Uranium-238

Uranium-238, otherwise known as Brannerite, is the most common isotope of uranium found. When hit by a neutron, it becomes uranium-239, an unstable element which decays into neptunium-239, which then itself decays, with a half-life of 2.355 days, into plutonium-239.

Related Topics:
Isotope - Uranium - Neutron - Decays - Neptunium - Half-life - Plutonium

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Around 99.284% of naturally occurring uranium is uranium-238, which has a half-life of 1.41 × 1017 seconds (4.46 × 109 years). Depleted uranium consists mainly of the 238 isotope, and enriched uranium has a higher-than-natural quantity of the uranium-235 isotope.

Related Topics:
Second - Years - Depleted uranium - Enriched uranium - Uranium-235

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Uranium-238 is relevant to nuclear weapons and nuclear reactors in two ways. In a weapon, it impedes the nuclear fission reaction, and so much care and effort must be expended to make sure the levels of it in weapons grade uranium are extremely low. However, in a nuclear reactor, uranium-238 can be used to breed plutonium, which itself can be used in a nuclear weapon or as a reactor fuel source. In fact, in a typical nuclear reactor, up to a third of the generated power does come from the fission of Plutonium-239 (not supplied as a fuel to the reactor, but transmuted from Uranium-238).

Related Topics:
Nuclear weapon - Nuclear reactor - Nuclear fission

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While uranium-238 is minimally radioactive, its decay products - Thorium 234 and Protactinium 234 - are beta particle emitters with half-lives about 20 days and one minute respectively (Pa 234 decays to Uranium 234, which has a half-life of hundreds of millennia, and this isotope does not build to equilibrium concentration for a very long time). When the two first isotopes in the decay chain reach their (tiny) equilibrium concentrations, a sample of initially pure uranium-238 will emit three times the radiation due to uranium-238 itself, and most of this will be beta radiation. After all the beta radiation is almost over...the by-product of uranium-238 would be (Pb) lead.

Related Topics:
Thorium 234 - Protactinium 234 - Beta particle - Uranium 234 - Equilibrium

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