Uranium

Notable characteristics

When refined, uranium is a silvery white, weakly radioactive metal, which is slightly softer than steel. It is malleable, ductile, and slightly paramagnetic. Uranium metal has very high density, 65% more dense than lead. When finely divided, it can react with cold water; in air, uranium metal becomes coated with uranium oxide. Uranium in ores can be extracted and chemically converted into uranium dioxide or other chemical forms usable in industry.

Related Topics:
Steel - Paramagnetic - Density - Lead - Uranium dioxide

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Uranium metal has three allotropic forms:

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• alpha (orthorhombic) stable up to 667.7 °C
• beta (tetragonal) stable from 667.7 °C to 774.8 °C
• 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. 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.

Related Topics:
²³⁵U - ²³⁸U - ²³⁴U - Nuclear reactor - Nuclear weapon - Neutron - Plutonium

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The artificial 233U isotope is also fissile and is made from 232thorium by neutron bombardment.

Related Topics:
²³³U - Thorium - Neutron

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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 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.

Related Topics:
Nuclear chain reaction - Nuclear fission - Nuclear fusion

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