uranium
Sign in to saveUranium is a chemical element; it has symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium radioactively decays, usually by emitting an alpha particle. The half-life of this decay varies between 159,200 and 4.5 billion years for different isotopes, making them useful for dating the age of the Earth. The most common isotopes in natural uranium are uranium-238 (which has 146 neutrons and accounts for over 99% of uranium on Earth) and uranium-235 (which
AI overview
Uranium is a naturally occurring silvery-grey metal that is radioactive, meaning its atoms gradually break down over time by releasing particles—a process that happens at different rates for different forms of uranium, with some taking billions of years to decay. Because of these different decay rates, uranium is useful for scientists to determine the age of the Earth, and uranium-235 and uranium-238 are the most common forms found in nature.
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Article
35 sectionsContents
- Characteristics
- Applications
- Military
- Civilian
- History
- Pre-discovery use
- Discovery
- Fission research
- Nuclear weaponry
- Reactors
- Prehistoric naturally occurring fission
- Contamination and the Cold War legacy
- Occurrence
- Origin
- Biotic and abiotic
- Production and mining
- Resources and reserves
- Supplies
- Compounds
- Oxidation states and oxides
- Oxides
- Aqueous chemistry
- Carbonates
- Effects of pH
- Hydrides, carbides and nitrides
- Halides
- Isotopes
- Enrichment
- Human exposure
- Effects and precautions
- See also
- Notes
- References
- Sources cited
- External links
Uranium is a chemical element; it has symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium radioactively decays, usually by emitting an alpha particle. The half-life of this decay varies between 159,200 and 4.5 billion years for different isotopes, making them useful for dating the age of the Earth. The most common isotopes in natural uranium are uranium-238 (which has 146 neutrons and accounts for over 99% of uranium on Earth) and uranium-235 (which has 143 neutrons). Uranium has the highest atomic weight of the primordially occurring elements. Its density is about 70% higher than that of lead and slightly lower than that of gold or 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.
Many contemporary uses of uranium exploit its unique nuclear properties. Uranium is used in nuclear power plants and nuclear weapons because it is the only naturally occurring element with a fissile isotope – uranium-235 – present in non-trace amounts. However, because of the low abundance of uranium-235 in natural uranium (which is overwhelmingly uranium-238), uranium needs to undergo enrichment so that enough uranium-235 is present. Uranium-238 is fissionable by fast neutrons and is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor. Another fissile isotope, uranium-233, can be produced from natural thorium and is studied for future industrial use in nuclear technology. 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. 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. The primary civilian use for uranium harnesses the heat energy to produce electricity. Depleted uranium (U) is used in kinetic energy penetrators and armor plating.