Protactinium—thorium dating , method of age determination that makes use of the quantities of certain protactinium and thorium isotopes in a marine sediment. Protactinium and thorium have very similar chemical properties and appear to be precipitated at the same rates in marine sediments. The isotopes protactinium and thorium are both radioactive and decay with half-lives of 32, years and 80, years, respectively. The ratio of the two radioactive isotopes constitutes a better radioactive geochronometer than either of them separately, because they do not need to have a uniform sedimentation rate through time but need only be precipitated in the same proportion. It is likely that this condition will hold even though the rate of sedimentation may vary.
Thorium - Cancer-Causing Substances - National Cancer Institute
Ionium-thorium dating , method of establishing the time of origin of marine sediments according to the amount of ionium and thorium they contain. Because uranium compounds are soluble in seawater, while thorium compounds are quite insoluble, the thorium isotopes produced by the decay of uranium in seawater are readily precipitated and incorporated in sediments. One of these thorium isotopes, thorium also known as ionium , has a half-life of about 80, years, which makes it suitable for dating sediments as old as , years. Thus, the amount of ionium in sediments can be used as a rough measure of the age of sediment.
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Human Fossils: Uranium-Series Dating Method
Uranium—uranium dating is a radiometric dating technique which compares two isotopes of uranium U in a sample: uranium U and uranium U. It is one of several radiometric dating techniques exploiting the uranium radioactive decay series , in which U undergoes 14 alpha and beta decay events on the way to the stable isotope Pb. Other dating techniques using this decay series include uranium—thorium dating and uranium—lead dating.
Uranium—thorium dating , also called thorium dating , uranium-series disequilibrium dating or uranium-series dating , is a radiometric dating technique established in the s which has been used since the s to determine the age of calcium carbonate materials such as speleothem or coral. Instead, it calculates an age from the degree to which secular equilibrium has been restored between the radioactive isotope thorium and its radioactive parent uranium within a sample. Thorium is not soluble in natural water under conditions found at or near the surface of the earth, so materials grown in or from this water do not usually contain thorium. As time passes after such material has formed, uranium in the sample with a half-life of , years decays to thorium At secular equilibrium, the number of thorium decays per year within a sample is equal to the number of thorium produced, which also equals the number of uranium decays per year in the same sample.