay constant in s−1.

Here are some examples, ordered by half-life:

Isotope | Half-life | Mass of 1 curie | Specific activity (Ci/g)

|
|
|

209Bi | 1.9×1019 years | 11.1 billion tonnes | 9.01×10−17
232Th | 1.405×1010 years | 9.1 tonnes | 1.1×10−7 (110,000 pCi/g, 0.11 μCi/g)
238U | 4.471×109 years | 2.977 tonnes | 3.4×10−7 (340,000 pCi/g, 0.34 μCi/g)
40K | 1.25×109 years | 140 kg | 7.1×10−6 (7,100,000 pCi/g, 7.1 μCi/g)
235U | 7.038×108 years | 463 kg | 2.2×10−6 (2,160,000 pCi/g, 2.2 μCi/g)
129I | 15.7×106 years | 5.66 kg | 0.00018
99Tc | 211×103 years | 58 g | 0.017
239Pu | 24.11×103 years | 16 g | 0.063
240Pu | 6563 years | 4.4 g | 0.23
14C | 5730 years | 0.22 g | 4.5
226Ra | 1601 years | 1.01 g | 0.99
241Am | 432.6 years | 0.29 g | 3.43
238Pu | 88 years | 59 mg | 17
137Cs | 30.17 years | 12 mg | 83
90Sr | 28.8 years | 7.2 mg | 139
241Pu | 14 years | 9.4 mg | 106
3H | 12.32 years | 104 μg | 9,621
228Ra | 5.75 years | 3.67 mg | 273
60Co | 1925 days | 883 μg | 1,132
210Po | 138 days | 223 μg | 4,484
131I | 8.02 days | 8 μg | 125,000
123I | 13 hours | 518 ng | 1,930,000
212Pb | 10.64 hours | 719 ng | 1,390,000
223Fr | 22 minutes | 26 ng | 38,000,000
212Po | 299 nanoseconds | 5.61 ag | 1.78×1017

## Radiation related quantities

The following table shows radiation quantities in SI and non-SI units:

Ionising radiation related quantities view ‧ talk ‧ edit Quantity | Unit | Symbol | Derivation | Year | SI equivalence

|
|
|
|
|

Activity (A)  | becquerel | Bq  | s−1 | 1974  | SI unit
curie | Ci  | 3.7 × 1010 s−1 | 1953  | 3.7×1010 Bq
rutherford | Rd  | 106 s−1 | 1946  | 1,000,000 Bq
Exposure (X)  | coulomb per kilogram | C/kg  | C⋅kg−1 of air  | 1974  | SI unit
röntgen | R  | esu / 0.001293 g of air  | 1928  | 2.58 × 10−4 C/kg
Absorbed dose (D)  | gray | Gy  | J⋅kg−1 | 1974  | SI unit
erg per gram  | erg/g  | erg⋅g−1 | 1950  | 1.0 × 10−4 Gy
rad | rad  | 100 erg⋅g−1 | 1953  | 0.010 Gy
Dose equivalent (H)  | sievert | Sv  | J⋅kg−1 × WR | 1977  | SI unit
röntgen equivalent man | rem  | 100 erg⋅g−1 | 1971  | 0.010 Sv

## See also

* Geiger counter
* Ionizing radiation
* Radiation burn
* Radiation exposure
* Radiation poisoning
* United Nations Scientific Committee on the Effects of Atomic Radiation

## References

1. ↑ 1.0 1.1 Rutherford, Ernest (6 October 1910). "Radium Standards and Nomenclature". Nature 84 (2136): 430–431. doi:10.1038/084430a0. Bibcode: 1910Natur..84..430R. https://archive.org/stream/nature841910lock/nature841910lock_djvu.txt.
2. ↑ 2.0 2.1 Frame, Paul (1996). "How the Curie Came to Be". Health Physics Society Newsletter. http://www.orau.org/ptp/articlesstories/thecurie.htm. Retrieved 3 July 2015.
3. ↑ United States Atomic Energy Commission (1951). Semiannual Report of the Atomic Energy Commission, Volume 9. p. 93. https://books.google.com/books?id=7fUrAAAAIAAJ&pg=RA5-PA93.
4. ↑ "Resolution 7 of the 12th CGPM". International Bureau of Weights and Measures (BIPM). 1964. https://www.bipm.org/en/CGPM/db/12/7/.
5. ↑ Delacroix, D. (2002). "Radionuclide and Radiation Protection Data Handbook 2002". Radiation Protection Dosimetry (Nuclear Technology Publishing) 98 (1): 147. doi:10.1093/oxfordjournals.rpd.a006705. PMID 11916063. http://rpd.oxfordjournals.org/content/98/1/1.
6. ↑ "SI units for ionizing radiation: becquerel". Resolutions of the 15th CGPM (Resolution 8). 1975. http://www.bipm.org/en/CGPM/db/15/8/. Retrieved 3 July 2015.
7. ↑ ﻿NIST Special Publication 811, paragraph 5.2﻿ (Report). NIST. 28 January 2016. https://www.nist.gov/pml/pubs/sp811/sec05.cfm#52. Retrieved 22 March 2016.

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Scientists whose names are used as units

SI base units|

* André-Marie Ampère (ampere)
* William Thomson, 1st Baron Kelvin (kelvin)

SI derived units|

* Henri Becquerel (becquerel)
* Anders Celsius (degree Celsius)
* Charles-Augustin de Coulomb (coulomb)
* Michael Faraday (farad)
* Louis Harold Gray (gray)
* Joseph Henry (henry)
* Heinrich Hertz (hertz)
* James Prescott Joule (joule)
* Isaac Newton (newton)
* Georg Ohm (ohm)
* Blaise Pascal (pascal)
* Werner von Siemens (siemens)
* Rolf Maximilian Sievert (sievert)
* Nikola Tesla (tesla)
* Alessandro Volta (volt)
* James Watt (watt)
* Wilhelm Eduard Weber (weber)

Non-SI metric (cgs) units|

* Anders Jonas Ångström (angstrom)
* Peter Debye (debye)
* Loránd Eötvös (eotvos)
* Galileo Galilei (gal)
* Johann Carl Friedrich Gauss (gauss)
* William Gilbert (gilbert)
* Heinrich Kayser (kayser)
* Johann Heinrich Lambert (lambert)
* Samuel Pierpont Langley (langley)
* James Clerk Maxwell (maxwell)
* Hans Christian Ørsted (oersted)
* Jean Léonard Marie Poiseuille (poise)
* Sir George Stokes, 1st Baronet (stokes)
* John William Strutt, 3rd Baron Rayleigh (rayl)

Imperial and US customary units|

* Daniel Gabriel Fahrenheit (degree Fahrenheit)
* Johann Heinrich Lambert (foot-lambert)
* William John Macquorn Rankine (degree Rankine)

Non-systematic units|

* Alexander Graham Bell (bel)
* Marie Curie (curie)
* Pierre Curie (curie)
* John Dalton (dalton)
* Michael Faraday (faraday)
* Heinrich Mache (Mache)
* John Napier (neper)
* René Antoine Ferchault de Réaumur (degree Réaumur)
* Wilhelm Röntgen (roentgen)
* J. J. Thomson (thomson)
* Evangelista Torricelli (torr)

List of scientists whose names are used as units · Scientists whose names are used in physical constants · People whose names are used in chemical element names

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