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| {{Infobox neptunium}}
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| '''Neptunium''' is a [[chemical element]] with the symbol '''Np''' and [[atomic number]] 93. A [[radioactivity|radioactive]] [[actinide]] metal, neptunium is the first [[transuranic element]]. Its position in the periodic table just after [[uranium]], named after the planet [[Uranus]], led to its being named after [[Neptune]], the next planet beyond Uranus. A neptunium atom has 93 [[proton]]s and 93 electrons, of which seven are [[valence electron]]s. Neptunium metal is silvery and [[tarnish]]es when exposed to air. It occurs in three [[allotrope|allotropic]] forms. The element normally exhibits five [[oxidation state]]s, ranging from +3 to +7.
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| In the 1870s, [[Dmitri Mendeleev]] first predicted the existence of neptunium, and many false claims of its discovery were made over the years. The element was first synthesized by [[Edwin McMillan]] and [[Philip H. Abelson]] at the [[Berkeley Radiation Laboratory]] in 1940. Most neptunium is produced by bombarding uranium with neutrons in nuclear reactors; neptunium is also generated as a by-product in conventional [[nuclear reactor]]s. Though neptunium has no commercial uses at present, it is widely used as a precursor for the formation of [[plutonium-238]], used in [[radioisotope thermal generator]]s which are used to power some [[spacecraft]]. Neptunium itself can be used in [[neutron detector|detector]]s of high-energy [[neutron]]s.
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| The most stable [[isotope]] of neptunium, neptunium-237, is a by-product of [[nuclear reactor]]s and [[plutonium]] production, and it can be used as a component in [[neutron detection]] equipment. The isotopes neptunium-237 and neptunium-239 are also found in trace amounts in [[uranium]] ores due to [[neutron capture|neutron capture reactions]] and [[beta decay]].<ref name=CRC>{{cite book| author = C. R. Hammond |title = The Elements, in Handbook of Chemistry and Physics 81st edition| publisher =CRC press| isbn = 0-8493-0485-7| year = 2004}}</ref>
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| ==History==
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| ===Pre-discovery===
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| Even before its discovery, the existence of neptunium had been predicted several times. The periodic table of [[Dmitri Mendeleev]] published in the 1870s showed a " — " in place after uranium similar to several other places for at that point undiscovered elements. Also, a 1913 publication of the known radioactive isotopes by [[Kasimir Fajans]] shows the empty place after uranium.<ref>{{cite journal | last1 = Fajans | first1 = Kasimir | title = Die radioaktiven Umwandlungen und das periodische System der Elemente | journal = Berichte der deutschen chemischen Gesellschaft | volume = 46 | pages = 422 | year = 1913 | doi = 10.1002/cber.19130460162}}</ref>
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| The search for element 93 in minerals was encumbered by the fact that the predictions on the chemical properties of element 93 were based on a periodic table which lacked the actinide series, and therefore placed [[thorium]] below [[hafnium]], [[protactinium]] below [[tantalum]], and uranium below [[tungsten]]. This periodic table suggested that element 93, at that point often named [[Mendeleev's predicted elements|eka]]-[[rhenium]], should be similar to [[manganese]] or rhenium. With this misconception it was impossible to isolate element 93 from minerals, although neptunium was later found in uranium ore, in 1952.<ref>{{cite journal | last1 =Peppard | first1 =D. F. | last2 =Mason | first2 =G. W. | last3 =Gray | first3 =P. R. | last4 =Mech | first4 =J. F. | journal =Journal of the American Chemical Society | volume =74 | pages =6081 | year =1952 | doi =10.1021/ja01143a074 | issue =23}}</ref>
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| In 1934, [[Odolen Koblic]] extracted a small amount of material from the wash water of roasted [[pitchblende]]. He assumed the sample was element 93, and called it [[bohemium]], but after being analyzed, it turned out that the sample was a mixture of [[tungsten]] and [[vanadium]].<ref name=emsley/>
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| In 1938, [[Horia Hulubei]], a Romanian physicist; and [[Yvette Cauchois]], a French chemist; claimed to have discovered element 93 via [[spectroscopy]] in minerals. They named their element [[sequanium]], but the claim was opposed at the time because neptunium was thought to occur exclusively artificially. However, as neptunium does occur in nature, it is possible that Hulubei and Cauchois did in fact discover neptunium.<ref name=emsley>{{cite book| last = Emsley| first = John| title = Nature's Building Blocks: An A-Z Guide to the Elements| edition = 1st| year = 2001| publisher = Oxford University Press| location = New York, NY| isbn = 978-019-850340-8 | pages=345–7}}</ref>
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| Enrico Fermi believed that bombarding [[uranium]] with neutrons and subsequent beta decay would lead to the formation of element 93. Chemical separation of the new formed elements from the uranium yielded material with low half-life, and, therefore, Fermi announced the discovery of a new element in 1934,<ref name="Fermi">{{cite journal | doi =10.1038/133898a0 | title =Possible Production of Elements of Atomic Number Higher than 92 | year =1934 | author =Fermi, E. | journal =Nature | volume =133 | pages =898 | bibcode=1934Natur.133..898F | issue =3372}}</ref> though this was soon found to be mistaken. Soon it was speculated<ref>{{cite journal|author=Ida Noddack|authorlink=Ida Noddack|year=1934|pages=653|title=Über das Element 93|volume=47|journal=Zeitschrift für Angewandte Chemie|url=http://www.chemteam.info/Chem-History/Noddack-1934.html|doi=10.1002/ange.19340473707|issue=37}}</ref> and later proven<ref>{{cite journal|last1=Meitner|first1=Lise|last2=Frisch|first2=O. R.|doi=10.1038/143239a0|title=Disintegration of Uranium by Neutrons: a New Type of Nuclear Reaction|year=1939|pages=239|volume=143|journal=Nature|url=http://www.nature.com/physics/looking-back/meitner/index.html|bibcode=1939Natur.143..239M|issue=3615}}</ref> that most of the material is created by [[nuclear fission]] of uranium by neutrons. Small quantities of neptunium had to be produced in [[Otto Hahn]]'s experiments in late 1930s as a result of decay of <sup>239</sup>U. Hahn and his colleagues experimentally confirmed production and chemical properties of <sup>239</sup>U, but were unsuccessful at isolating and detecting neptunium.<ref>{{cite journal|url=http://www.crownedanarchist.com/emc2/discovery_of_fission.doc|title=Discovery of fission|author=Otto Hahn|journal=Scientific American|year=1958}}</ref>
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| ===Discovery===
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| In 1939, [[Edwin McMillan]] did some preliminary work leading to the eventual discovery of element 93. [[Uranium trioxide]] was placed on paper together with [[aluminium]] or paper foils and the result was irradiated with neutrons from a [[cyclotron]]. Examination revealed the presence of two components, both [[beta decay]]ing: one turned out to be [[uranium-239]] (half-life 23 minutes), while the other could not be characterized firmly. [[Emilio Segrè]] contradictorily labelled the second component as having atomic number 93 but not being a transuranic element, also noting that it behaved similarly to the [[rare earth element]]s. This lack of confidence in labelling the product as transuranic was from the absence of any observed activity from the beta decay product of element 93.<ref>Yoshida et al., pp. 699–700</ref>
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| Neptunium (named for the planet [[Neptune]], the next [[planet]] out from [[Uranus]], after which [[uranium]] was named) was finally convincingly [[discovery of the chemical elements|discovered]] by [[Edwin McMillan]] and [[Philip H. Abelson]] in 1940 at the [[Berkeley Radiation Laboratory]] of the [[University of California, Berkeley]]. The team produced the neptunium [[isotope]] <sup>239</sup>Np (2.4 day [[half-life]]) by bombarding [[uranium]] with slow moving neutrons. It was the first [[transuranium element]] produced synthetically and the first [[actinide series]] transuranium element discovered.<ref name="EL93">{{cite journal| doi =10.1103/PhysRev.57.1185.2| title =Radioactive Element 93| year =1940| author =Mcmillan, Edwin| journal =Physical Review| volume =57| pages =1185| last2 =Abelson| first2 =Philip| issue =12|bibcode = 1940PhRv...57.1185M }}</ref>
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| :<math>\mathrm{^{238}_{\ 92}U\ +\ ^{1}_{0}n\ \longrightarrow \ ^{239}_{\ 92}U\ \xrightarrow[23 \ min]{\beta^-} \ ^{239}_{\ 93}Np\ \xrightarrow[2.355 \ d]{\beta^-} \ ^{239}_{\ 94}Pu}</math>
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| ==Occurrence==
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| The most stable isotope of neptunium is <sup>237</sup>Np, with a half-life of two million years. Thus, all primordial neptunium should have decayed by now. However, trace amounts of the neptunium isotopes neptunium-237 through neptunium-240, are found naturally as [[decay product]]s from [[Nuclear transmutation|transmutation]] reactions in [[uranium ore]]s.<ref name=CRC/><ref name=emsley/>
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| Artificial <sup>237</sup>Np is produced through a reaction of <sup>237</sup>NpF<sub>3</sub> with liquid [[barium]] or [[lithium]] at around 1200 °[[Celsius|C]] and is most often extracted from spent [[nuclear fuel rod]]s in kilogram amounts as a by-product in [[plutonium]] production.<ref name=emsley/>
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| :2 {{chem|NpF|3}} + 3 Ba → 2 Np + 3 {{chem|BaF|2}}
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| By weight, neptunium-237 discharges are about 5% as great as plutonium discharges and about 0.05% of [[spent nuclear fuel]] discharges.<ref>{{cite web| format=PDF| url = http://www.isis-online.org/publications/fmct/book/New%20chapter%205.pdf| title = Separated Neptunium 237 and Americium| accessdate = 2009-06-06}}</ref> However, even this fraction still amounts to more than fifty tons per year.<ref name="rsc">http://www.rsc.org/chemistryworld/podcast/interactive_periodic_table_transcripts/neptunium.asp</ref>
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| ==Characteristics==
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| Silvery in appearance, neptunium [[metal]] is chemically fairly [[chemical reaction|reactive]] and is found in at least three [[allotrope]]s:<ref name=CRC/>
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| * α-neptunium, [[orthorhombic]], density 20.45 g/cm<sup>3</sup><ref name = "alo">{{cite journal | last1 = Lee | first1 = J | last2 = Mardon | first2 = P | last3 = Pearce | first3 = J | last4 = Hall | first4 = R | title = Some physical properties of neptunium metal II: A study of the allotropic transformations in neptunium | journal = Journal of Physics and Chemistry of Solids | volume = 11 | pages = 177 | year = 1959 | doi = 10.1016/0022-3697(59)90211-2 | issue = 3–4|bibcode = 1959JPCS...11..177L }}</ref>
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| * β-neptunium (above 280 °C), [[tetragonal]], density (313 °C) 19.36 g/cm<sup>3</sup><ref name = "alo"/>
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| * γ-neptunium (above 577 °C), cubic, density (600 °C) 18 g/cm<sup>3</sup><ref name = "alo"/>
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| Neptunium has the largest liquid range of any element, 3363 K, between the melting point and boiling point. It is the densest of all the actinides and the fifth-densest of all naturally occurring elements.<ref>Theodore Gray. ''The Elements''. Page 215</ref> Neptunium has no biological role. It is not absorbed by the digestive tract. When injected into the body, it accumulates in [[bone]]s, from which it is slowly released.
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| ==Isotopes==
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| {{Main|Isotopes of neptunium}}
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| 19 neptunium [[radioisotope]]s have been characterized, with the most stable being <sup>237</sup>Np with a [[half-life]] of 2.14 million years, <sup>236</sup>Np with a half-life of 154,000 years, and <sup>235</sup>Np with a half-life of 396.1 days. All of the remaining [[radioactive]] isotopes have half-lives that are less than 4.5 days, and the majority of these have half-lives that are less than 50 minutes. This element also has 4 [[meta state]]s, with the most stable being <sup>236m</sup>Np (t<sub>½</sub> 22.5 hours).
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| The isotopes of neptunium range in [[atomic weight]] from 225.0339 [[atomic mass unit|u]] (<sup>225</sup>Np) to 244.068 u (<sup>244</sup>Np). The primary [[decay mode]] before the most stable isotope, <sup>237</sup>Np, is [[electron capture]] (with a good deal of [[alpha emission]]), and the primary mode after is [[beta emission]]. The primary [[decay product]]s before <sup>237</sup>Np are element 92 ([[uranium]]) isotopes (alpha emission produces element 91, [[protactinium]], however) and the primary products after are element 94 ([[plutonium]]) isotopes.
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| <sup>237</sup>Np is [[fissionable]].<ref name="critical" /> <sup>237</sup>Np eventually decays to form [[bismuth]]-209 and [[thallium]]-205, unlike most other common heavy nuclei which decay to make [[isotopes of lead]]. This [[decay chain]] is known as the [[neptunium series]].
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| ==Synthesis==
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| Chemically, neptunium is prepared by the reduction of NpF<sub>3</sub> with barium or lithium vapor at about 1200 °C.<ref name=CRC/> Most Np is produced in nuclear reactions:
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| * When an [[Uranium-235|<sup>235</sup>U]] atom captures a neutron, it is converted to an excited state of [[Uranium-236|<sup>236</sup>U]]. About 81% of the excited <sup>236</sup>U nuclei undergo fission, but the remainder decay to the ground state of <sup>236</sup>U by emitting [[gamma radiation]]. Further [[neutron capture]] creates <sup>237</sup>U which has a half-life of 7 days and thus quickly decays to <sup>237</sup>Np through [[beta decay]]. During beta decay, the excited <sup>237</sup>U emits an electron, while the atomic [[weak interaction]] converts a [[neutron]] to a [[proton]], thus creating <sup>237</sup>Np.
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| ::<math>\mathrm{^{235}_{\ 92}U\ +\ ^{1}_{0}n\ \longrightarrow \ ^{236}_{\ 92}U_m\ \xrightarrow[120 \ ns]{} \ ^{236}_{\ 92}U\ +\ \gamma}</math>
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| ::<math>\mathrm{^{236}_{\ 92}U\ +\ ^{1}_{0}n\ \longrightarrow \ ^{237}_{\ 92}U\ \xrightarrow[6.75 \ d]{\beta^-} \ ^{237}_{\ 93}Np}</math>
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| * <sup>237</sup>U is also produced via an ([[neutron|n]],2n) reaction with [[Uranium-238|<sup>238</sup>U]]. This only happens with very energetic neutrons.
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| * <sup>237</sup>Np is the product of [[alpha decay]] of [[Americium-241|<sup>241</sup>Am]].
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| Heavier isotopes of neptunium decay quickly, and lighter isotopes of neptunium cannot be produced by [[neutron capture]], so chemical separation of neptunium from cooled [[spent nuclear fuel]] gives nearly pure <sup>237</sup>Np.
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| ==Chemistry==
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| [[File:Np ox st .jpg|thumb|Neptunium ions in solution.]]
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| This element has five ionic [[oxidation state]]s while in solution:
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| * Np<sup>3+</sup> (pale purple), analogous to the rare earth ion Pm<sup>3+</sup>
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| * Np<sup>4+</sup> (yellow-green)
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| * {{chem|NpO|2|+}} (green-blue)
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| * {{chem|NpO|2|2+}} (pale pink)
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| * {{chem|NpO|5|3-}} (green). This may better be labelled as a hydroxo species {{chem|[NpO|4|(OH)|2|]|3-}}.
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| Neptunium(III) hydroxide is not soluble in water and does not dissolve in excess alkali. Neptunium(III) is susceptible to oxidation in contact to air forming neptunium(IV).<ref>{{cite book | url = http://books.google.de/books?id=1lArAAAAYAAJ | title = Radiochemistry of neptunium | author1 = Burney, G. A | author2 = Harbour, R. M | author3 = Subcommittee On Radiochemistry, National Research Council (U.S.) | author4 = Technical Information Center, U.S. Atomic Energy Commission | year = 1974}}</ref><ref>{{cite book | url =http://books.google.de/books?id=UnQ_NQAACAAJ | title =The migration chemistry of neptunium | isbn =978-87-550-1535-7 | author1 =Nilsson, Karen | year =1989}}</ref>
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| Neptunium forms tri- and tetra[[halide]]s such as NpF<sub>3</sub>, NpF<sub>4</sub>, NpCl<sub>4</sub>, NpBr<sub>3</sub>, NpI<sub>3</sub>, and [[oxide]]s of the various compositions such as are found in the uranium-[[oxygen]] system, including Np<sub>3</sub>O<sub>8</sub> and [[Neptunium(IV) oxide|NpO<sub>2</sub>]].
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| [[Neptunium hexafluoride]], NpF<sub>6</sub>, is volatile like [[uranium hexafluoride]].
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| {{Further|fluoride volatility|uranium enrichment}}
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| Neptunium, like [[protactinium]], [[uranium]], [[plutonium]], and [[americium]] readily forms a linear dioxo neptunyl core (NpO<sub>2</sub><sup>n+</sup>), in its 5+ and 6+ oxidation states, which readily complexes with hard O-donor ligands such as OH<sup>–</sup>, NO<sub>2</sub><sup>–</sup>, NO<sub>3</sub><sup>–</sup>, and SO<sub>4</sub><sup>2–</sup> to form soluble anionic complexes which tend to be readily mobile with low affinities to soil. Neptunium is very reactive when in contact with [[oxygen]], [[steam]], or [[acid]]. However it is not attacked by [[alkali]]s.<ref name = emsley/>
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| * NpO<sub>2</sub>(OH)<sub>2</sub><sup>–</sup>
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| * NpO<sub>2</sub>(CO<sub>3</sub>)<sup>–</sup>
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| * NpO<sub>2</sub>(CO<sub>3</sub>)<sub>2</sub><sup>3–</sup>
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| * NpO<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub><sup>5–</sup>
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| {{See also|Actinides in the environment}}
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| ==Applications==
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| ===Precursor in plutonium-238 production===
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| <sup>237</sup>Np is irradiated with neutrons to create [[Plutonium 238|<sup>238</sup>Pu]], an [[alpha emitter]] for [[radioisotope thermal generator]]s for spacecraft and military applications. <sup>237</sup>Np will capture a neutron to form <sup>238</sup>Np and [[beta decay]] with a half-life of two days to <sup>238</sup>Pu.<ref>{{cite journal|doi = 10.1016/j.enconman.2007.10.028|pages = 393–401|title = Review of recent advances of radioisotope power systems|year = 2008|author = Lange, R|journal = Energy Conversion and Management|volume = 49|last2 = Carroll|first2 = W|issue = 3}}</ref>
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| :<math>\mathrm{^{237}_{\ 93}Np\ +\ ^{1}_{0}n\ \longrightarrow \ ^{238}_{\ 93}Np\ \xrightarrow[2.117 \ d]{\beta^-} \ ^{238}_{\ 94}Pu}</math>
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| <sup>238</sup>Pu also exists in sizable quantities in [[spent nuclear fuel]] but would have to be separated from other [[isotopes of plutonium]].
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| ===Weapons applications===
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| Neptunium is [[fissionable]], and could theoretically be used as fuel in a [[fast neutron reactor]] or a [[nuclear weapon]], with a [[critical mass]] of around 60 kilograms.<ref name="rsc" /> In 1992, the [[U.S. Department of Energy]] declassified the statement that neptunium-237 "can be used for a nuclear explosive device".<ref name="RDD-7">[http://www.fas.org/sgp/othergov/doe/rdd-7.html "Restricted Data Declassification Decisions from 1946 until Present"], accessed Sept 23, 2006</ref> It is not believed that an actual weapon has ever been constructed using neptunium. As of 2009, the world production of neptunium-237 by commercial power reactors was over 1000 critical masses a year, but to extract the isotope from irradiated fuel elements would be a major industrial undertaking.
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| In September 2002, researchers at the [[Los Alamos National Laboratory]] briefly created the first known nuclear [[critical mass]] using neptunium in combination with shells of [[enriched uranium]] ([[U-235]]), discovering that the critical mass of a bare sphere of neptunium-237 "ranges from kilogram weights in the high fifties to low sixties,"<ref name="critical1"/> showing that it "is about as good a bomb material as [[Uranium-235|U-235]]."<ref name="critical">{{cite web|last = Weiss|first = P.|title = Little-studied metal goes critical – Neptunium Nukes?| publisher = [[Science News]] |date = October 26, 2002|url = http://www.findarticles.com/p/articles/mi_m1200/is_17_162/ai_94011322|accessdate = 2006-09-29}}</ref> The United States Federal government made plans in March 2004 to move America's supply of separated neptunium to a nuclear-waste disposal site in [[Nevada]].
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| ===Physics applications===
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| <sup>237</sup>Np is used in devices for detecting high-energy (MeV) neutrons.<ref>{{cite book| page =236| title =Experimental techniques in nuclear physics|
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| author = [[Dorin N Poenaru]], [[Walter Greiner]]| publisher =Walter de Gruyter| year = 1997| isbn =3-11-014467-0}}</ref>
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| <!--{{cite journal|doi = 10.1016/0375-9474(72)90778-6|title = The energy dependence of the fissionability of neptunium isotopes and the level density of highly deformed nuclei|year = 1972|author = Bishop, C|journal = Nuclear Physics A|volume = 198|pages = 161 |bibcode = 1972NuPhA.198..161B|last2 = Halpern|first2 = I.|last3 = Shaw|first3 = R.W.|last4 = Vandenbosch|first4 = R. }} {{cite book|url = http://books.google.com/?id=V1cwK1ehoYcC&pg=PT40|isbn = 978-3-527-32065-3|author = Hans-Jürgen Quadbeck-Seeger ; translated by José Oliveira.|year = 2007|publisher = Wiley-VCH|location = Weinheim|title = World of the elements : elements of the world}} -->
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| ==Role in nuclear waste==
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| Neptunium-237 is the most mobile [[actinide]] in the [[deep geological repository]] environment.<ref>{{cite web| url = http://www.fas.org/sgp/othergov/doe/lanl/pubs/00818052.pdf| title= Yucca Mountain| accessdate = 2009-06-06}}</ref>
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| This makes it and its predecessors such as [[americium-241]] candidates of interest for destruction by [[nuclear transmutation]].<ref>{{cite journal| doi =10.1016/S0029-5493(03)00034-7| title =Deep-Burn: making nuclear waste transmutation practical| year =2003| author =Rodriguez, C| journal =Nuclear Engineering and Design| volume =222| pages =299| issue =2–3| last2 =Baxter| first2 =A.| last3 =McEachern| first3 =D.| last4 =Fikani| first4 =M.| last5 =Venneri| first5 =F.}}</ref> Neptunium accumulates in commercial household ionization-chamber [[smoke detector]]s from decay of the (typically) 0.2 [[microgram]] of americium-241 initially present as a source of [[ionizing radiation]]. With a half-life of 432 years, the americium-241 in a smoke detector includes about 3% neptunium after 20 years, and about 15% after 100 years.
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| Due to its long half-life, neptunium becomes the major contributor of the total radiation in 10,000 years. As it is unclear what happens to the containment in that long time span, an extraction of the neptunium would minimize the contamination of the environment if the nuclear waste could be mobilized after several thousand years.<ref>{{cite web|url = http://newscenter.lbl.gov/feature-stories/2005/11/29/getting-the-neptunium-out-of-nuclear-waste/|date =2005-11-29| title = Getting the Neptunium out of Nuclear Waste|first = Lynn|last = Yarris|publisher = Berkeley laboratory, U.S. Department of Energy|accessdate = 05-12-2008}}</ref><ref>{{cite web|url = http://www.pnl.gov/main/publications/external/technical_reports/PNNL-14307.pdf|title = Existing Evidence for the Fate of Neptunium in the Yucca Mountain Repository|author = J. I. Friese; E. C. Buck; B. K. McNamara; B. D. Hanson; S. C. Marschman|date = January 6, 2003|publisher = Pacific northwest national laboratory, U.S. Department of Energy|accessdate = 05-12-2008}}</ref><!--{{doi|10.1002/anie.200501281}}-->
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| <!--annual production 4.6 tonnes http://books.google.de/books?hl=de&lr=&id=oFtPmEPqjCgC&oi=fnd&pg=PA79-->
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| ==Biological role and precautions==
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| Neptunium does not have any biological role. It is absorbed via the [[digestive tract]]. When injected it concentrates in the bones, from which it is slowly released.<ref name=emsley/>
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| ==References==
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| {{Reflist|2}}
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| ==Bibliography==
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| * {{cite book|first1 = Zenko|last1 = Yoshida|first2 = Stephen G.|last2 = Johnson|first3 = Takaumi|last3 = Kimura|first4 = John R.|last4=Krsul|ref=Yoshida et al.|contribution = Neptunium|title = The Chemistry of the Actinide and Transactinide Elements|editor1-first = Lester R.|editor1-last = Morss|editor2-first = Norman M.|editor2-last = Edelstein|editor3-first = Jean|editor3-last = Fuger|edition = 3rd|year = 2006|volume = 3|publisher = Springer|location = Dordrecht, the Netherlands|pages = 699–812|url = http://radchem.nevada.edu/classes/rdch710/files/neptunium.pdf|doi = 10.1007/1-4020-3598-5_6}}
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| ==Literature==
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| * ''Guide to the Elements – Revised Edition'', Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1
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| * Lester R. Morss, Norman M. Edelstein, Jean Fuger (Hrsg.): ''The Chemistry of the Actinide and Transactinide Elements'', Springer-Verlag, Dordrecht 2006, ISBN 1-4020-3555-1.
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| * {{cite journal|author=Ida Noddack|authorlink=Ida Noddack|year=1934|pages=653|title=Über das Element 93|volume=47|journal=Zeitschrift für Angewandte Chemie|url=http://www.chemteam.info/Chem-History/Noddack-1934.html|doi=10.1002/ange.19340473707|issue=37}}
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| * Eric Scerri, A Very Short Introduction to the Periodic Table, Oxford University Press, Oxford, 2011, ISBN 978-0-19-958249-5.
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| ==External links==
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| {{Commons|Neptunium}}
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| {{Wiktionary|neptunium}}
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| * [http://www.periodicvideos.com/videos/093.htm Neptunium] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
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| * [http://www.eurekalert.org/features/doe/2001-08/danl-lbw060502.php Lab builds world's first neptunium sphere], [[U.S. Department of Energy]] Research News
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| * [http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+@rel+neptunium,+radioactive NLM Hazardous Substances Databank – Neptunium, Radioactive]
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| * [http://www.ead.anl.gov/pub/doc/neptunium.pdf Neptunium: Human Health Fact Sheet]
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| * [http://pubs.acs.org/cen/80th/neptunium.html C&EN: It's Elemental: The Periodic Table – Neptunium]
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| {{Clear}}
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| {{compact periodic table}}
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| {{Neptunium compounds}}
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| {{Chemical elements named after places}}
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| [[Category:Actinides]]
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| [[Category:Chemical elements]]
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| [[Category:Neptunium]]
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| [[Category:Synthetic elements]]
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| {{link FA|pl}}
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