Curie (unit)
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 1010< /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:
and so on
| Symbol | Name | Unit |
|---|---|---|
| atoms | ||
| constant disintegration | s-1 |
Also, we can express activity in moles:
| Symbol | Name |
|---|---|
| Number of Avogradro | |
| 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 |
| 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 |
| 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 |
| 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.
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Data: Q229354