Neptunium

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Neptunium is a chemical element with the element symbol Np and atomic number 93 in the periodic table it is in the group of actinides (7th period, f-block ). Neptunium is the first of the so-called transuranic elements found on Earth, except for traces of neptunium and plutonium, not more, of course. Neptunium is a toxic and radioactive heavy metal. It was named after the planet Neptune, following the planet Uranus. Follows neptunium in the periodic table on uranium, followed by plutonium, the most difficult on earth naturally occurring element with atomic number 94

• 3.1 Physical Properties
• 3.2 Chemical Properties
• 3.3 Biological Aspects

• 7.1 oxides
• 7.2 halides
• 7.3 Organometallic Compounds

History

In May 1934, Ida Noddack expressed to the then existing gaps in the periodic table of the elements and placed at the end of their work reflect on the possibility of transuranium elements in. A few weeks later, Enrico Fermi published three papers on this topic. Noddack sat critical in September 1934 with the supposed discovery of element 93 by Fermi apart. In her remarks she took, inter alia, the discovery of the neutron- induced fission in advance: "It is conceivable that decompose at the bombardment of heavy nuclei with neutrons these nuclei into several large fragments which, although isotopes of known elements, but not neighbors of the irradiated elements. "

The radioactive element neptunium was first synthesized in 1940 by Edwin M. McMillan and Philip H. Abelson in the bombardment of uranium with neutrons.

Arthur C. Election and Glenn T. Seaborg discovered 1942 Neptuniumisotop 237Np. It arises from 237U, which is a β - emitter with around 7 days half-life; it is from 238U by a (n, 2n ) process is formed. 237Np is an α - emitter with a half -life of 2.144 x 106 years.

In 1950, the Neptuniumisotope 231Np, 232Np and 233Np were produced from 233U, 235U and 238U by bombardment with deuterons. In 1958, the Neptuniumisotope 234Np, 235Np and 236Np were generated from highly enriched 235U by bombardment with deuterons. 1 hour neptunium activity, which has been previously assigned to the 241Np however belongs to the isotope 240Np.

Production and representation

Extraction of Neptuniumisotopen

Neptunium is produced as a " byproduct " of energy in nuclear reactors. A ton of spent nuclear fuel is to contain 500 g of neptunium. So arisen neptunium consists almost entirely of the isotope 237Np. It arises from the uranium isotope 235U by double neutron capture and subsequent β -decay.

Representation of elementary neptunium

Metallic neptunium can be obtained by reduction from its compounds. First neptunium was reacted with elemental barium, or lithium at 1200 ° C to the reaction (III ) fluoride.

Properties

Physical Properties

Neptuniummetall has a silvery appearance, is chemically reactive, and exists in at least three different modifications:

Neptunium has one of the highest densities of all elements. In addition to rhenium, osmium, iridium and platinum, it is one of the few items that have a higher density than 20 g/cm3.

Chemical Properties

Neptunium is a series of compounds in which it may be present in the oxidation state 3 to 7. This forms neptunium together with plutonium, the highest oxidation state of all actinides. In aqueous solution, the Neptuniumionen have characteristic colors, the Np3 ion is purple-violet, NP4 yellow green, NpVO2 green, pink and NpVIIO23 NpVIO22 deep green.

Biological Aspects

A biological function of the neptunium is not known. Anaerobic microorganisms by means of Mn ( II / III) - and Fe reduced to Np (IV), (II ) species, Np (V). Further, the factors were examined, which affect the biosorption and bioaccumulation of neptunium by bacteria.

Isotopes

From a total of 20 isotopes and neptunium 5 Kernisomere are known. The most long-lived isotopes 237Np with 2.144 million years, 236Np and 235Np 154,000 years with half-life of 396.1 days. The remaining isotopes have half-lives and Kernisomere between 45 nanoseconds ( 237m1Np ) and 4.4 days ( 234Np ).

• 235Np decays with half-life of 396.1 days in 99.99740 % of cases by electron capture to uranium 235U and 0.00260 % of cases by alpha decay to protactinium 231Pa, which is one level on the uranium - actinium series behind 235U.

• 236Np decays with half-life of 154,000 years in 87.3 % of cases by electron capture to uranium 236U, in 12.5 % of cases by beta decay to plutonium 236Pu and in 0.16 % of cases by alpha decay to protactinium 232Pa. The uranium 236U is on the thorium series and decays with 23.42 million years to its official Anfangsnuklid thorium 232Th. 236Pu which decays with a half-life of 2,858 years by α - decay of the intermediate stage 232U, which decomposes to 228Th with a half-life of 68.9 years, it is on the main branch of the row.

• 237Np decays with 2.144 million years half-life by alpha decay to protactinium 233Pa. 237Np is the official starting point of the neptunium series, a decay chain that ends with thallium 205Tl isotope.

Fissionability

As with all transuranic nuclides the neutron-induced fission is also possible for the NP- isotopes. The isotopes with an odd number of neutrons in the nucleus - of the long-lived 236Np So - have large cross sections for the fission by thermal neutrons; the 236Np he is 2600 Barn, so it is " easy to split ."

The arising in nuclear reactor fuel 237Np this cross section is only 20 millibarn. However, this isotope is suitable because physical properties of other core to maintain the fission by fast neutrons in a pure material, a chain reaction. In the Los Alamos National Laboratory critical mass has been determined experimentally to about 60 kg. Therefore, 237Np is a potential material for nuclear weapons.

Use

The bred in nuclear reactors from 235U 237Np can be used for the production of 238Pu for use in radionuclide. There is (along with minor amounts of other Neptuniumisotope ) separated from the spent nuclear reactor fuel, and filled into the fuel rods, which contain only neptunium. They are re-inserted into the nuclear reactor where they are again irradiated with neutrons; from the 237Np 238Pu is bred.

Compounds

→ Category: Neptuniumverbindung

Oxides

Oxides are known in the stages 4 to 6: neptunium (IV ) oxide ( NpO2 ), neptunium (V ) oxide ( Np2O5 ) and neptunium (VI ) oxide ( NpO3 · H2O). Neptuniumdioxid ( NpO2 ) is chemically stable oxide of neptunium and is used in nuclear fuel rods.

Halides

For neptunium halides are known in the oxidation states 3 to 6.

For state 3, all compounds of the four halogens fluorine, chlorine, bromine and iodine are known. In addition, it forms halides in the stages 4 to 6.

In the 6 oxidation state is the Neptuniumhexafluorid ( NpF6 ) is of particular importance. It is an orange -colored solid with very high volatility, which merges already at 56 ° C in the gaseous state. In this capacity, it is very similar to uranium hexafluoride and plutonium hexafluoride, so it can be used as well in the enrichment and isotope separation.

Organometallic Compounds

Analogous to uranocene, an organometallic compound is complexed in the uranium of two cyclooctatetraene ligands, the corresponding complexes of thorium, protactinium, plutonium, americium and neptunium, ( η8 - C8H8 ) 2Np were represented.

Safety

Classifications according to the Hazardous Substances Ordinance are not available because they only include the chemical danger and play a very minor role compared to the risks based on the radioactivity.