curie

n. (Abbr. Ci)
A unit of radioactivity, equal to the amount of a radioactive isotope that decays at the rate of 3.7 × 10¹⁰ disintegrations per second.

[After Pierre CURIE.]

The former unit of activity (see radiation units). It is named after Marie Curie.

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(kyōō′rē)

A measurement of radioactivity produced by the disintegration of unstable elements. The curie is that quantity of a radioactive nuclide in which the number of disintegrations per second is 3.700 times 10^-10. Since the curie is a relatively large unit, the millicurie (0.00 curie) and the microcurie (one-millionth of a curie) are more often used. The curie is based on the number of nuclear disintegrations and not on the number or amount of radiations emitted.

[Etymology: P. Curie; France 1859-1906] radiation physics. Symbol Ci. The most widely known but now obsolescent unit of radioactivity, originally defined as the amount of radioactivity deriving from 1 gram of radium, but divorced from that element and generalized in 1953 to be the quantity of any radionuclide that had 3.7 × 10¹⁰ disintegrations per second (the rounded number of the original definition).
[Curtiss L. F., Evans R. D., Johnson W., Seaborg G. T. Rev. Sci. Instrum. Vol. 21, 94 (1950)] The name was originally accepted at the 1910 International Congress of Radiology and Electricity in Brussels,
[Rutherford E. Nature Vol. 84, 430-1 (1910)] its matching standard developed under the control of Mme. Sklodowska Curie. Succeeded in 1975 by the becquerel, 1 curie = 37 GBq, but the 1978 decision of the CIPM considering it acceptable to continue to use the curie with the SI still stands.

The curie, as agreed in 1910, was defined technically as the radioactivity of the amount of radon gas in equilibrium with 1 gram of radium.
[Glasser O. Physical Foundations of Radiology, 2nd edn (New York: Harper, 1952)] Such radiation is mixed in type, so the number of disintegrations is not the number of particles produced, nor does the generalized definition imply the number of particles produced; see becquerel for further discussion.

Although not coherent with the metric system in any way, the curie was widely subject to the metric prefixes. In particular, because of the curie being a large unit for very many uses, millicurie (mCi) and microcurie (μCi) were common expressions. The more rounded and appropriately sized rutherford of 10⁶ disintegrations per second was accepted in 1949, but has rarely been used.

The curie was not applicable to X-rays and other electromagnetic radiations, the roentgen being the parallel unit for those, but one subsequently overlapping the curie by being applied generally to ionization. Nor was the curie a measure of absorbed dose, i.e. of the amount of energy imparted to matter by the indicated radiation; this was the rem.

For intensity millicurie see sievert.

1964	12th CGPM: ‘accepts that the curie be still retained, outside SI, as the unit of activity, with the value 3.7 × 1010s-1. The symbol for this unit is Ci.’see note below

[Le Système International d'Unités (Sèvres, France: Bureau International de Poids et Mesures, 1985)]

A non-SI unit of radioactivity, defined as the quantity of any radioactive nuclide in which the number of disintegrations per second is 3.7 × 10¹⁰; abbreviated Ci. Now replaced by the becquerel.

IN BRIEF: n. - A unit of radioactivity equal to the amount of a radioactive isotope that decays at the rate of 37,000,000,000 disintegrations per second.

Tutor's tip: A "cure" is a remedy for an ailment, a "cure" is a parish priest, while a "curie" is a unit of radiation.

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