Curie (unit)

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The curie (symbol Ci) is a non-SI unit of radioactivity, originally defined in 1910. According to an advisory in "Nature& #3. 4; at the time, it was named in honor of Marie Curie.

It was originally defined as "the magnitude or mass of radium emanation in equilibrium with one gram of radium (element), but is normally defined as 1 Ci = 3.7 x 10^{10< /sup> decays per second after more precise measurements of the ²²⁶Ra activity (which has a specific activity of 3.66 x 10¹⁰ Bq / g).}

In 1975, the "General Conference on Weights and Measures" it gave the becquerel (Bq), defined as one nuclear decay per second, official status as the SI unit for activity. Thus:

1 Ci = 3.7 x 10¹⁰ Bq = 37 MBq

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)" and other bodies, the curie is still widely used throughout government, industry, and medicine in the United States and 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 Curie, after initially accepting that, changed her mind and insisted on one gram of radium. According to Bertram Boltwood, Marie Curie thought that "the use of the name "curie" for an infinitesimally small magnitude of anything it was totally inappropriate".

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

A radiation therapy machine should have as little as 1000 Ci of a radioisotope such as cesium-137 or cobalt-60. This magnitude of radioactivity can produce serious health effects with just a few minutes of unshielded exposure at close range.

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

Typically, the human body contains just 0.1 μCi (14 mg) of naturally occurring potassium-40. A human body containing 15 kg of carbon (see Composition of the human body), too, may have about 24 nanograms or 0.1 μCi of carbon-14. Together, these could result in a total of about 0.2 μCi or 7400 decays per second inside the person's body (mostly as beta decay, but some as gamma decay).

As a measure of magnitude

The units of activity (the curie and the becquerel) also refer to the magnitudes of atoms of radioactivity. Since the probability of decay is a fixed physical quantity, for a known number of atoms of a particular radionuclide, a predictable number will decay at any 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 due to decay.

The radioactive decay rules must be used to convert activity to actual number of atoms. The state that 1 Ci of atoms of radioactivity will follow the expression:

${displaystyle No, no.$

and so on

${displaystyle N=(3.7times 10^{10}){frac {text{Bq}}{lambda }}}}}{displaystyle N=$
Symbol	Name	Unit
${displaystyle N}$	atoms
${displaystyle lambda }$	constant disintegration	s^-1

Also, we can express activity in moles:

${cHFFFFFF}{cH00FF00}{cH00FF00}{cH00FF00}{cH00FF00}{cH00FF00}{cH00FFFF00}{cH00FFFF00}{cH00FF00}{cH00FF00}{cH00FFFF00}{cH00FFFFFFFF00}{cH00}{cH00}{cH00}{cH00}{cH00FFFFFFFFFFFFFFFF00}{cH00}{cH00}{cH00}{cH00FFFFFFFFFFFFFFFFFF00FFFFFFFFFFFFFFFFFFFFFFFF00}{cH00}{cH00}{cH00}{cH00}{cH00}{cH00FF00FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF$


Symbol	Name
${displaystyle N_{A}}$	Number of Avogradro
${displaystyle t_{1/2}$	Average life

The number of moles must be converted to grams by multiplying by the atomic mass.

Here are some examples, ordered by half-life.


Isotopo	Average life	Mass of 1 curie	Specific activity (Ci/g)
²⁰⁹Bi	1.9×10¹⁹years	11.1 billion tons	9.01×10⁻¹⁷
²³²Th	1.405×10¹⁰years	9.1 tons	1.1×10⁻⁷(110,000 pCi/g, 0.11 μCi/g)
²³⁸U	4.471×10⁹years	2,977 tons	3.4×10⁻⁷(340,000 pCi/g, 0.34 μCi/g)
⁴⁰K	1.25×10⁹years	140 kg	7.1×10⁻⁶(7.100,000 pCi/g, 7.1 μCi/g)
²³⁵U	7.038×10⁸years	463 kg	2.2×10⁻⁶(2.160,000 pCi/g, 2.2 μCi/g)
¹²⁹I	15.7×10⁶years	5.66 kg	0.00018
⁹⁹Tc	211×10³years	58 g	0.017
²³⁹Pu	24.11×10³years	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
⁹⁰Mr.	28.8 years	7.2 mg	139
²⁴¹Pu	14 years	9.4 mg	106
³H	12.32 years	104 μg	9621
²²⁸Ra	5.75 years	3.67 mg	273
⁶⁰Co	1925 years	883 μg	1132
²¹⁰Po	138 years	223 μg	4484
¹³¹I	8.02 years	8 μg	125000
¹²³I	1 p.m.	518 ng	1930000
²¹²Pb	10.64 a.m.	719 ng	1390 000
²²³Fr	22 minutes	26 ng	38000
²¹²Po	299 nanoseconds	5.61 ag	1.78×10¹⁷

Related quantities of radiation


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

Curium represented a very large amount of radioactivity from a biological point of view, so smaller units began to be used:

milicurie (mCi) = 10^-3 Ci
microcury (μCi) = 10^-6 Ci
nanocury (nCi) = 10^-9 Ci
(pCi) = 10^-12 Ci

The curie has been replaced by a derived SI unit, the becquerel (Bq):

1 Bq = 2,703 × 10^-11Ci

1 Ci = 3.7 × 10¹⁰Bq

Radiation dose

The curium indicates how alpha or beta particles or gamma rays were emitted from a radioactive source, per unit time, but it does not indicate how such radiation might affect living organisms.

Radiation dose is measured in grais.

Data: Q229354

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