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polonium (pəlōˈnēəm), radioactive chemical element; symbol Po; at. no. 84; mass no. of most stable isotope 209; m.p. 254℃; b.p. 962℃; sp. gr. about 9.4; valence +2 or +4. Polonium is an extremely rare element found in uranium ores (about 0.1 gram per ton). A product of radium decay, it is sometimes called radium F. In its physical and chemical properties it resembles tellurium (the element above it in Group 16 of the periodic table) and bismuth.

Polonium has 34 isotopes, more than any other element. All of these isotopes are radioactive. The most stable, polonium-209, has a half-life of about 103 years. Polonium-208 (half-life about 3 years) is the only other polonium isotope with a half-life over one year. Although these two isotopes can be prepared in small quantities in a particle accelerator, they are very expensive to produce.

All other polonium isotopes are short-lived except polonium-210 (half-life about 138 days), which is the most commonly used isotope. It is prepared by bombarding bismuth with neutrons in a nuclear reactor. It is a highly radioactive material. A milligram of polonium-210 emits as much alpha radiation as about 5 grams of radium, and enough gamma radiation to cause a blue glow in the air around it. It can be used as a heat source, since most of the energy of the alpha radiation is absorbed as heat within the polonium and its container.

Polonium has found use in small portable radiation sources and in the control of static electricity. However, it is an extremely toxic substance and must be handled with great care. Polonium was the first element to be discovered because of its radioactivity; it was discovered in pitchblende in 1898 by Marie Curie and named for her native country, Poland.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



Po, a radioactive chemical element of Group VI in the Mendeleev periodic table. Atomic number, 84. Polonium was the first element to be discovered by P. Curie and M. Sklo-dowska-Curie because of its radioactive properties (1898); it was named for Poland (Latin Polonid), Mme. Curie’s native land.

There are 25 known radioactive polonium isotopes, with mass numbers ranging from 194 to 218. The longest-lived isotope is the artificially produced α-radioactive 209Po (half-life T½ = 103 yr). Seven polonium isotopes with mass numbers 210–212, 214–216, and 218 occur naturally as members of the radioactive series of uranium, actinouranium, and thorium; α-radioactive 210Po (T½ = 138days) is the most stable of the latter isotopes. Milligram quantities of 210Po may be extracted from natural substances, and also synthesized artificially by the nuclear interaction of neutrons and bismuth. Virtually all data on polonium have been obtained using 210Po.

Polonium is a rare element; the Po content in the earth’s crust is approximately 2 × 10-15 percent. Polonium occurs in free form as a soft, silver-white metal: density, 9.3 g/cm3; melting point, 254°C; boiling point, 1162°C. The configuration of the outer electron shell in the Po atom is 6s2 6p4. Polonium is most similar to tellurium in chemical properties. Like tellurium, polonium has the oxidation states –2, +2, +4, and +6. The known polonium oxides are PoO, PoO2, and PoO3. The volatile hydride P0H2 is formed upon action of Zn on a hydrochloric acid solution of Po; the ions PoO42-, PoO32-, Po4+, and PoO2+ are present in Po solutions. The polonium hydroxide Po(OH)2 is known.

Readily hydrolyzable polonium tetrahalides and sulfates of various compositions are synthesized in weighable quantities. The carrier method, using tellurium, an analogue of polonium, is used in the synthesis of organopolonium compounds, in which Po carbon bonding occurs. For example, polonium diphenyl (C6H5)2Po and polonium diphenyldichloride (C6H5PoCl2 have been obtained. Since polonium is extremely toxic, all work with this element is carried out in special boxes.

The isotope 210Po is used in neutron sources. Energy from the α-particles of 210Po may be transformed into electric power. In particular, small electric “atomic” batteries made with 210Po, which are characterized by a long service life, were used in the satellites Cosmos 84 and Cosmos 89.


Bagnall, K. Khimiia redkikh radioaktivnykh elementov: Polonii-aktinii. Moscow, 1960. (Translated from English.)
Bagnall, K. Khimiia selena, tellura i poloniia. Moscow, 1971.
Ershova, Z. V., and A. G. Volgin. Polonii i ego primenenie. Moscow, 1974.


Polonium-210 (2l0Po). The isotope 210Po is a common constituent of natural radioactive fallout. It passes into plants from the soil through the roots or from the atmosphere through precipitation onto epigeal plant organs. Small quantities of 210Po (10–4 picocurie per g [pc/g]) are found in seawater; the isotope may accumulate in marine organisms (the accumulation coefficient in the algae Porphyra umbilicalis is of the order of 1,000).

Animals and humans ingest 210Po with food. For example, the approximate 210Po content in salt water fish is 20–100 pc/kg; in meat, 2–3 pc/kg; in bread, 1 pc/kg; in groats, 2 pc/kg; and in tea, 500–600 pc/kg. Polonium is relatively evenly distributed among the organs in animals and humans (specific concentration ~4 × 10-5pc/g in raw tissue).

The biological effect of 210Po is determined by α-radiation. Animal experiments have indicated the high toxicity of this radionuclide in large concentrations. For example, 210Po concentrations higher than 0.0003 μc/g liveweight reduced the life span of white rats, altered peripheral blood composition, and induced cirrhosis of the liver; the animals later developed tumors in the kidneys, large intestine, testes, and many other organs. The biological effect of small 210Po concentrations has not been thoroughly studied.


Raspredelenie i biologicheskoe deistvie radioaktivnykh isotopov: Sb. st. Moscow, 1966.
Metody radioekologicheskikh issledovanii: Sb. st. Moscow, 1971.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


A chemical element, symbol Po, atomic number 84; all polonium isotopes are radioactive; polonium-210 is the naturally occurring isotope found in pitchblende.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


a very rare radioactive element that occurs in trace amounts in uranium ores. The isotope polonium-210 is produced artificially and is used as a lightweight power source in satellites and to eliminate static electricity in certain industries. Symbol: Po; atomic no.: 84; half-life of most stable isotope, 209Po: 103 years; valency: --2, 0, 2, 4, or 6; relative density (alpha modification): 9.32; melting pt.: 254°C; boiling pt.: 962°C
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005