plutonium

plutonium

a highly toxic metallic transuranic element. It occurs in trace amounts in uranium ores and is produced in a nuclear reactor by neutron bombardment of uranium-238. The most stable and important isotope, plutonium-239, readily undergoes fission and is used as a reactor fuel in nuclear power stations and in nuclear weapons. Symbol: Pu; atomic no.: 94; half-life of ²³⁹Pu: 24 360 years; valency: 3, 4, 5, or 6; relative density (alpha modification): 19.84; melting pt.: 640°C; boiling pt.: 3230°C

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

plutonium

[plü′tō·nē·əm]

(chemistry)

A reactive metallic element, symbol Pu, atomic number 94, in the transuranium series of elements; the first isotope to be identified was plutonium-239; used as a nuclear fuel, to produce radioactive isotopes for research, and as the fissile agent in nuclear weapons.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

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 It might be outdated or ideologically biased.

Plutonium

 

Pu, an artificial radioactive chemical element with atomic number 94; an element of the actinide series.

Plutonium was discovered in 1940–41 by the American scientists G. Seaborg, E. McMillan, J. Kennedy, and A. Wahl, who obtained the isotope ²³⁸ Pu as a result of irradiation of uranium by nuclei of heavy hydrogen (deuterons). The new element was named for the planet Pluto, as the precursors of plutonium in the Mendeleev table, uranium and neptunium, were named for the planets Uranus and Neptune.

Isotopes of plutonium with mass numbers from 232 to 246 are known. Traces of the isotopes ²⁴⁷ Pu and ²⁵⁵ Pu were discovered in dust collected after explosions of thermonuclear bombs. The longest-lived isotope of plutonium is the α-radioactive ²⁴⁴ Pu, which has a half-life of about 7.5 × 10⁷ yr. The half-lives of all the isotopes of plutonium are much less than the age of the earth, and therefore all the primary plutonium that existed on the planet at the time of its formation has completely decayed. However, extremely small amounts of ²³⁹ Pu are continuously formed during -β–decay of ²³⁹ Np, which in turn is formed in the nuclear reaction of uranium with neutrons, such as the neutrons of cosmic rays. Thus, traces of plutonium are found in uranium ores.

Plutonium is a shiny white metal that exists in six allotropic modifications at temperatures from room temperature to 640°C (its melting point). The allotropie transitions of plutonium are accompanied by discontinuous changes in its density (see Figure 1). A unique feature of metallic plutonium is that it contracts upon heating from 310° to 480°C, rather than expanding, as do other metals.

Figure 1. Change in density of metallic plutonium upon heating

The configuration of the three outer electron shells of the plutonium atom is 5s²5p⁶5d¹⁰5f⁶6s²6p²7s². The chemical properties of plutonium are very similar to those of its precursors in the periodic system, uranium and neptunium. Plutonium forms compounds with oxidation states from + 2 to +7. The oxides PuO, Pu₂O₃, and PuO₂ and a phase of mixed composition, Pu₂O₃—Pu₄O₇, are known. In its compounds with halogens, plutonium usually has an oxidation state of +3, although the halides PuF₄, PuF₆, and PuCl₄ are also known. In solutions, plutonium exists in the forms Pu³⁺, Pu⁴⁺, PuO2 + (plutonoyl ion), PuO 2²⁺ (plutonyl ion), and PuO₅^3–, which correspond to oxidation states from + 3 to +7. These ions, with the exception of PuO₅^3–, may be in solution simultaneously in equilibrium. Ions of plutonium of all oxidation states have a tendency toward hydrolysis and complexing.

Of all the isotopes of plutonium, the most important is the α-radioactive ²³⁹ Pu, with a half-life of 2.4 × 10⁴ yr. The nuclei of ²³⁹ Pu are capable of fission by chain reaction under the action of neutrons, and therefore ²³⁹ Pu may be used as a source of atomic energy (the energy released by the disintegration of 1 g of ²³⁹ Pu is equivalent to the heat released upon combustion of 4,000 kg of coal).

In the USSR, the first attempts to produce ²³⁹ Pu began in 1943–44 under the direction of Academicians I. V. Kurchatov and V. G. Khlopin. Plutonium was first isolated in the USSR in 1945 from a sample of uranium under neutron bombardment. In a very short time, extensive studies of the properties of plutonium were carried out, and in 1949 the first plant for the radiochemical separation of plutonium began operation in the USSR.

The industrial production of ²³⁹ Pu is based on the reaction of nuclei of ²³⁸U with neutrons in nuclear reactors. The subsequent separation of plutonium from uranium, neptunium, and highly radioactive fission products is carried out by radiochemical methods, such as coprecipitation, extraction, and ion exchange. Metallic plutonium is usually produced by reduction of PuF₃, PuF₄, or PuO₂ by vapors of barium, calcium, or lithium. The isotope ²³⁹Pu is used as a fissionable material in atomic reactors and in atomic and thermonuclear bombs. The isotope ²³⁸Pu is used for the production of atomic batteries with a service life of 5 yr or more. Such batteries may be used, for example, in current generators for cardiac pacemakers.

REFERENCES

Bagley, K. Plutonii i ego splavy. Moscow, 1958. (Translated from English.)
Vdovenko, V. M., and B. V. Kurchatov. “Pervyi sovetskii plutonii.” Radiokhimiia, 1968, vol. 10, fasc. 6, p. 696.
Plutonii: Spravochnik, vols. 1–2. Edited by O. Wick. Moscow, 1971–73. (Translated from English.)
See also references under ACTINIDES.

S. S. BERDONOSOV

Plutonium in the organism. Plutonium is concentrated by marine organisms. Its coefficient of accumulation, which is the ratio of the concentration in the organisms to that in the environment, is 1,000–9,000 for algae, about 2,300 for plankton (mixed), up to 380 for mollusks, about 1,000 for starfish, and 5, 570, 200, and 1,060 for the muscles, bones, liver, and stomach tissue of fishes, respectively. Terrestrial plants take up plutonium mainly through their root system and accumulate it up to 0.01 percent of their weight.
In the human body, plutonium is retained primarily in the skeleton and liver, from which it is virtually not eliminated (particularly in the case of the skeleton). The most toxic isotope is ²³⁹Pu, which disrupts hematopoiesis and causes osteosarcomas and lung cancer. In the 1970’s, the fraction of plutonium in the radioactive pollution of the biosphere has been increasing: the intensity of irradiation of marine invertebrates by plutonium has become greater than that by ⁹⁰Sr and ¹³⁷Cs.

REFERENCES

Problemy toksikologii plutoniia. Moscow, 1969.
Radioaktivnye veshchestva i kozha (Metabolizm i dezaktivatsiia). Moscow, 1972.
Uranium, Plutonium, Transplutonic Elements. Berlin-Heidelberg-New York, 1973.

G. G. POLIKARPOV

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