Neptunium

Neptunium

History

(Planet Neptune) Neptunium was the first synthetic transuranium element of the actinide series discovered; the isotope 239Np was produced by McMillan and Abelson in 1940 at Berkeley, California, as the result of bombarding uranium with cyclotron-produced neutrons. The isotope 237Np (half-life of 2.14 x 106 years) is currently obtained in gram quantities as a by-product from nuclear reactors in the production of plutonium. Trace quantities of the element are actually found in nature due to transmutation reactions in uranium ores produced by the neutrons which are present. Neptunium is prepared by the reduction of NpF3 with barium or lithium vapor at about 1200C. Neptunium metal has a silvery appearance, is chemically reactive, and exists in at least three structural modifications: alpha-neptunium, orthorhombic, density 20.25 g/cm3, beta-neptunium (above 280C), tetragonal, density (313C) 19.36 g/cm3, gamma-neptunium (above 577C), cubic, density (600C) 18.0 g/cm3. Neptunium has four ionic oxidation states in solution: Np+3 (pale purple), analogous to the rare earth ion Pm+3, Np+4 (yellow green); NpO+ (green blue): and NpO++ (pale pink). These latter oxygenated species are in contrast to the rare earths which exhibit only simple ions of the (II), (III), and (IV) oxidation states in aqueous solution. The element forms triand tetrahalides such as NpF3, NpF4, NpCl4, NpBr3, NpI3, and oxides of the various compositions such as are found in the uranium-oxygen system, including Np3O8 and NpO2. Fifteen isotopes of neptunium are now recognized. The O.R.N.L. has 237Np available for sale to its licensees and for export. This isotope can be used as a component in neutron detection instruments. It is offered at a price of $280/g.

Isotope

Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.

Last Updated: 12/19/97, CST Information Services Team

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Plutonium

Plutonium

For nuclear batteries.

History

(Planet pluto) Plutonium was the second transuranium element of the actinide series to be discovered. The isotope 238Pu was produced in 1940 by Seaborg, McMillan, Kennedy, and Wahl by deuteron bombardment of uranium in the 60-inch cyclotron at Berkeley, California. Plutonium also exists in trace quantities in naturally occurring uranium ores. It is formed in much the same manner as neptunium, by irradiation of natural uranium with the neutrons which are present.

Isotopes

By far of greatest importance is the isotope Pu239, with a half-life of 24,100 years, produced in extensive quantities in nuclear reactors from natural uranium: 238U(n, gamma) --> 239U--(beta) --> 239Np--(beta) --> 239Pu. Fifteen isotopes of plutonium are known.

Plutonium also exhibits four ionic valence states in aqueous solutions: Pu+3 (blue lavender), Pu+4 (yellow brown), PuO+ (pink?), and PuO+2(pink-orange). The ion PuO+ is unstable in aqueous solutions, disproportionating into Pu+4 and PuO+2. The Pu+4 thus formed, however, oxidizes the PuO+ into PuO+2, itself being reduced to Pu+3, giving finally Pu+3 and PuO+2. Plutonium forms binary compounds with oxygen: PuO, PuO2, and intermediate oxides of variable composition;

with the halides: PuF3, PuF4, PuCl3, PuBr3, PuI3; with carbon, nitrogen, and silicon: PuC, PuN, PuSi2. Oxyhalides are also well known: PuOCl, PuOBr, PuOI.

Uses

Plutonium has assumed the position of dominant importance among the trasuranium elements because of its successful use as an explosive ingredient in nuclear weapons and the place which it holds as a key material in the development of industrial use of nuclear power. One kilogram is equivalent to about 22 million kilowatt hours of heat energy. The complete detonation of a kilogram of plutonium produces an explosion equal to about 20,000 tons of chemical explosive.

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Plutonium

Its importance depends on the nuclear property of being readily fissionable with neutrons and its availability in quantity. The world's nuclear-power reactors are now producing about 20,000 kg of plutonium/yr. By 1982 it was estimated that about 300,000 kg had accumulated. The various nuclear applications of plutonium are well known. 238Pu has been used in the Apollo lunar missions to power seismic and other equipment on the lunar surface. As with neptunium and uranium, plutonium metal can be prepared by reduction of the trifluoride with alkaline-earth metals.

Properties

The metal has a silvery appearance and takes on a yellow tarnish when slightly oxidized. It is chemically reactive. A relatively large piece of plutonium is warm to the touch because of the energy given off in alpha decay. Larger pieces will produce enough heat to boil water. The metal readily dissolves in concentrated hydrochloric acid, hydroiodic acid, or perchloric acid. The metal exhibits six allotropic modifications having various crystalline structures. The densities of these vary from 16.00 to 19.86 g/cm3.

Hazards

Because of the high rate of emission of alpha particles and the element being specifically absorbed on bone the surface and collected in the liver, plutonium, as well as all of the other transuranium elements except neptunium, are radiological poisons and must be handled with very special equipment and precautions. Plutonium is a very dangerous radiological hazard. Precautions must also be taken to prevent the unintentional formulation of a critical mass. Plutonium in liquid solution is more likely to become critical than solid plutonium. The shape of the mass must also be considered where criticality is concerned.

Isotope

Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.

Last Updated: 12/19/97, CST Information Services Team

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Americium

Americium

For crystal research.

History

(the Americas) Americium was the fourth transuranic element to be discovered; the isotope 241Am was identified by Seaborg, James, Morgan, and Ghiorso late in 1944 at the wartime Metallurgical Laboratory of the University of Chicago as the result of successive neutron capture reactions by plutonium isotopes in a nuclear reactor. The luster of freshly prepared americium metal is white and more silvery than plutonium or neptunium prepared in the same manner. It appears to be more malleable than uranium or neptunium and tarnishes slowly in dry air at room temperature. Americium must be handled with great care to avoid personal contamination. The alpha activity from 241Am is about three times that of radium. When gram quantities of 241Am are handled, the intense gamma activity makes exposure a serious problem. 241Am has been used as a portable source for gamma radiography. It has also been used as a radioactive glass thickness gauge for the flat glass industry and as a source of ionization for smoke detectors.

Isotope

Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.

Last Updated: 12/19/97, CST Information Services Team

http://pearl1.lanl.gov/periodic/elements/95.html [3/6/2001 8:38:24 AM]