Uranium (U) is a heavy, soft, silvery-white, metallic element, radioactive, easily oxidized, and having 14 known isotopes of which ²³⁸U is the most abundant in nature. It has the highest atomic number (92) of any naturally occurring metal. Uranium is in the actinide series. It occurs in several ores, including pitchblende (uraninite), carnotite, autunite, and torbernite from which it is extracted and processed for use in research and nuclear fuels. Uranium was discovered in 1789 by Martin Kaproth.

 

The naturally occurring isotopes are fissionable ²³⁵U (0.7205% of natural uranium), ²³⁸U which cannot be fissioned with thermal neutrons (99.2739% of natural uranium), and ²³⁴U, a decay product of ²³⁸U (0.0056%). Enriched uranium is that in which the percentage of the fissionable isotope ²³⁵U has increased beyond the content of 0.7205% of natural uranium. Depleted uranium has a lower percentage of ²³⁵U than that occurring in natural uranium; it is produced during uranium isotope separation.

 

The decay of uranium yields a series (see radioactive series) of radioactive products, including radium and radon. Exposure to the radiation emitted by uranium can cause tissue damage or cancer. Uranium is also chemically poisonous and can cause damage to the urinary system.

 

atomic number	92
relative atomic mass	238.03
melting point	1,132°C (2,070°F)
boiling point	3,818°C (6,904°F)
relative density	18.95

 

Uranium is found in many ores, including carnotite shown here.

 

Uranium oxide

One of a series of compounds of which UO₂, U₄O₉, U₃O₈, and UO₃ are the most common, and of which U₃O₈ is the most stable. The latter is green, brown, or black with an orthorhombic crystalline structure.