gamma (body-centered cubic) from 774.8°C to melting point - this is the most malleable and ductile state.
Its two principal isotopes are 235U and 238U (see Uranium-235 and Uranium-238). Naturally-occurring Uranium also contains a small amount of the 234U isotope, which is a decay product of 238U. The isotope 235U is important for both nuclear reactors and nuclear weapons because it is the only isotope existing in nature to any appreciable extent that is fissile, that is, fissionable by thermal neutrons. The isotope 238U is also important because it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope 239Pu (plutonium), which also is fissile.
The artificial 233U isotope is also fissile and is made from 232thorium by neutron bombardment.
Uranium was the first element that was found to be fissile, i.e. upon bombardment with slow neutrons, its 235U isotope becomes the very short lived 236U, that immediately divides into two smaller nuclei, liberating energy and more neutrons. If these neutrons are absorbed by other 235U nuclei, a nuclear chain reaction occurs, and if there is nothing to absorb some neutrons and slow the reaction, it is explosive. The first atomic bomb worked with by this principle (nuclear fission). A more accurate name for both this and the hydrogen bomb (nuclear fusion) would be "nuclear weapon", because only the nuclei participate.
Uranium metal is very dense and heavy. Depleted uranium (almost pure U-238 with less than 0.2% U-235) is used by some militaries as shielding to protect tanks, and also in parts of bullets and missiles. The military also uses enriched uranium (more than natural levels of U-235) to power nuclear propelled navy ships and submarines, and in nuclear weapons. Fuel used for United States Navy reactors is typically highly enriched in U-235 (the exact values are classified information). In nuclear weapons uranium is also highly enriched, usually over 90% (again, the exact values are classified information).
The main use of uranium in the civilian sector is to fuel commercial nuclear power plants, where fuel is typically enriched in U-235 to 2-3%. However, the Canadian Candu reactors use natural unenriched uranium as fuel. Depleted uranium is used in helicopters and airplanes as counterweights on certain wing parts. Other uses include;
Ceramic glazes where small amounts of natural uranium (that is, not having gone through the enrichment process) may be added for color.
The long half-life of the isotope uranium-238 (4.51 × 109) make it well-suited for use in estimating the age of the earliest igneous rocks.
U-238 is converted into plutonium in breeder reactors. Plutonium in turn in used in hydrogen bombs.
Some lighting fixtures utilize uranium, as do some photographic chemicals (esp. uranium nitrate).
Phosphatefertilizers often contain high amounts of natural uranium, because the mineral material from which they are made is typically high in uranium.
Uranium metal is used for X-ray targets in making of high-energy X-rays.
The discovery of the element is credited to the German chemist Martin Heinrich Klaproth who in 1789 found uranium as part of the mineral called pitchblende. It was named after the planet Uranus, which had been discovered eight years earlier. It was first isolated as a metal in 1841 by Eugene-Melchior Peligot. Uranium was found to be radioactive by French physicist Henri Becquerel in 1896, who first discovered the process of radioactivity with uranium minerals.
In the Manhattan Project the names tuballoy and oralloy were used to refer to natural uranium and enriched uranium respectively. These names are still used occasionally to refer to natural or enriched uranium.
The exploration and mining of radioactive ores in the United States began around the turn of the 20th century. Sources for radium (contained in uranium ore) were sought for use as luminous paint for watch dials and other instruments. Uranium became important for defense purposes during World War II. In 1943, the Union Mines Development Corporation operated mills in Colorado to process uranium ore for the Manhattan Project, which applied atomic power to military use. To ensure adequate supplies of uranium for national defense, Congress passed the U.S. Atomic Energy Act of 1946, creating the Atomic Energy Commission which had the power to withdraw prospective uranium mining land from public purchase, and also to manipulate the price of uranium to meet national needs (leading to a uranium "boom" in the early 1950s). Military requirements declined in the 1960s, and the Government completed its uranium procurement program by the end of 1970. Simultaneously, a new market emerged - commercial nuclear power plants.
Uranium hexafluoride (UF6) is a white solid which forms a vapor at temperatures above 56 degrees Celsius. UF6 is the compound of uranium used for the two most common enrichment processes, gaseous diffusion enrichment and centrifuge enrichment. It is simply called "hex" in the industry.
Yellowcake is uranium concentrate. It takes its name from the color and texture of the concentrates produced by early mining operations, despite the fact that modern mills using higher calcining temperatures produce "yellowcake" that is dull green to almost black. Yellowcake typically contains 70 to 90 percent uranium oxide (U3O8) by weight.
Ammonium diuranate is an intermediate product in the production of yellowcake, and is bright yellow in colour. It is sometimes confusingly called "yellowcake" as well, but this is not a standard name.
The decay of uranium and its nuclear reactions with thorium in the Earth's core is thought to be the source for much of the heat that keeps the outer core liquid, which in turn drives plate tectonics.
Uranium ore is rock containing uranium mineralization in concentrations that can be mined economically, typically 1 to 4 pounds of uranium oxide per ton or 0.05 to 0.20 percent uranium oxide.
