Protactinium,Uranium,Neptunium

Protactinium is a chemical element with the symbol Pa and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds where protactinium is usually present in the oxidation state +5, but can also assume +4 and even +2 or +3 states. The average concentrations of protactinium in the Earth's crust is typically on the order of a few parts per trillion, but may reach up to a few parts per million in some uraninite ore deposits. Sony A1258274A Battery

Because of the scarcity, high radioactivity and high toxicity, there are currently no uses for protactinium outside of scientific research, and for this purpose, protactinium is mostly extracted from spent nuclear fuel.

Protactinium was first identified in 1913 by Kasimir Fajans and Oswald Helmuth Göhring and named brevium because of the shorthalf-life of the specific isotope studied, namely protactinium-234. Sony VGP-BPL10 Battery

A more stable isotope of protactinium was discovered in 1918, and therefore the name was changed to protoactinium and then to protactinium in 1949. The new name meant "parent ofactinium" and reflected the fact that actinium is a product of radioactive decay of protactinium. Sony VGP-BPS10 Battery

The longest-lived and most abundant (nearly 100%) naturally occurring isotope of protactinium, protactinium-231, has a half-life of 32,760 years and is a decay product of uranium-235. Much smaller trace amounts of the short-lived nuclear isomerprotactinium-234m occur in the decay chain of uranium-238. Protactinium-233 results from the decay of thorium-233 as part of the chain of events used to produce uranium-233 by neutron irradiation of thorium-232. Sony VGP-BPS10/S Battery

It is an undesired intermediate product in thorium-based nuclear reactors and is therefore removed from the active zone of the reactor during the breeding process. Analysis of the relative concentrations of various uranium, thorium and protactinium isotopes in water and minerals is used in radiometric datingof sediments which are up to 175,000 years old and in modeling of various geological processes. Sony VGP-BPS10A/B Battery

In 1871, Dmitri Mendeleev predicted the existence of an element between thorium and uranium.^[3] The actinide element group was unknown at the time. Therefore, uranium was positioned below tungsten, and thorium below zirconium, leaving the space below tantalum empty, and until the 1950s periodic tables were published with this structure.^[4] Sony VGP-BPS10B Battery

For a long time chemists searched for eka-tantalum as an element with similar chemical properties as tantalum, making a discovery of protactinium nearly impossible.

In 1900, William Crookes isolated protactinium as an intensely radioactive material from uranium; Sony VGP-BPS10A Battery

however, he could not characterize it as a new chemical element and thus named it uranium-X.^[3][5] Crookes dissolved uranium nitrate in ether, the residual aqueous phase contains most of the 234
90Th and 234
91Pa. His method was still used in the 1950s to isolate 234
90Th and 234
91Pafrom uranium compounds.^[6] Protactinium was first identified in 1913, when Kasimir Fajans and Oswald Helmuth Göhring encountered the isotope ²³⁴Pa during their studies of the decay chains of uranium-238: 238Sony VGP-BPS11 Battery
92U ? 234
90Th ? 234
91Pa ? 234
92U. They named the new element brevium (from the Latin word, brevis, meaning brief or short) because of its short half-life, 6.7 hours for 234
91Pa.^{[7][8][9][10]} Sony VGP-BPL11 Battery

In 1918, two groups of scientists, led by Otto Hahn and Lise Meitner of Germany and Frederick Soddy and John Cranston of Great Britain, independently discovered another isotope of protactinium, ²³¹Pa having much longer half-life of about 32,000 years. Thus the name brevium was changed to protoactinium as the new element was part of the decay chain of uranium-235 before the actinium (from Greek: ?????? = protos meaning first, before). Sony VGP-BPL12 Battery

For ease of pronunciation, the name was shortened to protactinium by the IUPAC in 1949.^[11][12] The discovery of protactinium completed the last gap in the early versions of the periodic table, proposed by Mendeleev in 1869, and it brought to fame the involved scientists, particularly Meitner.^[13] Sony VGP-BPS12 Battery

Aristid von Grosse produced 2 milligrams of Pa₂O₅ in 1927,^[14] and in 1934 first isolated elemental protactinium from 0.1 milligrams of Pa₂O₅.^[15] He used two different procedures: in the first one, protactinium oxide was irradiated by 35 keV electrons in vacuum. In another method, called the van Arkel–de Boer process, the oxide was chemically converted to a halide(chloride, bromide or iodide) and then reduced in a vacuum with an electrically heated metallic filament:^[11][16] Sony VGP-BPL13 Battery

2 PaI₅ ? 2 Pa + 5 I₂

In 1961, the British Atomic Energy Authority (UKAEA) produced 125 grams of 99.9% pure protactinium by processing 60 tonnes of waste material in a 12-stage process, at a cost of about 500,000 USD.^[11] For many years, this was the world's only significant supply of protactinium, which was provided to various laboratories for scientific studies.^[3] Sony VGP-BPS13 Battery

Oak Ridge National Laboratory in the US is currently providing protactinium at a cost of about 280 USD/gram.^[17]

Occurrence

Protactinium is one of the rarest and most expensive naturally occurring elements. It is found in the form of two isotopes –²³¹Pa and ²³⁴Pa, with the isotope ²³⁴Pa occurring in two different energy states. Sony VGP-BPS13/B Battery

Nearly all natural protactinium is protactinium-231. It is an alpha emitter and is formed by the decay of uranium-235, whereas the beta radiating protactinium-234 is produced as a result of uranium-238 decay. Nearly all uranium-238 (99.8%) decays first to the ^234mPa isomer.^[18] Sony VGP-BPS13/S Battery

Sony VGP-BPS13/S Battery

Protactinium occurs in uraninite (pitchblende) at concentrations of about 0.3-3 parts ²³¹Pa per million parts (ppm) of ore.^[3]Whereas the usual content is closer to 0.3 ppm^[19] (e.g. in Jáchymov, Czech Republic^[20]), some ores from the Democratic Republic of the Congo have about 3 ppm.^[11] Sony VGP-BPS13A/B Battery

Protactinium is homogeneously dispersed in most natural materials and in water, but at much lower concentrations on the order of one part per trillion, that corresponds to the radioactivity of 0.1 picocuries (pCi)/g. There is about 500 times more protactinium in sandy soil particles than in water, even the water present in the same sample of soil. Much higher ratios of 2,000 and above are measured in loam soils and clays, such asbentonite.^[18][21] Sony VGP-BPS13A/S Battery

In nuclear reactors

Two major protactinium isotopes, ²³¹Pa and ²³³Pa are produced from thorium in nuclear reactors; both are undesirable and are usually removed, thereby adding complexity to the reactor design and operation. In particular, ²³²Th via (n,2n) reactions produces ²³¹Th which quickly (half-life 25.5 hours) decays to ²³¹Pa. Sony VGP-BPS13AS Battery

The last isotope, while not a transuranic waste, has a long half-life of 32,760 years and is a major contributor to the long term radiotoxicity of spent nuclear fuel.^[22]

Protactinium-233 is formed upon neutron capture by ²³²Th. It further either decays to uranium-233 or captures another neutron and converts into the non-fissile uranium-234.^{[23] 233}Sony VGP-BPS13B/B Battery

Pa has a relatively long half-life of 27 days and high cross section for neutron capture (the so-called "neutron poison"). Thus instead of rapidly decaying to the useful ²³³U, a significant fraction of²³³Pa converts to non-fissile isotopes and consumes neutrons, degrading the reactor efficiency. To avoid this, ²³³Pa is extracted from the active zone of thorium molten salt reactors, during their operation, so that it only decays to ²³³U. Sony VGP-BPS13B/Q Battery

This is achieved using several meters tall columns of molten bismuth with lithium dissolved in it. In a simplified scenario, lithium selectively reduces protactinium salts to protactinium metal which is then extracted from the molten-salt cycle, and bismuth is merely a carrier. It is chosen because of its low melting point (271 °C), low vapor pressure, good solubility for lithium and actinides, and immiscibility with molten halides.^[22] Sony VGP-BPS13B/S Battery

Preparation

Before the advent of nuclear reactors, protactinium was separated for scientific experiments from uranium ores. Nowadays, it is mostly produced as an intermediate product of nuclear fission in thorium high-temperature reactors: Sony VGP-BPS13Q Battery

Protactinium metal can be prepared by reduction of its fluoride with calcium fluoride,^[24] lithium or barium at a temperature of 1300–1400 °C.^[25][26]

Physical and chemical properties

Protactinium is an actinide which is positioned in the periodic table to the left of uranium and to the right of thorium, and many of its physical properties are intermediate between those two actinides. Sony VGP-BPS13S Battery

So, protactinium is more dense and rigid than thorium but is lighter than uranium, and its melting point is lower than that of thorium and higher than that of uranium. The thermal expansion, electrical and thermal conductivities of these three elements are comparable and are typical of "poor metals". The estimated shear modulus of protactinium is similar to that of titanium.^[27] Sony VGP-BPL7 Battery

Protactinium is a metal with silvery-gray luster that is preserved for some time in air.^[11][28] Protactinium easily reacts with oxygen, water vapor and acids, but not with alkali metals.^[3]

At room temperature, protactinium crystallizes in body-centered tetragonal structure which can be regarded as distorted body-centered cubic lattice; Sony VGP-BPS7 Battery

this structure does not change upon compression up to 53 GPa. The structure changes to face-centered cubic (fcc) upon cooling from high temperature, at about 1200 °C.^[24][29] The thermal expansion coefficient of the tetragonal phase between room temperature and 700 °C is 9.9×10^?6/°C.^[24] Sony VGP-BPL8 Battery

Protactinium is paramagnetic and no magnetic transitions are known for it at any temperature.^[30] It becomes superconductive at temperatures below 1.4 K.^[3][25]Protactinium tetrachloride is paramagnetic at room temperature but turns ferromagnetic upon cooling to 182 K.^[31] Sony VGP-BPL8A Battery

Protactinium exists in two major oxidation states, +4 and +5, both in solids and solutions, and the +3 and +2 states were observed in some solid phases. As the electron configuration of the neutral atom is 7s²6d¹5f², the +5 oxidation state corresponds to the low-energy (and thus favored) 5f⁰ configuration. Sony VGP-BPL8B Battery

Both +4 and +5 states easily form hydroxides in water with the predominant ions being Pa(OH)³⁺, Pa(OH)₂²⁺, Pa(OH)₃⁺ and Pa(OH)₄, all colorless.^[32] Other known protactinium ions include PaCl₂²⁺, PaSO₄²⁺, PaF³⁺, PaF₂²⁺, PaF₆^–, PaF₇^2– and PaF₈^3–.^[33][34]

Chemical compounds

Here a, b and c are lattice constants in picometers, No is space group number and Z is the number of formula units per unit cell; Sony VGP-BPS8 Battery

fccstands for the face-centered cubic symmetry. Density was not measured directly but calculated from the lattice parameters.

Oxides and oxygen-containing salts

Protactinium oxides are known for the metal oxidation states +2, +4 and +5. Sony VGP-BPS8A Battery

The most stable is white pentoxide Pa₂O₅, which can be produced by igniting protactinium(V) hydroxide in air at a temperature of 500 °C.^[42] Its crystal structure is cubic, and the chemical composition is often non-stoichiometric, described as PaO_2.25. Another phase of this oxide with orthorhombic symmetry has also been reported.^[26][43] Sony VGP-BPS8B Battery

The black dioxide PaO₂ is obtained from the pentoxide by reducing it at 1550 °C with hydrogen. It is not readily soluble in either dilute or concentrated nitric, hydrochloric or sulfuric acids, but easily dissolves in hydrofluoric acid.^[26] Sony VGP-BPL9 Battery

The dioxide can be converted back to pentoxide by heating in oxygen-containing atmosphere to 1100 °C.^[43] The monoxide PaO has only been observed as a thin coating on protactinium metal, but not in an isolated bulk form.^[26]

Protactinium forms mixed binary oxides with various metals. Sony VGP-BPS9 Battery

With alkali metals A, the crystals have a chemical formula APaO₃and perovskite structure, or A₃PaO₄ and distorted rock-salt structure, or A₇PaO₆ where oxygen atoms for a hexagonal close-packed lattice. In all these materials, protactinium ions are octahedrally coordinated.^[44][45] Sony VGP-BPS9/B Battery

The pentoxide Pa₂O₅ combines with rare-earth metal oxides R₂O₃ to form various nonstoichiometric mixed-oxides, also of perovskite structure.^[46]

Protactinium oxides are basic; they easily convert to hydroxides and can form various salts, such as sulfates, phosphates, nitrates, etc. Sony VGP-BPS9/S Battery

The nitrate is usually white but can be brown due to radiolytic decomposition. Heating the nitrate in air at 400 °C converts it to the white protactinium pentoxide.^[47] The polytrioxophosphate Pa(PO₃)₄ can be produced by reacting difluoride sulfate PaF₂SO₄with phosphoric acid (H₃PO₄) under inert gas atmosphere. Sony VGP-BPS9A Battery

Heating the product to about 900 °C eliminates the reaction by-products such as hydrofluoric acid, sulfur trioxide and phosphoric anhydride. Heating to higher temperatures in an inert atmosphere decomposes Pa(PO₃)₄ into the diphosphate PaP₂O₇, which is analogous to diphosphates of other actinides. Sony VGP-BPS9A/B Battery

In the diphosphate, the PO₃ groups form pyramids of C_2v symmetry. Heating PaP₂O₇ in air to 1400 °C decomposes it into the pentoxides of phosphorus and protactinium.^[40]

Halides

Protactinium(V) fluoride forms white crystals where protactinium ions are arranged in pentagonal bipyramids and coordinated by 7 other ions. Sony VGP-BPS9A/S Battery

The coordination is the same in protactinium(V) chloride, but the color is yellow. The coordination changes to octahedral in the brown protactinium(V) bromide and is unknown for protactinium(V) iodide. The protactinium coordination in all its tetrahalides is 8, but the arrangement is square antiprismatic in protactinium(IV) fluoride and dodecahedral in the chloride and bromide. Sony VGP-BPS9B Battery

Sony VGP-BPX11 Battery

Brown-colored protactinium(III) iodide has been reported where protactinium ions are 8-coordinated in a bicapped trigonal prismatic arrangement.^[48]

Protactinium(V) fluoride and protactinium(V) chloride have a polymeric structure of monoclinic symmetry. Sony VGP-BPL18 Battery

There, within one polymeric chain, all the halide atoms lie in one graphite-like plane and form planar pentagons around the protactinium ions. The coordination 7 of protactinium originates from the 5 halide atoms and two bonds to protactinium atoms belonging to the nearby chains. Sony VGP-BPS18 Battery

These compounds easily hydrolyze in water.^[49] The pentachloride melts at 300 °C and sublimates at even lower temperatures.

Protactinium(V) fluoride can be prepared by reacting protactinium oxide with either bromine pentafluoride or bromine trifluoride at about 600 °C, and protactinium(IV) fluoride is obtained from the oxide and a mixture of hydrogen and hydrogen fluoride at 600 °C; Sony VGP-BPL20 Battery

a large excess of hydrogen is required to remove atmospheric oxygen leaks into the reaction.^[26]

Protactinium(V) chloride is prepared by reacting protactinium oxide with carbon tetrachloride at temperature of 200–300 °C.^[26]The by-products (such as PaOCl₃) are removed by fractional sublimation.^[38] Sony VGP-BPS20/B Battery

Reduction of protactinium(V) chloride with hydrogen at about 800 °C yields protactinium(IV) chloride – a yellow-green solid which sublimes in vacuum at 400 °C; it can also be obtained directly from protactinium dioxide by treating it with carbon tetrachloride at 400 °C.^[26] Sony VGP-BPS20/S Battery

Protactinium bromides are produced by the action of aluminum bromide, hydrogen bromide, carbon tetrabromide or a mixture of hydrogen bromide and thionyl bromide on protactinium oxide. An alternative reaction is between protactinium pentachloride and hydrogen bromide or thionyl bromide.^[26] Sony VGP-BPL21 Battery

Protactinium(V) bromide has two similar monoclinic forms, one is obtained by sublimation at 400–410 °C and another by sublimation at slightly lower temperature of 390–400 °C.^[37][39]

Protactinium iodides result from the oxides and aluminum iodide or ammonium iodide heated to 600 °C.^[26] Sony VGP-BPS21 Battery

Protactinium(III) iodide was obtained by heating protactinium(V) iodide in vacuum.^[49] As with oxides, protactinium forms mixed halides with alkali metals. Among those, most remarkable is Na₃PaF₈ where protactinium ion is symmetrically surrounded by 8 F^– ions which form a nearly perfect cube.^[33] Sony VGP-BPS21/S Battery

More complex protactinium fluorides are also known such as Pa₂F₉^[49] and ternary fluorides of the types MPaF₆ (M = Li, Na, K, Rb, Cs or NH₄), M₂PaF₇ (M = K, Rb, Cs or NH₄) and M₃PaF₈ (M = Li, Na, Rb, Cs), all being white crystalline solids. The MPaF₆ formula can be represented as a combination of MF and PaF₅. Sony VGP-BPS21A Battery

These compounds can be obtained by evaporating a hydrofluoric acid solution containing these both complexes. For the small alkali cations like Na, the crystal structure is tetragonal, whereas it lowers to orthorphombic for larger cations K⁺, Rb⁺, Cs⁺ or NH₄⁺. A similar variation was observed for the M₂PaF₇ fluorides, namely the crystal symmetry was dependent on the cation and differed for Cs₂PaF₇ and M₂PaF₇ (M = K, Rb or NH₄).^[34] Sony VGP-BPS21A/B Battery

Other inorganic compounds

Oxyhalides and oxysulfides of protactinium are known. PaOBr₃ has a monoclinic structure composed of double-chain units where protactinium has coordination 7 and is arranged into pentagonal bipyramids. Sony VGP-BPS21B Battery

The chains are interconnected through oxygen and bromine atoms, and each oxygen atom is related to three Pa atoms.^[37] PaOS is a light-yellow non-volatile solid with a cubic crystal lattice isostructural to that of other actinide oxysulfides. It is obtained by reacting protactinium(V) chloride with a mixture of hydrogen sulfide and carbon disulfide at 900 °C.^[26] Sony VGP-BPL22 Battery

In hydrides and nitrides, protactinium has a low oxidation state of about +3. The hydride is obtained by direct action of hydrogen on the metal at 250 °C, and the nitride is a product of ammonia and protactinium tetrachloride or pentachloride. This bright yellow solid is stable to heating to 800 °C in vacuum. Sony VGP-BPS22 Battery

Protactinium carbide PaC is formed by reduction of protactinium tetrafluoride with barium in a carbon crucible at a temperature of about 1400 °C.^[26] Protactinium forms borohydrides which include Pa(BH₄)₄. It has an unusual polymeric structure with helical chains where the protactinium atom has coordination number of 12 and is surrounded by six BH₄^– ions.^[50] Sony VGP-BPS22/A Battery

Organometallic compounds

Protactinium(IV) forms a tetrahedral complex tetrakis(cyclopentadienyl)protactinium(IV) (or Pa(C₅H₅)₄) with four cyclopentadienyl rings, which can be synthesized by reacting protactinium(IV) chloride with molten Be(C₅H₅)₂. One ring can be substituted with a halide atom.^[51] Sony VGP-BPS22A Battery

Another organometallic complex is golden-yellow bis(?-cyclooctatetraene) protactinium, Pa(C₈H₈)₂, which is analogous in structure touranocene. There, the metal atom is sandwiched between two cyclooctatetraeneligands. Similar to uranocene, it can be prepared by reacting protactinium tetrachloride with dipotassium cyclooctatetraenide, K₂C₈H₈, in tetrahydrofuran.^[41] Sony VGP-BPL23 Battery

Twenty-nine radioisotopes of protactinium have been discovered, the most stable being ²³¹Pa with a half-life of 32,760 years, ²³³Pa with a half-life of 27 days, and ²³⁰Pa with a half-life of 17.4 days. All of the remaining isotopes have half-lives shorter than 1.6 days, and the majority of these have half-lives less than 1.8 seconds. Sony VGP-BPS23 Battery

Protactinium also has two nuclear isomers, ^217mPa (half-life 1.2 milliseconds) and ^234mPa (half-life 1.17 minutes).^[52]

The primary decay mode for isotopes of protactinium lighter than (and including) the most stable isotope ²³¹Pa (i.e., ²¹²Pa to ²³¹Pa) is alpha decay and the primary mode for the heavier isotopes (i.e., ²³²Pa to ²⁴⁰Pa) is beta decay. Sony VGP-BPS23/B Battery

The primary decay products of isotopes of protactinium lighter than (and including) ²³¹Pa areactinium isotopes and the primary decay products for the heavier isotopes of protactinium are uranium isotopes.^[52]

Applications

Although protactinium is located in the periodic table between uranium and thorium, Sony VGP-BPS23/D Battery

which both have numerous applications, owing to its scarcity, high radioactivity and high toxicity, there are currently no uses for protactinium outside of scientific research.^[18]

Protactinium-231 arises from the decay of uranium-235 formed in nuclear reactors, and by the reaction ²³²Th + n ? ²³¹Th + 2n and subsequent beta decay. Sony VGP-BPS23/G Battery

It may support a nuclear chain reaction, which could in principle be used to build nuclear weapons. The physicist Walter Seifritz once estimated the associated critical mass as 750±180 kg,^[53] but this possibility (of a chain reaction) has been ruled out by other nuclear physicists since then.^[54] Sony VGP-BPS23/P Battery

Sony VGP-BPS23/W Battery

With the advent of highly sensitive mass spectrometers, an application of ²³¹Pa as a tracer in geology and paleoceanography has become possible. So, the ratio of protactinium-231 to thorium-230 is used for radiometric dating of sediments which are up to 175,000 years old and in modeling of the formation of minerals.^[19] Sony Limited Edition 007 Battery

In particular, its evaluation in oceanic sediments allowed to reconstruct the movements of North Atlantic water bodies during the last melting of Ice Age glaciers.^[55]Some of the protactinium-related dating variations rely on the analysis of the relative concentrations for several long-living members of the uranium decay chain – uranium, thorium and protactinium, for example. Sony VAIO VGC-LB15 Battery

These elements have 6, 5 and 4 f-electrons in the outer shell and thus favor +6, +5 and +4 oxidation states, respectively, and show different physical and chemical properties. So, thorium and protactinium, but not uranium compounds are poorly soluble in aqueous solutions, and precipitate into sediments; the precipitation rate is faster for thorium than for protactinium. Sony VGN-AR Series Battery

Besides, the concentration analysis for both protactinium-231 (half-life 32,750 years) and thorium-230 (half-life 75,380 years) allows to improve the accuracy compared to when only one isotope is measured; this double-isotope method is also weakly sensitive to inhomogeneities in the spatial distribution of the isotopes and to variations in their precipitation rate.^[19][56] Sony VGN-CR Series Battery

Precautions

Protactinium is both toxic and highly radioactive and thus all manipulations with it are performed in a sealed glove box. Its major isotope ²³¹Pa has a specific activity of 0.048 Ci/gram and primarily emits alpha-particles of the energy 5 MeV, which can be stopped by a thin layer of any material. Sony VIAO VGN-G Series Battery

However, it slowly decays, with the half-life of 32,760 years, into ²²⁷Ac, which has a specific activity of 74 Ci/gram, emits both alpha and beta radiation, and has a much shorter half-life of 22 years. ²²⁷Ac, in turn, decays into lighter isotopes with even shorter half-lives and much greater specific activities (SA), as summarized in the table below.^[18] Sony VIAO VGN-G118 Battery

As protactinium is present in small amounts in most natural products and materials, it is ingested with food or water and inhaled with air. Only about 0.05% of ingested protactinium is absorbed into the blood and the remainder is excreted. From the blood, about 40% of the protactinium deposits in the bones, about 15% goes to the liver, 2% to the kidneys, and the rest leaves the body. Sony VIAO VGN-G118CN/B Battery

The biological half-life of protactinium is about 50 years in the bones, whereas in other organs the kinetics has a fast and slow component. So in the liver 70% of protactinium have a half-life of 10 days and 30% remain for 60 days. The corresponding values for kidneys are 20% (10 days) and 80% (60 days). Sony VIAO VGN-G118CN/T Battery

In all these organs, protactinium promotes cancer via its radioactivity.^[18][47] The maximum safe dose of Pa in the human body is 0.03 µCi that corresponds to 0.5 micrograms of ²³¹Pa. This isotope is 2.5×10⁸ times more toxic than hydrocyanic acid.^[57] The maximum allowed concentrations of ²³¹Pa in the air is 3×10^?4 Bq/m³. Sony VIAO VGN-G218 Battery

Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. The uranium nucleus binds between 141 and 146 neutrons, establishing six isotopes (U-233 through U-238), Sony VGN-TZ121 Battery

the most common of which are uranium-238 (146 neutrons) and uranium-235 (143 neutrons). All isotopes are unstable and uranium is weakly radioactive. Uranium has the second highest atomic weight of the naturally occurring elements, lighter only than plutonium-244.^[3] Sony VGN-TZ13 Battery

Its density is about 70% higher than that of lead, but not as dense as goldor tungsten. It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite. Sony VGN-TZ131 Battery

Sony VGN-TZ132N Battery

In nature, uranium is found as uranium-238 (99.2742%), uranium-235 (0.7204%), and a very small amount of uranium-234(0.0054%). Uranium decays slowly by emitting an alpha particle. The half-life of uranium-238 is about 4.47 billion years and that of uranium-235 is 704 million years,^[4] making them useful in dating the age of the Earth. Sony VGN-TZ132/N Battery

Many contemporary uses of uranium exploit its unique nuclear properties. Uranium-235 has the distinction of being the only naturally occurring fissile isotope. Uranium-238 is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor. Sony VGN-TZ17N Battery

Another fissile isotope, uranium-233, can be produced from natural thorium and is also important in nuclear technology. While uranium-238 has a small probability for spontaneous fission or even induced fission with fast neutrons, uranium-235 and to a lesser degree uranium-233 have a much higher fission cross-section for slow neutrons. Sony VGN-TZ16N Battery

In sufficient concentration, these isotopes maintain a sustained nuclear chain reaction. This generates the heat in nuclear power reactors, and produces the fissile material for nuclear weapons.Depleted uranium (²³⁸U) is used in kinetic energy penetrators and armor plating.^[5]

Uranium is used as a colorant in uranium glass, producing orange-red to lemon yellow hues. Sony VGN-TZ18N Battery

It was also used for tinting and shading in early photography. The 1789 discovery of uranium in the mineral pitchblende is credited to Martin Heinrich Klaproth, who named the new element after the planet Uranus. Eugène-Melchior Péligot was the first person to isolate the metal and its radioactive properties were discovered in 1896 by Antoine Becquerel. Sony VAIO VGN-AR47G/E1 Battery

Research by Enrico Fermi and others starting in 1934 led to its use as a fuel in the nuclear power industry and in Little Boy, the first nuclear weapon used in war. An ensuing arms race during the Cold Warbetween the United States and the Soviet Union produced tens of thousands of nuclear weapons that used uranium metal and uranium-derived plutonium-239. Sony VAIO VGN-AR520E Battery

The security of those weapons and their fissile material following the breakup of the Soviet Union in 1991 is an ongoing concern for public health and safety.^[6]See Nuclear proliferation.

Characteristics

When refined, uranium is a silvery white, weakly radioactive metal, which is harder than most elements. Sony VAIO VGN-AR53DB Battery

It is malleable, ductile, slightly paramagnetic, strongly electropositive and is a poorelectrical conductor.^[7][8] Uranium metal has very high density, being approximately 70% denser than lead, but slightly less dense than gold.

Uranium metal reacts with almost all nonmetallic elements and their compounds, with reactivity increasing with temperature.^[9] Sony VAIO VGN-AR54DB Battery

Hydrochloric and nitric acids dissolve uranium, but nonoxidizing acids attack the element very slowly.^[7] When finely divided, it can react with cold water; in air, uranium metal becomes coated with a dark layer of uranium oxide.^[8] Uranium in ores is extracted chemically and converted into uranium dioxide or other chemical forms usable in industry. Sony VAIO VGN-AR550E Battery

Uranium-235 was the first isotope that was found to be fissile. Other naturally occurring isotopes are fissionable, but not fissile. Upon bombardment with slow neutrons, its uranium-235isotope will most of the time divide into two smaller nuclei, releasing nuclear binding energyand more neutrons. Sony VAIO VGN-AR55DB Battery

If too many of these neutrons are absorbed by other uranium-235 nuclei, anuclear chain reaction occurs that results in a burst of heat or (in special circumstances) an explosion. In a nuclear reactor, such a chain reaction is slowed and controlled by a neutron poison, absorbing some of the free neutrons. Sony VAIO VGN-AR630E Battery

Such neutron absorbent materials are often part of reactor control rods (seenuclear reactor physics for a description of this process of reactor control).

As little as 15 lb (7 kg) of uranium-235 can be used to make an atomic bomb.^[10] The first nuclear bomb used in war, Little Boy, Sony VAIO VGN-AR64DB Battery

relied on uranium fission, while the very first nuclear explosive (The gadget) and the bomb that destroyed Nagasaki (Fat Man) were plutonium bombs.

Uranium metal has three allotropic forms:^[11]

• ? (orthorhombic) stable up to 660 °C


• ? (tetragonal) stable from 660 °C to 760 °C

? (body-centered cubic) from 760 °C to melting point—this is the most malleable and ductile state. Sony VAIO VGN-AR65DB Battery

Military

The major application of uranium in the military sector is in high-density penetrators. This ammunition consists of depleted uranium(DU) alloyed with 1–2% other elements. At high impact speed, the density, hardness, and pyrophoricity of the projectile enable destruction of heavily armored targets. Sony VAIO VGN-AR660U Battery

Tank armor and other removable vehicle armorare also hardened with depleted uranium plates. The use of DU became politically and environmentally contentious after the use of DU munitions by the US, UK and other countries during wars in the Persian Gulf and the Balkans raised questions of uranium compounds left in the soil (see Gulf War Syndrome).^[10] Sony VAIO VGN-AR690U Battery

Depleted uranium is also used as a shielding material in some containers used to store and transport radioactive materials. While the metal itself is radioactive, its high density makes it more effective than lead in halting radiation from strong sources such as radium.^[7] Other uses of DU include counterweights for aircraft control surfaces, as ballast for missile re-entry vehicles and as a shielding material.^[8] Sony VAIO VGN-AR71ZU Battery

Due to its high density, this material is found in inertial guidance systems and in gyroscopic compasses.^[8] DU is preferred over similarly dense metals due to its ability to be easily machined and cast as well as its relatively low cost.^[12] Counter to popular belief, the main risk of exposure to DU is chemical poisoning by uranium oxide rather than radioactivity (uranium being only a weak alpha emitter). Sony VAIO VGN-AR730E/B Battery

During the later stages of World War II, the entire Cold War, and to a lesser extent afterwards, uranium-235 has been used as the fissile explosive material to produce nuclear weapons. Initially, two major types of fission bombs were built: Sony VAIO VGN-AR73DB Battery

a relatively simple device that uses uranium-235 and a more complicated mechanism that uses plutonium-239 derived from uranium-238. Later, a much more complicated and far more powerful type of fission/fusion bomb (thermonuclear weapon) was built, that uses a plutonium-based device to cause a mixture of tritium and deuterium to undergo nuclear fusion. Sony VAIO VGN-AR74DB Battery

Such bombs are jacketed in a non-fissile (unenriched) uranium case, and they derive more than half their power from the fission of this material by fast neutrons from the nuclear fusion process.^[13]

Civilian

The most visible civilian use of uranium is as the thermal power source used in nuclear power plants. Sony VAIO VGN-AR75UDB Battery

The main use of uranium in the civilian sector is to fuel nuclear power plants. One kilogram of uranium-235 can theoretically produce about 80 terajoules of energy (8×10¹³ joules), assuming complete fission; as much energy as 3000 tonnes of coal.^[5]

Commercial nuclear power plants use fuel that is typically enriched to around 3% uranium-235.^[5] Sony VAIO VGN-AR790U/B Battery

The CANDU and Magnox designs are the only commercial reactors capable of using unenriched uranium fuel. Fuel used for United States Navy reactors is typically highly enriched in uranium-235 (the exact values are classified). In a breeder reactor, uranium-238 can also be converted intoplutonium through the following reaction:^{[8] 238}U (n, gamma) ? ²³⁹U -(beta) ? ²³⁹Np -(beta) ? ²³⁹Pu. Sony VAIO VGN-AR820E Battery

Before the discovery of radioactivity, uranium was primarily used in small amounts for yellow glass and pottery glazes, such as uranium glass and in Fiestaware.

The discovery and isolation of radium in uranium ore (pitchblende) by Marie Curie sparked the development of uranium mining to extract the radium, which was used to make glow-in-the-dark paints for clock and aircraft dials.^[14] Sony VAIO VGN-AR830E Battery

This left a prodigious quantity of uranium as a waste product, since it takes three metric tons of uranium to extract one gram of radium. This waste product was diverted to the glazing industry, making uranium glazes very inexpensive and abundant. Besides the pottery glazes, uranium tileglazes accounted for the bulk of the use, including common bathroom and kitchen tiles which can be produced in green, yellow, mauve, black, blue, red and other colors. Sony VAIO VGN-AR83S Battery

Uranium was also used in photographic chemicals (especially uranium nitrate as a toner),^[8] in lamp filaments, to improve the appearance of dentures, and in the leather and wood industries for stains and dyes. Uranium salts are mordants of silk or wool. Uranyl acetate and uranyl formate are used as electron-dense "stains" in transmission electron microscopy, Sony VAIO VGN-AR83US Battery

to increase the contrast of biological specimens in ultrathin sections and in negative staining of viruses, isolated cell organelles and macromolecules.

The discovery of the radioactivity of uranium ushered in additional scientific and practical uses of the element. Sony VAIO VGN-AR84S Battery

The long half-life of the isotope uranium-238 (4.51×10⁹ years) makes it well-suited for use in estimating the age of the earliest igneous rocks and for other types of radiometric dating, including uranium-thorium dating and uranium-lead dating. Uranium metal is used for X-raytargets in the making of high-energy X-rays.^[8] Sony VAIO VGN-AR84US Battery

Prehistoric naturally occurring fission

In 1972 French physicist Francis Perrin discovered fifteen ancient and no longer active natural nuclear fission reactors in three separate ore deposits at the Oklomine in Gabon, West Africa, collectively known as the Oklo Fossil Reactors. Sony VAIO VGN-AR85S Battery

The ore deposit is 1.7 billion years old; then, uranium-235 constituted about three percent of the total uranium on Earth.^[15] This is high enough to permit a sustained nuclear fission chain reaction to occur, provided other supporting conditions exist. Sony VAIO VGN-AR85US Battery

The capacity of the surrounding sediment to contain the nuclear waste products has been cited by the U.S. federal government as supporting evidence for the feasibility to store spent nuclear fuel at the Yucca Mountain nuclear waste repository.^[15]

Pre-discovery use

The use of uranium in its natural oxide form dates back to at least the year 79 CE, when it was used to add a yellow color to ceramicglazes.^[8] Sony VAIO VGN-AR870EA Battery

Yellow glass with 1% uranium oxide was found in a Roman villa on Cape Posillipo in the Bay of Naples, Italy by R. T. Gunther of the University of Oxford in 1912.^[16] Starting in the lateMiddle Ages, pitchblende was extracted from the Habsburg silver mines in Joachimsthal, Bohemia (now Jáchymov in the Czech Republic) and was used as a coloring agent in the local glassmakingindustry.^[17] Sony VAIO VGN-AR890U Battery

In the early 19th century, the world's only known sources of uranium ore were these mines.

Discovery

The discovery of the element is credited to the German chemist Martin Heinrich Klaproth. While he was working in his experimental laboratory in Berlin in 1789, Klaproth was able to precipitate a yellow compound (likely sodium diuranate) by dissolvingpitchblendein nitric acid and neutralizing the solution with sodium hydroxide.^[17] Sony VAIO VGN-AR93S Battery

Klaproth assumed the yellow substance was the oxide of a yet-undiscovered element and heated it with charcoal to obtain a black powder, which he thought was the newly discovered metal itself (in fact, that powder was an oxide of uranium).^[17][18] He named the newly discovered element after the planet Uranus, Sony VAIO VGN-AR93US Battery

which had been discovered eight years earlier by William Herschel (who had named the planet after the primordialGreek god of the sky).^[19]

In 1841, Eugène-Melchior Péligot, Professor of Analytical Chemistry at the Conservatoire National des Arts et Métiers (Central School of Arts and Manufactures) in Paris, isolated the first sample of uranium metal by heating uranium tetrachloridewithpotassium.^[17][20] Sony VAIO VGN-AR94S Battery

Uranium was not seen as being particularly dangerous during much of the 19th century, leading to the development of various uses for the element. One such use for the oxide was the aforementioned but no longer secret coloring of pottery and glass.

Antoine Henri Becquerel discovered radioactivity by using uranium in 1896.^[9] Sony VAIO VGN-AR94US Battery

Becquerel made the discovery in Paris by leaving a sample of a uranium salt, K₂UO₂(SO₄)₂ (potassium uranyl sulfate), on top of an unexposed photographic plate in a drawer and noting that the plate had become 'fogged'.^[21] He determined that a form of invisible light or rays emitted by uranium had exposed the plate. Sony VAIO VGN-AR95S Battery

Fission research

A team led by Enrico Fermi in 1934 observed that bombarding uranium with neutrons produces the emission of beta rays (electronsorpositrons from the elements produced; see beta particle).^[22] Sony VAIO VGN-AR95US Battery



The fission products were at first mistaken for new elements of atomic numbers 93 and 94, which the Dean of the Faculty of Rome, Orso Mario Corbino, christened ausonium and hesperium, respectively.^{[23][24][25][26]} The experiments leading to the discovery of uranium's ability to fission (break apart) into lighter elements and release binding energy were conducted by Otto Hahn and Fritz Strassmann^[22] in Hahn's laboratory in Berlin. Sony VAIO VGN-AW110J/H Battery

Lise Meitner and her nephew, physicist Otto Robert Frisch, published the physical explanation in February 1939 and named the process 'nuclear fission'.^[27] Soon after, Fermi hypothesized that the fission of uranium might release enough neutrons to sustain a fission reaction. Sony VAIO VGN-AW11M/H Battery

Confirmation of this hypothesis came in 1939, and later work found that on average about 2.5 neutrons are released by each fission of the rare uranium isotope uranium-235.^[22] Further work found that the far more common uranium-238 isotope can be transmuted into plutonium, which, like uranium-235, is also fissionable by thermal neutrons. Sony VAIO VGN-AW11S/B Battery

These discoveries led numerous countries to begin working on the development of nuclear weapons and nuclear power.

On 2 December 1942, as part of the Manhattan Project, another team led by Enrico Fermi was able to initiate the first artificial self-sustained nuclear chain reaction, Chicago Pile-1. Sony VAIO VGN-AW11XU/Q Battery

Working in a lab below the stands of Stagg Field at the University of Chicago, the team created the conditions needed for such a reaction by piling together 400 tons (360 tonnes) of graphite, 58 tons (53 tonnes) of uranium oxide, and six tons (five and a half tonnes) of uranium metal.^[22] Sony VAIO VGN-AW11Z/B Battery

Bombs

Two major types of atomic bombs were developed by the United States during World War II: a uranium-based device (codenamed "Little Boy") whose fissile material was highly enriched uranium, and a plutonium-based device (see Trinity test and "Fat Man") whose plutonium was derived from uranium-238. Sony VAIO VGN-AW120J/H Battery

The uranium-based Little Boy device became the first nuclear weapon used in war when it was detonated over the Japanese city of Hiroshima on 6 August 1945. Exploding with a yield equivalent to 12,500 tonnes of TNT, the blast and thermal wave of the bomb destroyed nearly 50,000 buildings and killed approximately 75,000 people (see Atomic bombings of Hiroshima and Nagasaki).^[21Sony VAIO VGN-AW150Y/H Battery

^] Initially it was believed that uranium was relatively rare, and that nuclear proliferationcould be avoided by simply buying up all known uranium stocks, but within a decade large deposits of it were discovered in many places around the world.^[28]

Reactors

The X-10 Graphite Reactor at Oak Ridge National Laboratory (ORNL) in Oak Ridge, Sony VAIO VGN-AW160J/Q Battery

Tennessee, formerly known as the Clinton Pile and X-10 Pile, was the world's second artificial nuclear reactor (after Enrico Fermi's Chicago Pile) and was the first reactor designed and built for continuous operation. The Experimental Breeder Reactor I at the Idaho National Laboratory (INL) near Arco, Idahobecame the first nuclear reactor to create electricity on 20 December 1951. Sony VAIO VGN-AW170Y/Q Battery

Sony VAIO VGN-AW180Y/Q Battery

Initially, four 150-watt light bulbs were lit by the reactor, but improvements eventually enabled it to power the whole facility (later, the town of Arco became the first in the world to have all its electricity come from nuclear power).^[29] The world's first commercial scale nuclear power station, Obninsk in the Soviet Union, began generation with its reactor AM-1 on 27 June 1954. Sony VAIO VGN-AW190JAH Battery

Other early nuclear power plants were Calder Hall in England which began generation on 17 October 1956^[30]and the Shippingport Atomic Power Station in Pennsylvania which began on 26 May 1958. Nuclear power was used for the first time for propulsion by a submarine, the USS Nautilus, in 1954.^[22] Sony VAIO VGN-AW190NAB Battery

Contamination and the Cold War legacy

Above-ground nuclear tests by the Soviet Union and the United States in the 1950s and early 1960s and by France into the 1970s and 1980s^[12] spread a significant amount of fallout from uranium daughter isotopes around the world.^[31] Additional fallout and pollution occurred from several nuclear accidents.^[32][33] Sony VAIO VGN-AW190NBB Battery

Uranium miners have a higher incidence of cancer. An excess risk of lung cancer among Navajo uranium miners, for example, has been documented and linked to their occupation.^[34] The Radiation Exposure Compensation Act, a 1990 law, required $100,000 in "compassion payments" to uranium miners diagnosed with cancer or other respiratory ailments.^[35] Sony VAIO VGN-AW190NCB Battery

During the Cold War between the Soviet Union and the United States, huge stockpiles of uranium were amassed and tens of thousands of nuclear weapons were created using enriched uranium and plutonium made from uranium. Since the break-up of the Soviet Unionin 1991, Sony VAIO VGN-AW190YAB Battery

an estimated 600 tons (540 tonnes) of highly enriched weapons grade uranium (enough to make 40,000 nuclear warheads) have been stored in often inadequately guarded facilities in the Russian Federation and several other former Soviet states.^[10] Police in Asia, Europe, and South America on at least 16 occasions from 1993 to 2005 have intercepted shipments of smuggled bomb-grade uranium or plutonium, Sony VAIO VGN-AW190YBB Battery

most of which was from ex-Soviet sources.^[10] From 1993 to 2005 the Material Protection, Control, and Accounting Program, operated by the federal government of the United States, spent approximately US $550 million to help safeguard uranium and plutonium stockpiles in Russia.^[10] Sony VAIO VGN-AW190YCB Battery

This money was used for improvements and security enhancements at research and storage facilities. Scientific American reported in February 2006 that some of the facilities security consisted of chain link fences which were in severe states of disrepair. According to an interview from the article, one facility had been storing samples of enriched (weapons grade) uranium in a broom closet before the improvement project; Sony VAIO VGN-AW190YDB Battery

another had been keeping track of its stock of nuclear warheads using index cards kept in a shoe box.^[36]

Biotic and abiotic

Uranium is a naturally occurring element that can be found in low levels within all rock, soil, and water. Uranium is also the highest-numbered element to be found naturally in significant quantities on earth and is always found combined with other elements.^[8] Sony VAIO VGN-AW220J/B Battery

Along with all elements having atomic weights higher than that of iron, it is only naturally formed in supernovae.^[37]The decay of uranium, thorium, and potassium-40 in the Earth's mantle is thought to be the main source of heat^[38][39] that keeps the outer coreliquid and drives mantle convection, which in turn drives plate tectonics. Sony VAIO VGN-AW230J/H Battery

Uranium's average concentration in the Earth's crust is (depending on the reference) 2 to 4 parts per million,^[7][12] or about 40 times as abundant as silver.^[9] The Earth's crust from the surface to 25 km (15 mi) down is calculated to contain 10¹⁷ kg (2×10¹⁷ lb) of uranium while the oceans may contain 10¹³ kg (2×10¹³ lb).^[7] Sony VAIO VGN-AW235J/B Battery

The concentration of uranium in soil ranges from 0.7 to 11 parts per million (up to 15 parts per million in farmland soil due to use of phosphate fertilizers), and its concentration in sea water is 3 parts per billion.^[12]

Uranium is more plentiful than antimony, tin, cadmium, mercury, or silver, and it is about as abundant as arsenicormolybdenum.^[8][12] Sony VAIO VGN-AW290JFQ Battery

Uranium is found in hundreds of minerals including uraninite (the most common uranium ore), carnotite, autunite,uranophane, torbernite, and coffinite.^[8] Significant concentrations of uranium occur in some substances such as phosphate rock deposits, and minerals such as lignite, and monazite sands in uranium-rich ores^[8] (it is recovered commercially from sources with as little as 0.1% uranium^[9]). Sony VAIO VGN-AW41JF Battery

Some bacteria such as S. putrefaciens and G. metallireducens have been shown to reduce U(VI) to U(IV).^[40]

Some organisms, such as the lichen Trapelia involuta or microorganisms such as the bacterium Citrobacter, can absorb concentrations of uranium that are up to 300 times higher than in their environment.^[41] Sony VAIO VGN-AW41JF/H Battery

Citrobacter species absorb uranyl ions when given glycerol phosphate (or other similar organic phosphates). After one day, one gram of bacteria can encrust themselves with nine grams of uranyl phosphate crystals; this creates the possibility that these organisms could be used in bioremediationtodecontaminate uranium-polluted water.^[17][42] Sony VAIO VGN-AW41MF Battery

In nature, uranium(VI) forms highly soluble carbonate complexes at alkaline pH. This leads to an increase in mobility and availability of uranium to groundwater and soil from nuclear wastes which leads to health hazards. However, it is difficult to precipitate uranium as phosphate in the presence of excess carbonate at alkaline pH. Sony VAIO VGN-AW41MF/H Battery

A Sphingomonas sp. strain BSAR-1 has been found to express a high activity alkaline phosphatase (PhoK) that has been applied for bioprecipitation of uranium as uranyl phosphate species from alkaline solutions. The precipitation ability was enhanced by overexpressing PhoK protein in E. coli.^[43] Sony VAIO VGN-AW41XH Battery

Plants absorb some uranium from soil. Dry weight concentrations of uranium in plants range from 5 to 60 parts per billion, and ash from burnt wood can have concentrations up to 4 parts per million.^[17] Dry weight concentrations of uranium in food plants are typically lower with one to two micrograms per day ingested through the food people eat.^[17] Sony VAIO VGN-AW41XH/Q Battery

Production and mining

The worldwide production of uranium in 2009 amounted to 50,572 tonnes, of which 27.3% was mined in Kazakhstan. Other important uranium mining countries are Canada (20.1%), Australia (15.7%), Namibia (9.1%), Russia (7.0%), and Niger (6.4%).^[44] Sony VAIO VGN-AW41ZF Battery

Uranium ore is mined in several ways: by open pit, underground, in-situ leaching, and borehole mining (see uranium mining).^[5]Low-grade uranium ore mined typically contains 0.01 to 0.25% uranium oxides. Extensive measures must be employed to extract the metal from its ore.^[45] Sony VAIO VGN-AW41ZF/B Battery

High-grade ores found in Athabasca Basin deposits in Saskatchewan, Canada can contain up to 23% uranium oxides on average.^[46] Uranium ore is crushed and rendered into a fine powder and then leached with either an acid or alkali. Theleachate is subjected to one of several sequences of precipitation, solvent extraction, and ion exchange. Sony VAIO VGN-AW50DB/H Battery

The resulting mixture, called yellowcake, contains at least 75% uranium oxides. Yellowcake is then calcined to remove impurities from the milling process before refining and conversion.^[47]

Commercial-grade uranium can be produced through the reduction of uranium halides with alkali or alkaline earth metals.^[8Sony VAIO VGN-AW51JGB Battery

^]Uranium metal can also be prepared through electrolysis of KU₅ or UF₄, dissolved in molten calcium chloride (CaCl₂) and sodium chloride(NaCl) solution.^[8] Very pure uranium is produced through the thermal decomposition of uranium halides on a hot filament.^[8] Sony VAIO VGN-AW52JGB Battery

Resources and reserves

It is estimated that 5.5 million tonnes of uranium ore reserves are economically viable at US$59/lb,^[48] while 35 million tonnes are classed as mineral resources (reasonable prospects for eventual economic extraction).^[49] Sony VAIO VGN-AW53FB Battery

An additional 4.6 billion tonnes of uranium are estimated to be in sea water (Japanese scientists in the 1980s showed that extraction of uranium from sea water usingion exchangers was technically feasible).^[50][51] There have been experiments to extract uranium from sea water,^[52] but the yield has been low due to the carbonate present in the water. Sony VAIO VGN-AW70B/Q Battery

Exploration for uranium is increasing with US$200 million being spent world wide in 2005, a 54% increase on the previous year,^[49]thanks to growing prices on uranium market. This trend continued through 2006, when expenditure on exploration rocketed to over $774 million, an increase of over 250% compared to 2004. Sony VAIO VGN-AW71JB Battery

The OECD Nuclear Energy Agency said exploration figures for 2007 would likely match those for 2006.^[48]

Australia has 31% of the world's uranium ore reserves^[53] and the world's largest single uranium deposit, located at the Olympic DamMine in South Australia.^[54] Sony VAIO VGN-AW72JB Battery

Some nuclear fuel comes from nuclear weapons being dismantled,^[55] such as from the Megatons to Megawatts Program.

Supply

In 2005, seventeen countries produced concentrated uranium oxides, with Canada (27.9% of world production) and Australia(22.8%) being the largest producers and Kazakhstan (10.5%),Sony VAIO VGN-AW73FB Battery

Russia (8.0%), Namibia (7.5%), Niger (7.4%), Uzbekistan (5.5%), the United States (2.5%), Argentina (2.1%), Ukraine (1.9%) and China (1.7%) also producing significant amounts.^[57] Kazakhstan continues to increase production and may have become the world's largest producer of uranium by 2009 with an expected production of 12,826 tonnes, Sony VAIO VGN-AW80NS Battery

compared to Canada with 11,100 tonnes and Australia with 9,430 tonnes.^[58][59] The ultimate available uranium is believed to be sufficient for at least the next 85 years^[49] although some studies indicate underinvestment in the late twentieth century may produce supply problems in the 21st century.^[60] Sony VAIO VGN-AW80S Battery

Kenneth S. Deffeyes and Ian D. MacGregor point out that uranium deposits seem to be log-normal distributed. There is a 300-fold increase in the amount of uranium recoverable for each tenfold decrease in ore grade."^[61] In other words, there is little high grade ore and proportionately much more low grade ore available. Sony VAIO VGN-AW80US Battery

Oxidation states and oxides

Calcined uranium yellowcake as produced in many large mills contains a distribution of uranium oxidation species in various forms ranging from most oxidized to least oxidized. Particles with short residence times in a calciner will generally be less oxidized than those with long retention times or particles recovered in the stack scrubber. Sony VAIO VGN-AW81DS Battery

Uranium content is usually referenced to U₃O₈, which dates to the days of the Manhattan project when U₃O₈ was used as an analytical chemistry reporting standard.

Phase relationships in the uranium-oxygen system are complex. The most important oxidation states of uranium are uranium(IV) and uranium(VI), and their two corresponding oxides are, respectively, uranium dioxide (UO₂) and uranium trioxide (UO₃).^[62] Sony VAIO VGN-AW81JS Battery

Otheruranium oxides such as uranium monoxide (UO), diuranium pentoxide (U₂O₅), and uranium peroxide (UO₄·2H₂O) also exist.

The most common forms of uranium oxide are triuranium octaoxide (U₃O₈) and UO₂.^[63] Both oxide forms are solids that have low solubility in water and are relatively stable over a wide range of environmental conditions. Sony VAIO VGN-AW81YS Battery

Triuranium octaoxide is (depending on conditions) the most stable compound of uranium and is the form most commonly found in nature. Uranium dioxide is the form in which uranium is most commonly used as a nuclear reactor fuel.^[63] At ambient temperatures, UO₂ will gradually convert to U₃O₈. Sony VAIO VGN-AW82DS Battery

Because of their stability, uranium oxides are generally considered the preferred chemical form for storage or disposal.^[63]

Aqueous chemistry

Salts of all four oxidation states of uranium are water-soluble and may be studied in aqueous solutions. Sony VAIO VGN-AW82JS Battery

The oxidation states are U³⁺(brown-red), U⁴⁺ (green), UO₂⁺ (unstable), and UO₂²⁺ (yellow).^[64] A few solid and semi-metallic compounds such as UO and US exist for the formal oxidation state uranium(II), but no simple ions are known to exist in solution for that state. Sony VAIO VGN-AW82YS Battery

Ions of U³⁺liberate hydrogen fromwater and are therefore considered to be highly unstable. The UO₂²⁺ ion represents the uranium(VI) state and is known to form compounds such as uranyl carbonate, uranyl chloride and uranyl sulfate. UO₂²⁺ also forms complexes with various organic chelating agents, the most commonly encountered of which is uranyl acetate.^[64] Sony VAIO VGN-AW83FS Battery

Carbonates

The interactions of carbonate anions with uranium(VI) cause the Pourbaix diagram to change greatly when the medium is changed from water to a carbonate containing solution. While the vast majority of carbonates are insoluble in water (students are often taught that all carbonates other than those of alkali metals are insoluble in water), Sony VAIO VGN-AW83GS Battery

uranium carbonates are often soluble in water. This is because a U(VI) cation is able to bind two terminal oxides and three or more carbonates to form anionic complexes.

Effects of pH

The uranium fraction diagrams in the presence of carbonate illustrate this further: Sony VAIO VGN-AW83HS Battery

when the pH of a uranium(VI) solution increases, the uranium is converted to a hydrated uranium oxide hydroxide and at high pHs it becomes an anionic hydroxide complex.

When carbonate is added, uranium is converted to a series of carbonate complexes if the pH is increased. Sony VAIO VGN-AW90NS Battery

One effect of these reactions is increased solubility of uranium in the pH range 6 to 8, a fact which has a direct bearing on the long term stability of spent uranium dioxide nuclear fuels.

Hydrides, carbides and nitrides

Uranium metal heated to 250 to 300 °C (482 to 572 °F) reacts with hydrogen to form uranium hydride. Even higher temperatures will reversibly remove the hydrogen. Sony VAIO VGN-AW90S Battery

This property makes uranium hydrides convenient starting materials to create reactive uranium powder along with various uranium carbide, nitride, and halidecompounds.^[66] Two crystal modifications of uranium hydride exist: an ? form that is obtained at low temperatures and a ? form that is created when the formation temperature is above 250 °C.^[66] Sony VAIO VGN-AW90US Battery

Uranium carbides and uranium nitrides are both relatively inert semimetallic compounds that are minimally soluble in acids, react with water, and can ignite in airto form U₃O₈.^[66] Carbides of uranium include uranium monocarbide (UC), uranium dicarbide (UC₂), and diuranium tricarbide (U₂C₃). Sony VAIO VGN-AW91CDS Battery

Both UC and UC₂ are formed by adding carbon to molten uranium or by exposing the metal to carbon monoxide at high temperatures. Stable below 1800 °C, U₂C₃ is prepared by subjecting a heated mixture of UC and UC₂ to mechanical stress.^[67] Uranium nitrides obtained by direct exposure of the metal to nitrogen include uranium mononitride (UN), uranium dinitride (UN₂), and diuranium trinitride (U₂N₃).^[67] Sony VAIO VGN-AW91CJS Battery

All uranium fluorides are created using uranium tetrafluoride (UF₄); UF₄ itself is prepared by hydrofluorination of uranium dioxide.^[66] Reduction of UF₄ with hydrogen at 1000 °C produces uranium trifluoride (UF₃). Under the right conditions of temperature and pressure, the reaction of solid UF₄ with gaseous uranium hexafluoride (UF₆) can form the intermediate fluorides ofU₂F₉, U₄F₁₇, and UF₅.^[66] Sony VAIO VGN-AW91CYS Battery

At room temperatures, UF₆ has a high vapor pressure, making it useful in the gaseous diffusion process to separate uranium-235 from the common uranium-238 isotope. This compound can be prepared from uranium dioxide and uranium hydride by the following process:^[66] Sony VAIO VGN-AW91DS Battery

UO₂ + 4 HF ? UF₄ + 2 H₂O (500 °C, endothermic)

UF₄ + F₂ ? UF₆ (350 °C, endothermic)

The resulting UF₆, a white solid, is highly reactive (by fluorination), easily sublimes (emitting a nearly perfect gas vapor), and is the most volatile compound of uranium known to exist.^[66] Sony VAIO VGN-AW91JS Battery

One method of preparing uranium tetrachloride (UCl₄) is to directly combine chlorine with either uranium metal or uranium hydride. The reduction of UCl₄ by hydrogen produces uranium trichloride (UCl₃) while the higher chlorides of uranium are prepared by reaction with additional chlorine.^[66] All uranium chlorides react with water and air. Sony VAIO VGN-AW91YS Battery

Bromides and iodides of uranium are formed by direct reaction of, respectively, bromine and iodine with uranium or by adding UH₃to those element's acids.^[66] Known examples include: UBr₃, UBr₄, UI₃, and UI₄. Uranium oxyhalides are water-soluble and include UO₂F₂, UOCl₂, UO₂Cl₂, and UO₂Br₂. Stability of the oxyhalides decrease as the atomic weight of the component halide increases.^[66] Sony VAIO VGN-AW92CDS Battery

Natural concentrations

Natural uranium consists of three major isotopes: uranium-238 (99.28% natural abundance), uranium-235 (0.71%), and uranium-234 (0.0054%). All three are radioactive, emitting alpha particles, with the exception that all three of these isotopes have small probabilities of undergoing spontaneous fission, rather than alpha emission. Sony VAIO VGN-AW92CJS Battery

Uranium-238 is the most stable isotope of uranium, with a half-life of about 4.468×10⁹ years, roughly the age of the Earth. Uranium-235 has a half-life of about 7.13×10⁸ years, and uranium-234 has a half-life of about 2.48×10⁵ years.^[68] For natural uranium, about 49% of its alpha rays are emitted by each of ²³⁸U atom, and also 49% by ²³⁴U Sony VAIO VGN-AW92CYS Battery

(since the latter is formed from the former) and about 2.0% of them by the ²³⁵U. When the Earth was young, probably about one-fifth of its uranium was uranium-235, but the percentage of ²³⁴U was probably much lower than this. Sony VAIO VGN-AW92DS Battery

Uranium-238 is usually an ? emitter – unless it undergoes spontaneous fission – decaying through the "Uranium Series" of nuclear decay, which has 18 members, all of which eventually decay into lead-206, by a variety of different decay paths.^[9] Sony VAIO VGN-AW92JS Battery

The decay series of ²³⁵U, which is called the "Actinium Series" has 15 members, all of which eventually decay into lead-207.^[9] The constant rates of decay in these decay series makes the comparison of the ratios of parent to daughter elements useful in radiometric dating.

Uranium-234 is a member of the "Uranium Series", and it decays to lead-206 through a series of relatively short-lived isotopes. Sony VAIO VGN-AW92YS Battery

Uranium-233 is made from thorium-232 by neutron bombardment, usually in a nuclear reactor, and ²³³U is also fissile.^[8] Its decay series ends with thallium-205.

Uranium-235 is important for both nuclear reactors and nuclear weapons, because it is the only uranium isotope existing in nature on Earth in any significant amount that is fissile. Sony VAIO VGN-AW93FS Battery

This means it can be split into two or three fragments (fission products) by thermal neutrons.^[9]

Uranium-238 is not fissile, but is a fertile isotope, because after neutron activation it can produce plutonium-239, another fissile isotope. Sony VAIO VGN-AW93GS Battery

Indeed, the ²³⁸U nucleus can absorb one neutron to produce the radioactive isotope uranium-239. ²³⁹U decays by beta emission to neptunium-239, also a beta-emitter, that decays in its turn, within a few days into plutonium-239. ²³⁹Pu was used as fissile material in the first atomic bomb detonated in the "Trinity test" on 15 July 1945 in New Mexico.^[22] Sony VAIO VGN-AW93HS Battery

Enrichment

In nature, uranium is found as uranium-238 (99.2742%) and uranium-235 (0.7204%). Isotope separation concentrates (enriches) the fissionable uranium-235 for nuclear weapons and most nuclear power plants, except for gas cooled reactors and pressurised heavy water reactors. Sony VAIO VGN-AW93ZFS Battery

Most neutrons released by a fissioning atom of uranium-235 must impact other uranium-235 atoms to sustain thenuclear chain reaction. The concentration and amount of uranium-235 needed to achieve this is called a 'critical mass'.

To be considered 'enriched', the uranium-235 fraction should be between 3% and 5%.^[69] Sony VAIO VGN-AW93ZGS Battery

This process produces huge quantities of uranium that is depleted of uranium-235 and with a correspondingly increased fraction of uranium-238, called depleted uranium or 'DU'. To be considered 'depleted', the uranium-235 isotope concentration should be no more than 0.3%.^[70] Sony VAIO VGN-AW93ZHS Battery



The price of uranium has risen since 2001, so enrichment tailings containing more than 0.35% uranium-235 are being considered for re-enrichment, driving the price of depleted uranium hexafluoride above $130 per kilogram in July, 2007 from $5 in 2001.^[70]

The gas centrifuge process, where gaseous uranium hexafluoride (UF₆) is separated by the difference in molecular weight between²³⁵UF₆ and ²³⁸UF₆ using high-speed centrifuges, Sony VAIO VGN-BZ11EN Battery

is the cheapest and leading enrichment process.^[21] The gaseous diffusionprocess had been the leading method for enrichment and was used in the Manhattan Project. In this process, uranium hexafluoride is repeatedly diffused through a silver-zinc membrane, and the different isotopes of uranium are separated by diffusion rate (since uranium 238 is heavier it diffuses slightly slower than uranium-235).^[21] Sony VAIO VGN-BZ11MN Battery

The molecular laser isotope separation method employs alaser beam of precise energy to sever the bond between uranium-235 and fluorine. This leaves uranium-238 bonded to fluorine and allows uranium-235 metal to precipitate from the solution.^[5] An alternative laser method of enrichment is known as atomic vapor laser isotope separation (AVLIS) and employs visible tunable lasers such as dye lasers.^[71] Sony VAIO VGN-BZ11XN Battery

Another method used is liquid thermal diffusion.^[7]

Human exposure

A person can be exposed to uranium (or its radioactive daughters such as radon) by inhaling dust in air or by ingesting contaminated water and food. The amount of uranium in air is usually very small; Sony VAIO VGN-BZ12VN Battery

however, people who work in factories that process phosphatefertilizers, live near government facilities that made or tested nuclear weapons, live or work near a modern battlefield where depleted uranium weapons have been used, or live or work near a coal-fired power plant, facilities that mine or process uranium ore, or enrich uranium for reactor fuel, may have increased exposure to uranium.^[72][73] Sony VAIO VGN-BZ12XN Battery

Houses or structures that are over uranium deposits (either natural or man-made slag deposits) may have an increased incidence of exposure to radon gas.

Most ingested uranium is excreted during digestion. Only 0.5% is absorbed when insoluble forms of uranium, such as its oxide, are ingested, whereas absorption of the more soluble uranyl ion can be up to 5%.^[17] Sony VAIO VGN-BZ31VT Battery

However, soluble uranium compounds tend to quickly pass through the body whereas insoluble uranium compounds, especially when inhaled by way of dust into the lungs, pose a more serious exposure hazard. After entering the bloodstream, the absorbed uranium tends to bioaccumulate and stay for many years in bone tissue because of uranium's affinity for phosphates.^[17] Sony VAIO VGN-BZ31XT Battery

Uranium is not absorbed through the skin, and alpha particlesreleased by uranium cannot penetrate the skin.

Incorporated uranium becomes uranyl ions, which accumulate in bone, liver, kidney, and reproductive tissues. Uranium can be decontaminated from steel surfaces^[74]and aquifers.^[75] Sony VAIO VGN-BZ560 Battery

Effects and precautions

Normal functioning of the kidney, brain, liver, heart, and other systems can be affected by uranium exposure, because, besides being weakly radioactive, uranium is atoxic metal.^[17][76][77] Uranium is also a reproductive toxicant.^[78][79] Sony VAIO VGN-BZ560N24 Battery

Radiological effects are generally local because alpha radiation, the primary form of ²³⁸U decay, has a very short range, and will not penetrate skin. Uranyl(UO₂+
) ions, such as from uranium trioxide or uranyl nitrate and other hexavalent uranium compounds, have been shown to cause birth defects and immune system damage in laboratory animals.^[80] Sony VAIO VGN-BZ560N30 Battery

While the CDC has published one study that no human cancer has been seen as a result of exposure to natural or depleted uranium,^[81] exposure to uranium and its decay products, especially radon, are widely known and significant health threats.^[12] Exposure to strontium-90, iodine-131, and other fission products is unrelated to uranium exposure, Sony VAIO VGN-BZ560P Battery

but may result from medical procedures or exposure to spent reactor fuel or fallout from nuclear weapons.^[82]Although accidental inhalation exposure to a high concentration of uranium hexafluoride has resulted in human fatalities, those deaths were associated with generation of highly toxic hydrofluoric acid and uranyl fluoride rather than with uranium itself.^[83] Sony VAIO VGN-BZ560P20 Battery

Sony VAIO VGN-BZ560P22 Battery

Finely divided uranium metal presents a fire hazard because uranium is pyrophoric; small grains will ignite spontaneously in air at room temperature.^[8]

Uranium metal is commonly handled with gloves as a sufficient precaution.^[84] Uranium concentrate is handled and contained so as to ensure that people do not inhale or ingest it. Sony VAIO VGN-BZ560P28 Battery

Neptunium is a chemical element with the symbol Np and atomic number 93. A radioactivemetal, neptunium is the first transuranic element and belongs to the actinide series. Its most stable isotope, ²³⁷Np, is a by-product of nuclear reactorsand plutonium production and it can be used as a component in neutron detection equipment. Sony VAIO VGN-BZ560P30 Battery

Neptunium is also found in trace amounts in uranium ores due to transmutation reactions.^[3]

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 publication of the known radioactive isotopes by Kasimir Fajans shows the empty place after uranium.^[4] Sony VAIO VGN-BZ560P34 Battery

At least three times, discoveries of the element 93 were falsely reported, as bohemium and ausonium in 1934 and thensequanium in 1939. The name neptunium has previously been considered for other elements. Sony VAIO VGN-BZ561 Battery

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 actinides series and therefore placed thorium below hafnium, protactinium below tantalum and uranium below tungsten. Sony VAIO VGN-BZ561N20 Battery

This periodic table suggested that element 93, at that point often named eka-rhenium, should be similar to manganese or rhenium. With this misconception it was impossible to isolate element 93 from minerals although later neptunium was found in uranium ore in 1952.^[5]

Enrico Fermi believed that bombarding uranium with neutrons and subsequent beta decay would lead to the formation of element 93. Sony VAIO VGN-BZ561P20 Battery

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,^[6] though this was soon found to be mistaken. Soon it was speculated^[7] and later proven^[8] that most of the material is created by nuclear fission of uranium by neutrons. Sony VAIO VGN-BZ562P Battery

Small quantities of neptunium had to be produced in Otto Hahn's experiments in late 1930s as a result of decay of ²³⁹U. Hahn and his colleagues experimentally confirmed production and chemical properties of ²³⁹U, but were unsuccessful at isolating and detecting neptunium.^[9Sony VAIO VGN-BZ563P Battery

Neptunium (named for the planet Neptune, the next planet out from Uranus, after which uranium was named) was discoveredbyEdwin McMillan and Philip H. Abelson in 1940 at the Berkeley Radiation Laboratory of the University of California, Berkeley. The team produced the neptunium isotope ²³⁹Np (2.4 day half-life) by bombarding uranium with slow moving neutrons. Sony VAIO VGN-BZAAFS Battery

It was the first transuranium element produced synthetically and the first actinide series transuranium element discovered.^[10]

Occurrence

Trace amounts of neptunium are found naturally as decay products from transmutation reactions in uranium ores.^[3]Artificial²³⁷Np is produced through the reduction of ²³⁷NpF₃ with barium or lithium vapor at around 1200 °C and is most often extracted from spent nuclear fuel rods as a by-product in plutonium production. Sony VAIO VGN-BZAAHS Battery

2 NpF₃ + 3 Ba ? 2 Np + 3 BaF₂

By weight, neptunium-237 discharges are about 5% as great as plutonium discharges and about 0.05% of spent nuclear fueldischarges.^[11]

Characteristics

Silvery in appearance, neptunium metal is fairly chemically reactive and is found in at least three allotropes:^[3] Sony VAIO VGN-BZAANS Battery

• ?-neptunium, orthorhombic, density 20.45 g/cm^3[12]


• ?-neptunium (above 280 °C), tetragonal, density (313 °C) 19.36 g/cm^3[12]


• ?-neptunium (above 577 °C), cubic, density (600 °C) 18 g/cm^3[12]

Neptunium has the largest liquid range of any element, 3363 K, between the melting point and boiling point. It is the densest element of all actinoids. Sony VAIO VGN-BZAAPS Battery

19 neptunium radioisotopes have been characterized, with the most stable being ²³⁷Np with a half-life of 2.14 million years,²³⁶Np with a half-life of 154,000 years, and ²³⁵Np 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. Sony VAIO VGN-CR11H/B Battery

This element also has 4 meta states, with the most stable being ^236mNp (t_½ 22.5 hours).

The isotopes of neptunium range in atomic weight from 225.0339 u (²²⁵Np) to 244.068 u (²⁴⁴Np). The primary decay mode before the most stable isotope, ²³⁷Np, is electron capture (with a good deal of alpha emission), and the primary mode after is beta emission. Sony VAIO VGN-CR11S/L Battery

The primary decay products before ²³⁷Np are element 92 (uranium) isotopes (alpha emission produces element 91,protactinium, however) and the primary products after are element 94 (plutonium) isotopes.

²³⁷Np is fissionable.^{[13] 237}Np eventually decays to form bismuth-209, unlike most other common heavy nuclei which decay to make isotopes of lead. This decay chain is known as the neptunium series. Sony VAIO VGN-CR11S/P Battery

Synthesis

Chemically, neptunium is prepared by the reduction of NpF₃ with barium or lithium vapor at about 1200 °C.^[3] Most Np is produced in nuclear reactions:

When an ²³⁵U atom captures a neutron, it is converted to an excited state of ²³⁶U. Sony VAIO VGN-CR11S/W Battery

About 81% of the excited ²³⁶U nuclei undergo fission, but the remainder decay to the ground state of ²³⁶U by emitting gamma radiation. Further neutron capturecreates ²³⁷U which has a half-life of 7 days and thus quickly decays to ²³⁷Np through beta decay. During beta decay, the excited ²³⁷U emits an electron, while the atomic weak interaction converts a neutron to a proton, thus creating ²³⁷Np. Sony VAIO VGN-CR11Z/R Battery

• ²³⁷U is also produced via an (n,2n) reaction with ²³⁸U. This only happens with very energetic neutrons.


• ²³⁷Np is the product of alpha decay of ²⁴¹Am.

Heavier isotopes of neptunium decay quickly, and lighter isotopes of neptunium cannot be produced by neutron capture, so chemical separation of neptunium from cooledspent nuclear fuel gives nearly pure ²³⁷Np. Sony VAIO VGN-CR120E/L Battery

Chemistry

This element has four ionic oxidation states while in solution:

• Np³⁺ (pale purple), analogous to the rare earth ion Pm³⁺


• Np⁴⁺ (yellow green)


• NpO₂⁺ (green blue)


• NpO₂²⁺ (pale pink)

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).^[14][15] Sony VAIO VGN-CR120E/P Battery

Neptunium forms tri- and tetrahalides such as NpF₃, NpF₄, NpCl₄, NpBr₃, NpI₃, and oxides of the various compositions such as are found in the uranium-oxygen system, including Np₃O₈ and NpO₂.

Neptunium(VI) fluoride, NpF₆, is volatile like uranium hexafluoride. Sony VAIO VGN-CR120E/R Battery

Neptunium, like protactinium, uranium, plutonium, and americium readily forms a linear dioxo neptunyl core (NpO₂ⁿ⁺), in its 5+ and 6+ oxidation states, which readily complexes with hard O-donor ligands such as OH^–, NO₂^–, NO₃^–, and SO₄^2– to form soluble anionic complexes which tend to be readily mobile with low affinities to soil. Sony VAIO VGN-CR120E/W Battery

Precursor in plutonium-238 production

²³⁷Np is irradiated with neutrons to create ²³⁸Pu, an alpha emitter for radioisotope thermal generators for spacecraft and military applications. ²³⁷Np will capture a neutron to form ²³⁸Np and beta decay with a half-life of two days to ²³⁸Pu.^[16] Sony VAIO VGN-CR125E/B Battery

²³⁸Pu also exists in sizable quantities in spent nuclear fuel but would have to be separated from other isotopes of plutonium.

Weapons applications

Neptunium is fissionable, and could theoretically be used as fuel in a fast neutron reactor or a nuclear weapon. Sony VAIO VGN-CR13/B Battery

In 1992, the U.S. Department of Energy declassified the statement that neptunium-237 "can be used for a nuclear explosive device".^[17] 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. Sony VAIO VGN-CR13/L Battery

In September 2002, researchers at the University of California's 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,"^[1] showing that it "is about as good a bomb material as U-235."^[13] Sony VAIO VGN-CR13/P Battery

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.

Physics applications

²³⁷Np is used in devices for detecting high-energy (MeV) neutrons.^[18] Sony VAIO VGN-CR13/R Battery

Role in nuclear waste

Neptunium-237 is the most mobile actinide in the deep geological repository environment.^[19] This makes it and its predecessors such as americium-241 candidates of interest for destruction by nuclear transmutation.^[20] Sony VAIO VGN-CR13/W Battery

Neptunium accumulates in commercial household ionization-chamber smoke detectors 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. Sony VAIO VGN-CR131E/L Battery

Sony VAIO VGN-CR13G Battery

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. Sony VAIO VGN-CR13G/B Battery,Sony VAIO VGN-CR13G/L Battery,Sony VAIO VGN-CR13G/P Battery,Sony VAIO VGN-CR13G/R Battery,Sony VAIO VGN-CR13G/W Battery,Sony VAIO VGN-CR13T/L Battery,Sony VAIO VGN-CR13T/P Battery,Sony VAIO VGN-CR13T/R Battery,Sony VAIO VGN-CR13T/W Battery,Sony VAIO VGN-CR15/B Battery,Sony VAIO VGN-CR150E/B Battery