Neptunium system

The Table shows a great spread in Kd-values even at the same location. This is due to the fact that the environmental conditions influence the partition of plutonium species between different valency states and complexes. For the different actinides, it is found that the Kd-values under otherwise identical conditions (e.g. for the uptake of plutonium on geologic materials or in organisms) decrease in the order Pu>Am>U>Np (15). Because neptunium is usually pentavalent, uranium hexavalent and americium trivalent, while plutonium in natural systems is mainly tetravalent, it is clear from the actinide homologue properties that the oxidation state of plutonium will affect the observed Kd-value. The oxidation state of plutonium depends on the redox potential (Eh-value) of the ground water and its content of oxidants or reductants. It is also found that natural ligands like C032- and fulvic acids, which complex plutonium (see next section), also influence the Kd-value. 

ICP-MS (inductively coupled plasma mass spectrometry) is frequently used for determining ultratrace amounts of technetium [9]. In spite of the high cost of the equipment, this detection method is far superior to other radiometric methods as regards sensitivity. When a double focussing high-resolution system is used (HR-ICP-MS) and an ultrasonic nebulizer is introduced [10], the detection limit is in the order 0.002 mBq. The ICP-MS method has been successfully applied to the determination of environmental "Tc as well as to other long-lived radionuclides of neptunium and plutonium in the environment. 

Neptunium - the atomic niunber is 93 and the chemical symbol is Np. The name derives from the planet Neptune (the Roman god of the sea), since it is the next outer-most planet beyond the planet uranus in the solar system and this element is the next one beyond uranium in the periodic table.lt was first synthesized by Edwin M. McMillan and Philip H. Abelson in 1940 via the nuclear reaction n, y) U P = p. The longest half-life associated with this mistable... 

Plutonium - the atomic number is. 94 and the chemical symbol is Pu. The name derives from the planet Pluto, (the Roman god of the underworld). Pluto was selected because it is the next planet in the solar system beyond the planet Neptime and the element plutonium is the next element in the period table beyond neptunium. Plutonium was first synthesized in 1940 by American chemists Glenn T. Seaborg, Edwin M. McMillan, Joseph W. Kennedy and Arthur C. Wahl in the nuclear reaction U( H, 2n) Np = P => Pu. The longest half-life associated with this unstable element is 80 million year Pu. 

Riglet, Ch. Robouch, P. Vitorge, P. Standard potentials of the (M02 /M0j) and redox systems for neptunium and plutonium. Radiochim. 

Of some interest is that after uranium ( jU) was named after the planet Uranus, neptunium (jjNp), which was discovered next, was named after Neptune, the next planet in our solar system. And Anally, plutonium (g4Pu) the next transuranic element discovered, was named after Pluto, the last planet discovered so far in our solar system. 

Neptunium, the first transuranium element, was discovered hy E. M. McMdlan and P. H. Ahelson in 1940 in Berkeley, California. It was produced in the cyclotron in a nuclear reaction by bombarding uranium-238 with neutrons. An isotope of mass 239 and atomic number 93 and ti/2 of 2.4 days was produced in this reaction. Neptunium-237, the longest-lived alpha-emitter with half-life 2.14x10 years, was discovered two years later in 1942 by Wahl and Seaborg. The new element was named after the planet Neptune, the planet next to Uranus in the solar system. 

A system particularly studied from a thermodynamic point of view is the monocarbide (AnCi x) system. A range of stability for carbon deficient compositions in the monocarbides is present in many metal-carbon phase diagrams. Table 6 shows the composition range at room temperature for actinide monocarbides. The non-stoichiometry range is very limited for uranium monocarbide for neptunium and plutonium monocarbides, the stoichiometric AmCj oo composition is not stable. 

This isotope had a half-life of about 24,000 years. It proved to be fissionable (56) and was the basis for the plutonium atomic bomb. Concentrated work on the new element was now begun by the Manhattan Project. The main work was done at Chicago. At this time it became desirable to have names for the elements which had previously been called simply 93 and 94 by the men who worked with them. The name suggested by McMillan, neptunium, was therefore adopted for 93, and by analogy 94 was named plutonium from the planet Pluto, next beyond Neptune in the solar system (53, 69). 

The neptunium oxide system exhibits complexity similar to that found in the uranium oxide system. Thus, the important oxide is NpCL and there exists a range of compositions, depending upon conditions, up to Np30g. 

Tochiyama, O., Nakamura, Y., Hirota, M., Inoue, Y. 1995. Kinetics of nitrous acid-catalyzed oxidation of neptunium in nitric acid - TBP extraction system. J. Nucl. Sci. Technol. 32 118-124. 

Recently, the SISAK technique has been applied for the separation of new, neutron-rich neptunium isotopes formed in direct transfer reactions between 8Xe projectiles and targets of Pu at the UNI LAC heavy-ion accelerator. The SISAK system consisted of three mixer-centrifuge units and a degasser. 

The hexavalent state of neptunium and plutonium are identical to that of U(VI), in the sense that both exist as M02+ in aqueous solutions. Whereas U(VI) is quite stable in aqueous solutions Np(VI) and Pu(VI) are unstable, especially when in contact with organic solutions, and need to be stabilized by using holding oxidants. Only a few studies have been reported for these systems. In the extraction with HTTA-B mixtures, the species M02(TTA)2 B was reported6, to be responsible for the observed synergism with both these ions, just like U(VI), and the equilibrium constant data are included in Table 7. It appears that the stabilities of the M02(TTA)2 B adducts of U(VI), Np(VI) and Pu(VI) are of, more or less, similar magnitude. 

Im System Neptunium-Bor konnten vier Boride nachgewiesen wer-den 147a), die mit den entsprechenden Verbindungen des Urans und Plutoniums isostrukturell sind ... 

Fig. 3 Potential-pH diagram of the neptunium-water system at 298 K with SnC>2 conduction band edge overlaid. Dissolved neptunium activity= 0.01...

Although PUCI4 has been well characterized in the gas phase (51) in the temperature range 670-1025 K, all attempts to obtain tTiTs compound in the solid state have failed. Use of a plot of the difference AHf(MCl4,c) - AHf(M , aq) (, 8) as a function of the actinide ionic radii ( ) (as done above for PuFa) in the case of thorium, protactinium, uranium and neptunium yields a first path leading to aH (PuC14,c). A second path involves the extrapolation to the plutonium system of the difference AH5o n( C 4 ) ... 

The studies on the neptunium nitride system are somewhat limited with the mononitride, NpN, being the predominant phase. PuN is also the only known componnd inthe plutoninm series. The AnN (An = Np, Pu) has been synthesized by reaction of an actinide hydride with NH3 at high temperatures. 

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