Jump to content

Uranium–uranium dating

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by Actinide (talk | contribs) at 03:05, 11 July 2005 (Added explanation of importance of initial state, plus minor changes - removed 14C and K-Ar as relate to completely different materials). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Uranium-uranium dating is a radiometric dating technique utilizing the comparison of two isotopes of uranium in a sample: uranium-238 and uranium-234. Uranium-uranium dating is one of several radiometric dating techniques exploiting the uranium radioactive decay series, in which U-238 undergoes 14 alpha and beta decay events while decaying to the stable isotope lead-206. Other dating techniques using this decay series include uranium-thorium and uranium-lead dating.

U-238, with a half-life of about 4.5 billion years, decays to U-234 through emission of an alpha particle to thorium-234, which is comparatively unstable with a half-life of just 24 days. Th-234 then decays through beta particle emission to protactinium-234. Pa-234 decays with a half-life of 6.7 hours, again through emission of a beta particle, to U-234. This isotope has a half-life of about 245,000 years. The next decay product, Th-230, has a half-life of about 75,000 years and is used for the related uranium-thorium dating technique. Although analytically simpler than uranium-thorium dating, in practice uranium-uranium dating is almost never used as unlike uranium-thorium dating it requires prior knowldege of the U-234/U-238 ratio at the time the material under study was formed. For those materials (principally marine carbonates) for which the initial ratio is known, uranium-thorium dating remains a superior technique. This restricts the application of uranium-uranium to extremely rare cases where the initial U-234/U-238 ratio is well-constrained and the sample is also beyond the ca. 450,000 year upper limit of the uranium-thorium technique.

Unlike other radiometric dating techniques, those using the uranium decay series (except for those using the stable final isotopes Pb-206 and Pb-207) 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 uranium-uranium 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 U-234. As such, it provides a useful bridge in radiometric dating techniques between the ranges of uranium-thorium dating (accurate up to ca. 450,000 years) and uranium-lead dating (accurate up to the age of the solar system, but problematic on samples younger than about 2 million years).

Reference

Retrieved from "https://en.wikipedia.org/w/index.php?title=Uranium–uranium_dating&oldid=18573208"