Uranium-uranium dating

Uranium-uranium dating

Uranium-uranium dating is a radiometric dating technique utilizing the comparison of two isotopes of uranium (U) in a sample: 234U and 238U. 234U/238U dating is one of several radiometric dating techniques exploiting the uranium radioactive decay series, in which 238U undergoes 14 alpha and beta decay events while decaying to the stable isotope 206Pb. Other dating techniques using this decay series include uranium-thorium (using 230Th/238U) and uranium-lead dating.

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

Unlike other radiometric dating techniques, those using the uranium decay series (except for those using the stable final isotopes 206Pb and 207Pb) 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 234U/238U 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 234U. As such, it provides a useful bridge in radiometric dating techniques between the ranges of 230Th/238U (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).

References

* [http://www.webelements.com/webelements/elements/text/Pa/radio.html "Protactinium: Radioisotope Data"] . WebElements. Retrieved July 8, 2005.
*Shakhashiri, Bassam. [http://scifun.chem.wisc.edu/chemweek/uranium/uclock.htm "Chemical of the Week -- Uranium"] . University of Wisconsin-Madison Chemistry Department. Retrieved July 8, 2005.
* [http://www.britannica.com/eb/article?tocId=9074426&query=Uranium-234-Uranium-238%20Dating&ct= "Uranium-234-uranium-238 dating"] . "Encyclopædia Britannica". Retrieved July 8, 2005.


Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • uranium dating — a method of dating archaeological or geological specimens by determining the decay activity of the uranium in a given sample. * * * …   Universalium

  • uranium dating — a method of dating archaeological or geological specimens by determining the decay activity of the uranium in a given sample …   Useful english dictionary

  • Uranium — (pronEng|jʊˈreɪniəm) is a silvery gray metallic chemical element in the actinide series of the periodic table that has the symbol U and atomic number 92. It has 92 protons and 92 electrons, 6 of them valence electrons. It can have between 141 and …   Wikipedia

  • Uranium-234 — Infobox isotope background = #fc6 text color = isotope name = Uranium 234 isotope filename = alternate names = mass number =234 symbol =U num neutrons =142 num protons =92 abundance =0.0055% halflife =246,000 years error halflife = decay product …   Wikipedia

  • Uranium-thorium dating — Uranium thorium dating, also called thorium 230 dating, uranium series disequilibrium dating or uranium series dating, is a radiometric dating technique commonly used to determine the age of carbonate materials such as speleothem or coral [ [http …   Wikipedia

  • Uranium-lead dating — Uranium lead is one of the oldest and most refined radiometric dating schemes, with a routine age range of about 1 million years to over 4.5 billion years, and with routine precisions in the 0.1 1 percent range. [Parrish, Randall R.; Noble,… …   Wikipedia

  • Dating methodologies in archaeology — Dating material drawn from the archaeological record can be made by a direct study of an artifact or may be deduced by association with materials found in the context the item is drawn from or inferred by its point of discovery in the sequence… …   Wikipedia

  • uranium-lead dating — noun (geology) A method of determining the age in years of geological material, based on the known decay rate of uranium isotopes to lead isotopes • • • Main Entry: ↑uranium …   Useful english dictionary

  • dating — I In geology and archaeology, the process of determining an object s or event s place within a chronological scheme. Scientists may use either relative dating, in which items are sequenced on the basis of stratigraphic clues (see stratigraphy) or …   Universalium

  • uranium-thorium-lead dating — or common lead dating Method of dating very old rocks by means of the amount of common lead they contain. Common lead is any lead from a rock or mineral that contains a large amount of lead and a small amount of the radioactive precursors of lead …   Universalium

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”