Uranium

Symbol: U Atomic Number: 92 Atomic Mass: 238.03

Uranium is a chemical element with the symbol U and the atomic number 92. It is an actinide. It is a solid element with a density of 19.1 g*cm^-3 and a boiling point of 4404 K. U-238, U-235, and U-234 are most commonly found in nature, and because of the slow rate of decay they are incredibly useful when dating the age of the earth. Radioactive U-238 was used in atomic bombs in World War II.



**The theory and uses of natural uranium isotopic variations in hydrology** Osmond, J K | Cowart, J B **Atomic Energy Review. Vol. 14-, no. 4, pp. 621-679. 1976**

The authors summarize developments in the field of uranium-234 /uranium-238 disequilibrium studies and focus on terrestrial hydrogeochemistry. The dissolved concentration of uranium and the relative abundance of the two uranium isotopes in natural waters vary over a wide range of values and are controlled principally by the redox potential of the environment and by carbon dioxide. Ion exchange and alpha-spectrometry techniques are described which permit the measurement of uranium at concentrations as low as p.p.10 11 and the isotopic ratio to a few per cent. In oxidizing conditions it is shown that the uranium isotopes behave in a chemically stable conservative manner such that separate ground-water sources may have identifiably different characteristics and mixing volume calculations may be made. The use of these isotopes in radiometric dating, the tracing of hydrologic systems, reservoir analysis, geothermal systems and sediment-water interactions are illustrated. A bibliography of 192 references is appended.

Radioactive Uranium was discovered by Martin Heinrich Klaproth, a German chemist, in the mineral pitchblende (primarily a mix of uranium oxides) in 1789. Although Klaproth, as well as the rest of the scientific community, believed that the substance he extracted from pitchblende was pure uranium, it was actually uranium dioxide (UO2). After noticing that 'pure' uranium reacted oddly with uranium tetrachloride (UCl4), Eugène-Melchoir Péligot, a French chemist isolated pure uranium by heating uranium dioxide with potassium in a platinum crucible. Radioactivity was first discovered in 1896 when Antoine Henri Becquerel, a French physicist, detected it from a sample of uranium. Today, uranium is obtained from uranium ores such as pitchblende, uraninite (UO2), carnotite (K2(UO2)2VO4·1-3H2O) and autunite (Ca(UO2)2(PO4)2·10H2O) as well as from phosphate rock (Ca3(PO4)2), lignite (brown coal) and monazite sand ((Ce, La, Th, Nd, Y)PO4). Since there is little demand for uranium metal, uranium is usually sold in the form of sodium diuranate (Na2U2O7·6H2O), also known as yellow cake, or triuranium octoxide (U3O8). Since it is naturally radioactive, uranium, usually in the form of uranium dioxide (UO2), is most commonly used in the nuclear power industry to generate electricity. Naturally occurring uranium consists of three isotopes: uranium-234, uranium-235 and uranium-238. Although all three isotopes are radioactive, only uranium-235 is a fissionable material that can be used for nuclear power. When a fissionable material is struck by a neutron, its nucleus can release energy by splitting into smaller fragments. If some of the fragments are other neutrons, they can strike other atoms and cause them to split as well. A fissionable material, such as uranium-235, is a material capable of producing enough free neutrons to sustain a nuclear chain reaction. Only 0.7204% of naturally occurring uranium is uranium-235. This is too low a concentration to sustain a nuclear chain reaction without the help of a material known as a moderator. A moderator is a material that can slow down a neutron without absorbing it. Slow neutrons are more likely to react with uranium-235 and reactors using natural uranium can be made using graphite or heavy water as a moderator. Methods also exist for concentrating uranium-235. Once the levels of uranium-235 have been increased to about 3%, normal water can be used as a moderator. Uranium-238, uranium's most common isotope, can be converted into plutonium-239, a fissionable material that can also be used as a fuel in nuclear reactors. To produce plutonium-239, atoms of uranium-238 are exposed to neutrons. Uranium-239 forms when uranium-238 absorbs a neutron. Uranium-239 has a half-life of about 23 minutes and decays into neptunium-239 through beta decay. Neptunium-239 has a half-life of about 2.4 days and decays into plutonium-239, also through beta decay. Although it does not occur naturally, uranium-233 is also a fissionable material that can be used as a fuel in nuclear reactors. To produce uranium-233, atoms of thorium-232 are exposed to neutrons. Thorium-233 forms when thorium-232 absorbs a neutron. Thorium-233 has a half-life of about 22 minutes and decays into protactinium-233 through beta decay. Protactinium-233 has a half-life of about 27 days and decays into uranium-233, also through beta decay. If completely fissioned, one pound (0.45 kilograms) of uranium-233 will provide the same amount of energy as burning 1,500 tons (1,350,000 kilograms) of coal. Uranium is a dense metal that has uses outside of the nuclear power industry. It is used as a target for X-ray production, as ammunition for some types of military weaponry, as a shield against radiation, as a counterweight for aircraft control surfaces and in the gyroscopes of inertial guidance systems. Uranium compounds have been used for centuries to color glass. A 2,000 year old sample of yellow glass found near Naples, Italy contains uranium oxide. Uranium trioxide (UO3) is an orange powder and has been used in the manufacture of Fiestaware plates. Other uranium compounds have also been used to make vaseline glass and glazes. The uranium within these items is radioactive and should be treated with care. Uranium's most stable isotope, uranium-238, has a half-life of about 4,468,000,000 years. It decays into thorium-234 through alpha decay or decays through spontaneous fission.
 * Atomic Number:** 92
 * Atomic Weight:** 238.02891
 * Melting Point:** 1408 K (1135°C or 2075°F)
 * Boiling Point:** 4404 K (4131°C or 7468°F)
 * Density:** 18.95 grams per cubic centimeter
 * Phase at Room Temperature:** Solid
 * Element Classification:** Metal
 * Period Number:** 7 **Group Number:** none **Group Name:** Actinide
 * What's in a name?** Named for the planet **Uranus**.
 * Say what?** Uranium is pronounced as **you-RAY-nee-em**.
 * History and Uses:**
 * Estimated Crustal Abundance:** 2.7 milligrams per kilogram
 * Estimated Oceanic Abundance:** 3.2×10-3 milligrams per liter
 * Number of Stable Isotopes:** 0
 * Ionization Energy:** 6.194 eV
 * Oxidation States:** +6, +5, +4, +3

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; however, people who work in factories that process [|phosphate] [|fertilizers], 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. [|[73]] [|[74]] 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%. [|[18]] 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. [|[18]] Uranium is not absorbed through the skin, and [|alpha particles] released 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 [|[75]] and [|aquifers]. [|[76]] Examples of where one could find uranium would mainly be in the soil of rocks and of the Earth's crust.