neptunium

neptunium

a silvery metallic transuranic element synthesized in the production of plutonium and occurring in trace amounts in uranium ores. Symbol: Np; atomic no.: 93; half-life of most stable isotope, ²³⁷Np: 2.14 × 10⁶ years; valency: 3, 4, 5, or 6; relative density: 20.25; melting pt.: 639?1?C; boiling pt.: 3902?C (est.)

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

neptunium

[nep′tü·nē·əm]

(chemistry)

A chemical element, symbol Np, atomic number 93, atomic weight 237.0482; a member of the actinide series of elements.

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 It might be outdated or ideologically biased.

Neptunium

 

Np, an artificially produced radioactive chemical element of the actinide group. Atomic number, 93; atomic weight, 237.0482. It was discovered in 1940 by the American scientists E. M. McMillan and P. H. Abelson, who determined that the uranium isotope ²³⁹U, which forms during neutron bombardment of ²³⁸U, decays rapidly, emitting a β-particle, and is converted into an isotope of the element with atomic number 93. The element was named after the planet Neptune.

By 1973, 15 neptunium isotopes had been obtained; ²³⁷Np has the longest half-life (α-emitter; T_½ = 2.14 × 10⁶ yr). The β- radioactive isotope ²³⁹ Np (T_½ = 2.346 days) is widely used in research. The successive transformations of the isotope ²³⁷Np yield the stable isotope ²⁰⁹Bi; this chain of transformations is called the neptunium radioactive series. Negligible quantities of ²³⁷Np and ²³⁹Np are found in uranium ores, where they are continuously formed as a result of nuclear interactions of uranium atoms and neutrons.

Elementary neptunium is a malleable, relatively soft metal with a silver luster. Density, about 20 g/cm³; melting point, 640°C

The three outer electron shells of a neptunium atom have the configurations 5s²5p⁶, 5d¹⁰5f⁴, and 6s²6d¹ 7s²; the 5f-, 6d-, and 7s-electrons take part in the formation of neptunium compounds. The chemical properties of neptunium are very similar to those of uranium and plutonium. The oxidation numbers of neptunium compounds range from +2 to +7. In solution, neptunium produces the ions Np³⁺, Np⁴⁺, NpO₂⁺ (the most stable), NpO₂²⁺, and NpO₅^3-; all neptunium ions tend toward hydrolysis and complexing.

Ponderable quantities of isotope ²³⁷Np are formed as a byproduct during the production of plutonium in nuclear reactors through nuclear reactions of uranium and neutrons. Neptunium is mainly used in scientific research.

REFERENCE

Mikhailov, V. A. Analiticheskaia khimiia neptuniia. Moscow, 1971. (See also References under ACTINIDES.)

S. S. BERDONOSOV

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