(Planet Neptune) Neptunium was the first synthetic transuranium element of the actinideseries discovered; the isotope 239Np was produced by McMillan and Abelson in 1940 atBerkeley, California, as the result of bombarding uranium with cyclotron-producedneutrons. The isotope 237Np (half-life of 2.14 x 106 years) is currently obtained in gramquantities as a by-product from nuclear reactors in the production of plutonium. Tracequantities of the element are actually found in nature due to transmutation reactions inuranium ores produced by the neutrons which are present. Neptunium is prepared by thereduction of NpF3 with barium or lithium vapor at about 1200C. Neptunium metal has asilvery appearance, is chemically reactive, and exists in at least three structuralmodifications: 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 statesin solution: Np+3 (pale purple), analogous to the rare earth ion Pm+3, Np+4 (yellowgreen); NpO+ (green blue): and NpO++ (pale pink). These latter oxygenated species are incontrast to the rare earths which exhibit only simple ions of the (II), (III), and (IV)oxidation states in aqueous solution. The element forms tri- and tetrahalides such asNpF3, NpF4, NpCl4, NpBr3, NpI3, and oxides of the various compositions such as are foundin the uranium-oxygen system, including Np3O8 and NpO2. Fifteen isotopes of neptunium arenow 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 ata price of $280/g.