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Uranium-uranium datingUranium-uranium dating is a radiometric dating technique utilizing the comparison of two isotopes of uranium (U) in a sample: ^{238}U and ^{234}U. ^{234}U/^{238}U dating is one of several radiometric dating techniques exploiting the uranium radioactive decay series, in which ^{238}U undergoes 14 alpha and beta decay events while decaying to the stable isotope ^{206}Pb. Other dating techniques using this decay series include uranium-thorium (using ^{230}Th/^{238}U) and uranium-lead dating. Additional recommended knowledge^{238}U, with a half-life of about 4.5 billion years, decays to ^{234}U through emission of an alpha particle to an isotope of thorium (^{234}Th), which is comparatively unstable with a half-life of just 24 days. ^{234}Th then decays through beta particle emission to an isotope of protactinium, ^{234}Pa. ^{234}Pa decays with a half-life of 6.7 hours, again through emission of a beta particle, to ^{234}U. This isotope has a half-life of about 245,000 years. The next decay product, ^{230}Th, has a half-life of about 75,000 years and is used for the related ^{230}Th/^{238}U technique. Although analytically simpler than ^{230}Th/^{238}U dating, in practice ^{234}U/^{238}U dating is almost never used as unlike ^{230}Th/^{238}U dating it requires prior knowldege of the ^{234}U/^{238}U ratio at the time the material under study was formed. For those materials (principally marine carbonates) for which the initial ratio is known, ^{230}Th/^{238}U remains a superior technique. This restricts the application of ^{234}U/^{238}U to extremely rare cases where the initial ^{234}U/^{238}U is well-constrained and the sample is also beyond the ca. 450,000 year upper limit of the ^{230}Th/^{238}U technique. Unlike other radiometric dating techniques, those using the uranium decay series (except for those using the stable final isotopes ^{206}Pb and ^{207}Pb) compare the ratios of two radioactive unstable isotopes. This complicates calculations as both the parent and daughter isotopes decay over time into other isotopes. In theory, the ^{234}U/^{238}U technique can be useful in dating samples between about 10,000 and 2 million years Before Present (BP), or up to about eight times the half-life of ^{234}U. As such, it provides a useful bridge in radiometric dating techniques between the ranges of ^{230}Th/^{238}U (accurate up to ca. 450,000 years) and U-Pb dating (accurate up to the age of the solar system, but problematic on samples younger than about 2 million years).
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Categories: Radiometric dating | Uranium |
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Uranium-uranium_dating". A list of authors is available in Wikipedia. |