Properties of Neptunium

amu Half-Ufe Radioactive decay Reaction with 2200 m/s neutrons 

Transition temperature, °C Phase Crystal system Density, g/cm  

Source C. Keller, The Chemistry of the Transuranium Elements, Verlag Chemie, Weinheim, 1971. 

The phases of metallic neptunium, and their densities and tranation temperatures, are listed in Table 9.12. 

Metallic neptunium is prepared by reducing Npp4 with calcium. Neptunium yields of about 99 percent have been obtained from 100- to 400-g quantities of NpF4, with 30 percent excess calcium and with 0.25 to 035 mol of iodine booster per mole of Npp4. Metallic neptunium forms a protective oxide layer in air at room temperature, but it rapidly oxidizes at higher temperatures. It dissolves readily in HCl and H2 SO4 [K2]. 

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Since this is so, it was inevitable that as soon as Seaborg and his collaborators had clearly established the identity and properties of neptunium and plutonium, they would look for the next higher elements, numbers 95 and 96. The general similarity in chemical properties of uranium, neptunium, and plutonium led Seaborg to believe that these new elements could be isolated by methods similar to those already used. 

A lot of new coordination Np(V) complexes are still synthesized and several types of a novel CCB network have been found in their crystal structure [58-61]. Magnetic study is also performed about some neptunyl(+l) complexes [62], but there is no application of Np Mossbauer spectroscopy to them. Np Mossbauer spectroscopy is a very powerful and indispensable tool to study the electronic and the magnetic properties of neptunium complexes and will give several important information that cannot be provided with the magnetization measurement. Now Np Mossbauer spectroscopy is hardly performed due to the severe restrictions in handling transuranic materials and the output in this field is markedly reduced [63] however, many unsolved problems in this field that one should work on are left uncompleted. 

Initially, the only means of obtaining elements higher than uranium was by a-particle bombardment of uranium in the cyclotron, and it was by this means that the first, exceedingly minute amounts of neptunium and plutonium were obtained. The separation of these elements from other products and from uranium was difficult methods were devised involving co-precipitation of the minute amounts of their salts on a larger amount of a precipitate with a similar crystal structure (the carrier ). The properties were studied, using quantities of the order of 10 g in volumes of... 

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. 

The chemistry of plutonium is unique in the periodic table. This theme is exemplified throughout much of the research work that is described in this volume. Many of the properties of plutonium cannot be estimated accurately based on experiments with lighter elements, such as uranium and neptunium. Because massive amounts of plutonium have been and are being produced throughout the world, the need to define precisely its chemical and physical properties and to predict its chemical behavior under widely varying conditions will persist. In addition to these needs, there is an intrinsic fundamental interest in an element with so many unusual properties and with so many different oxidation states, each with its own chemistry. 

That magnetic measurements often raise more problems than they solve, is demonstrated for the indicated compound. We prepared a series of [ (C2H5N] i,An(NSC) e compounds (An = Th, U, Np, Pu) with cubic coordination of the actinide ion. We derived a consistent interpretation of the magnetic and optical properties of the uranium and the neptunium compounds (6 ). In the case of Pu we expect an isolated T1 ground state and a first excited state at about 728 cm-1. To our surprise we found a magnetic ground state much more pronounced than in the case of the hexachloro-complex, Fig. 4. 

Neptunium (Np), 1 463-491, 464t electronic configuration, i 474t ion type and color, l 477t metal properties of, l 482t Neral, 24 530... 

The first actinide metals to be prepared were those of the three members of the actinide series present in nature in macro amounts, namely, thorium (Th), protactinium (Pa), and uranium (U). Until the discovery of neptunium (Np) and plutonium (Pu) and the subsequent manufacture of milligram amounts of these metals during the hectic World War II years (i.e., the early 1940s), no other actinide element was known. The demand for Pu metal for military purposes resulted in rapid development of preparative methods and considerable study of the chemical and physical properties of the other actinide metals in order to obtain basic knowledge of these unusual metallic elements. 

C. Licour, L. Lopes, Contribution to the Knowledge of the Electrochemical Properties of Actinides in Non-Aqueous Media III. The Reduction of Tetravalent Thorium and Tetravalent Neptunium in Various Organic Solvents, Pages 6-12, 1995, with permission from Elsevier). 

All the early work on plutonium was done with unweighable amounts on a tracer scale. When it became apparent that large amounts would be needed for the atomic bomb, it was necessary to have a more detailed knowledge of the chemical properties of this element. Intensive bombardment of hundreds of pounds of uranium was therefore begun in the cyclotrons at Berkeley and at Washington University in St. Louis. Sepa-ration of plutonium from neptunium was based on the fact that neptunium is oxidized by bromate while plutonium is not, and that reduced fluorides of the two metals are carried down by precipitation of rare earth fluorides, while the fluorides of the oxidized states of the two elements are not. Therefore a separation results by repeated bromate oxidations and precipitations with rare earth fluorides. 

The lower oxidation states are more stable than those of neptunium (59). Much that is known has not been disclosed, but the information is slowly emerging. Thus, only in 1954 was it revealed that the metallurgists at Los Alamos in 1945 knew that plutonium metal had the unique property of possessing at least five allotropic modifications at atmospheric pressure (74). 

Peretrukhin, V. F. Alekseeva, D. P., "Polarographic Properties of Higher Oxidation States of Neptunium in Aqueous Alkaline Media, Sov. Radiochem., 1974, 16, 816-822. 

The actinides plutonium, neptunium, protoactinium, and thorium (151,173) bind to transferrin. The larger Th4+ ion (radius, 0.94 A) still binds to both sites, although binding to the second site (probably the N-terminal site) is significantly weaker than that to the first and apparently involves only one Tyr ligand compared with two Tyr in the other (151). Although UV difference spectra for Pu4+ are equivocal (174), it seems likely that two Pu4+ are bound. The likely carrier properties of transferrin for Pu4+ makes the design of competitive chelators of some importance (151). 

Americium. The low solubilities and high sorption affinity of thorium and americium severely limit their mobility under environmental conditions. However, because each exists in a single oxidation state—Th(IV) and Am(III)— under environmentally relevant conditions, they are relatively easy to study. In addition, their chemical behaviors provide valuable information about the thermodynamic properties of trivalent and tetravalent species of uranium, neptunium, and plutonium. 

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