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 |
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 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:
and
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 Curie, after initially accepting this, 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 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).
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
and so
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 |
The following table shows radiation quantities in SI and non-SI units:
Quantity | Unit | Symbol | Derivation | Year | SI equivalent |
---|---|---|---|---|---|
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 | |
Equivalent dose (H) | sievert | Sv | J⋅kg−1 × WR | 1977 | SI unit |
röntgen equivalent man | rem | 100 erg⋅g−1 × WR | 1971 | 0.010 Sv | |
Effective dose (E) | sievert | Sv | J⋅kg−1 × WR × WT | 1977 | SI unit |
röntgen equivalent man | rem | 100 erg⋅g−1 × WR × WT | 1971 | 0.010 Sv |
Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources.
Polonium is a chemical element; it has symbol Po and atomic number 84. A rare and highly radioactive metal with no stable isotopes, polonium is a chalcogen and chemically similar to selenium and tellurium, though its metallic character resembles that of its horizontal neighbors in the periodic table: thallium, lead, and bismuth. Due to the short half-life of all its isotopes, its natural occurrence is limited to tiny traces of the fleeting polonium-210 in uranium ores, as it is the penultimate daughter of natural uranium-238. Though longer-lived isotopes exist, such as the 124 years half-life of polonium-209, they are much more difficult to produce. Today, polonium is usually produced in milligram quantities by the neutron irradiation of bismuth. Due to its intense radioactivity, which results in the radiolysis of chemical bonds and radioactive self-heating, its chemistry has mostly been investigated on the trace scale only.
Radium is a chemical element; it has symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rather than oxygen) upon exposure to air, forming a black surface layer of radium nitride (Ra3N2). All isotopes of radium are radioactive, the most stable isotope being radium-226 with a half-life of 1,600 years. When radium decays, it emits ionizing radiation as a by-product, which can excite fluorescent chemicals and cause radioluminescence.
The becquerel is the unit of radioactivity in the International System of Units (SI). One becquerel is defined as an activity of one decay per second. For applications relating to human health this is a small quantity, and SI multiples of the unit are commonly used.
Radioactive decay is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha, beta, and gamma decay. The weak force is the mechanism that is responsible for beta decay, while the other two are governed by the electromagnetism and nuclear force.
In the context of radioactivity, activity or total activity (symbol A) is a physical quantity defined as the number of radioactive transformations per second that occur in a particular radionuclide. The unit of activity is the becquerel (symbol Bq), which is defined equivalent to reciprocal seconds (symbol s-1). The older, non-SI unit of activity is the curie (Ci), which is 3.7×1010 radioactive decay per second. Another unit of activity is the rutherford, which is defined as 1×106 radioactive decay per second.
Radioactive contamination, also called radiological pollution, is the deposition of, or presence of radioactive substances on surfaces or within solids, liquids, or gases, where their presence is unintended or undesirable.
Polonium-210 (210Po, Po-210, historically radium F) is an isotope of polonium. It undergoes alpha decay to stable 206Pb with a half-life of 138.376 days (about 4+1⁄2 months), the longest half-life of all naturally occurring polonium isotopes (210–218Po). First identified in 1898, and also marking the discovery of the element polonium, 210Po is generated in the decay chain of uranium-238 and radium-226. 210Po is a prominent contaminant in the environment, mostly affecting seafood and tobacco. Its extreme toxicity is attributed to intense radioactivity, mostly due to alpha particles, which easily cause radiation damage, including cancer in surrounding tissue. The specific activity of 210
Po is 166 TBq/g, i.e., 1.66 × 1014 Bq/g. At the same time, 210Po is not readily detected by common radiation detectors, because its gamma rays have a very low energy. Therefore, 210
Po can be considered as a quasi-pure alpha emitter.
The measurement of ionizing radiation is sometimes expressed as being a rate of counts per unit time as registered by a radiation monitoring instrument, for which counts per minute (cpm) and counts per second (cps) are commonly used quantities.
Caesium-137, cesium-137 (US), or radiocaesium, is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nuclear weapons. Trace quantities also originate from spontaneous fission of uranium-238. It is among the most problematic of the short-to-medium-lifetime fission products. Caesium-137 has a relatively low boiling point of 671 °C (1,240 °F) and easily becomes volatile when released suddenly at high temperature, as in the case of the Chernobyl nuclear accident and with atomic explosions, and can travel very long distances in the air. After being deposited onto the soil as radioactive fallout, it moves and spreads easily in the environment because of the high water solubility of caesium's most common chemical compounds, which are salts. Caesium-137 was discovered by Glenn T. Seaborg and Margaret Melhase.
The rutherford is a non-SI unit of radioactive decay. It is defined as the activity of a quantity of radioactive material in which one million nuclei decay per second. It is therefore equivalent to one megabecquerel, and one becquerel equals one microrutherford. One rutherford is equivalent to 2.703 × 10−5 curie.
Radium and radon are important contributors to environmental radioactivity. Radon occurs naturally as a result of decay of radioactive elements in soil and it can accumulate in houses built on areas where such decay occurs. Radon is a major cause of cancer; it is estimated to contribute to ~2% of all cancer related deaths in Europe.
Naturally occurring radioactive materials (NORM) and technologically enhanced naturally occurring radioactive materials (TENORM) consist of materials, usually industrial wastes or by-products enriched with radioactive elements found in the environment, such as uranium, thorium and potassium and any of their decay products, such as radium and radon. Produced water discharges and spills are a good example of entering NORMs into the surrounding environment.
In health physics, whole-body counting refers to the measurement of radioactivity within the human body. The technique is primarily applicable to radioactive material that emits gamma rays. Alpha particle decays can also be detected indirectly by their coincident gamma radiation. In certain circumstances, beta emitters can be measured, but with degraded sensitivity. The instrument used is normally referred to as a whole body counter.
Uranium tiles have been used in the ceramics industry for many centuries, as uranium oxide makes an excellent ceramic glaze, and is reasonably abundant. In addition to its medical usage, radium was used in the 1920s and 1930s for making watch, clock and aircraft dials. Because it takes approximately three metric tons of uranium to extract 1 gram of radium, prodigious quantities of uranium were mined to sustain this new industry. The uranium ore itself was considered a waste product and taking advantage of this newly abundant resource, the tile and pottery industry had a relatively inexpensive and abundant source of glazing material. Vibrant colors of orange, yellow, red, green, blue, black, mauve, etc. were produced, and some 25% of all houses and apartments constructed during that period used bathroom or kitchen tiles that had been glazed with uranium. These can now be detected by a Geiger counter that detects the beta radiation emitted by uranium's decay chain.
A gamma ray, also known as gamma radiation (symbol
γ
), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically shorter than those of X-rays. With frequencies above 30 exahertz (3×1019 Hz) and wavelength less than 10 picometer (1×10−11 m) gamma ray photons have the highest photon energy of any form of electromagnetic radiation. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900 while studying radiation emitted by radium. In 1903, Ernest Rutherford named this radiation gamma rays based on their relatively strong penetration of matter; in 1900 he had already named two less penetrating types of decay radiation (discovered by Henri Becquerel) alpha rays and beta rays in ascending order of penetrating power.
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, α. The symbol for the alpha particle is α or α2+. Because they are identical to helium nuclei, they are also sometimes written as He2+
or 4
2He2+
indicating a helium ion with a +2 charge. Once the ion gains electrons from its environment, the alpha particle becomes a normal helium atom 4
2He.
Banana equivalent dose (BED) is an informal unit of measurement of ionizing radiation exposure, intended as a general educational example to compare a dose of radioactivity to the dose one is exposed to by eating one average-sized banana. Bananas contain naturally occurring radioactive isotopes, particularly potassium-40 (40K), one of several naturally occurring isotopes of potassium. One BED is often correlated to 10−7 sievert ; however, in practice, this dose is not cumulative, as the potassium in foods is excreted in urine to maintain homeostasis. The BED is only meant as an educational exercise and is not a formally adopted dose measurement.
A radioactive source is a known quantity of a radionuclide which emits ionizing radiation, typically one or more of the radiation types gamma rays, alpha particles, beta particles, and neutron radiation.
Since its introduction in 1960, the base units for the International system of units, known as SI, have changed several times. Tables in this article summarize those changes.