Polonium
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Polonium (symbol: Po) is a chemical element, one of the chalcogens. It is a silvery-white metal with a unique simple cubic structure,[1] although it is rare that polonium or its compounds are encountered in weighable quantities.
Polonium has no stable isotopes, and the metal and all its compounds are intensely radioactive. The power output due to the radioactive decay of polonium-210 is about 140 W g−1, which leads to considerable self-heating and which complicates the investigation of its properties with macroscopic quantities.[1]
Contents
History
Polonium was discovered in 1898 by Marie Curie while she was investigating the radioactivity of pitchblende. The isolation of miligram quantities of polonium required the processing of over 15 tonnes of ore, and earned Marie Curie the Nobel Prize for Chemistry in 1911. The element was named after Curie's native Poland.[1]
Occurrence and production
The only naturally ocurring isotope of polonium is polonium-210 (t½ = 138.38 days), the penultimate member of the radium decay series. It occurs in uranium ores at about 0.1 mg per tonne of ore (a mass fraction of about 10−10). The overall abundance of polonium in crustal rocks can be estimated at about 3 × 10−10 ppm.[1]
Extraction of polonium from natural sources is impractical, and it is produced commercially by the neutron irradiation of bismuth in a nuclear reactor: 20983Bi(n,γ)21083Bi. The bismuth-210 produced undergoes β-decay (t½ = 5.01 days) to give polonium-210.[1] Commercial production is about 85 grams per year, 97% of which is produced by a single facility near Samara in Russia.[3]
Use
Polonium-210 is a vitually pure α-emittor (Eα = 5.30 MeV), with only 0.0011% γ-decay, and is used as an intense source of α-particles.[1]
The main commercial use is in anti-static brushes, which can contain up to 500 µCi (20 MBq) 210Po. The α particles ionize molecules from the air, which allows an equalization of charges on the surface being brushed and the helps the mechanical removal of dust particles. Smaller quantities – typically 4–40 kBq (0.1–1.0 µCi) – are occasionally used as α particle sources for teaching and research. In both cases, these are sealed sources.
Polonium-210 is also used in a mixture with beryllium oxide as a portable source of neutrons through the 94Be(α,n)126C reaction. The self-heating of polonium-210 has also been used as a source of heat and/or thermoelectric power in space exploration.[1]
Notes and references
Notes
- ↑ Atomic weight of polonium-210, which is by far the most commonly encountered isotope.
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; pp 882–919. ISBN 0-08-022057-6.
- ↑ CRC Handbook of Chemistry and Physics, 62nd ed.; Weast, Robert C., Ed.; CRC Press: Boca Raton, FL, 1981; p E-65. ISBN 0-8493-0462-8.
- ↑ Most Polonium Made Near the Volga River. St. Petersburg Times 2007-01-23, <http://www.sptimesrussia.com/index.php?action_id=2&story_id=20100>.
Further reading
- Polonium; Moyer, Harvey V., Ed.; United States Atomic Energy Commission: Oak Ridge, Tenn., 1956. TID-5221. doi:10.2172/4367751, <http://www.osti.gov/bridge/servlets/purl/4367751-nEJIbm/>.
External links
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