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Uranium-Thorium dating is an absolute dating technique which uses the properties of the radio-active half-life of Uranium-238 and Thorium-230. The half-life of uranium--238 is 4,470,000,000 years, that is, in that many years half of the original amount is still uranium- the other half has lost protons to form a different element which is more stable. The half-life of thorium-230 is only 75,380 years. When the amounts of uranium and thorium are compared an accurate estimation of the age of an object can be obtained. There are various procedures which can be used with this dating technique. Two processes are Isotope Dilution Mass Spectrometry (IDMS), Secondary Ion Mass Spectrometry (SIMS) and IDMS-Thermal Ionization Mass Spectrometry (TIMS). For each process the IDMS uses an element specific resin to chemically separate the uranium and thorium and remove metals, the latest development for this process is U/teva.SPEC. For any process there must be correction for Thorium-232, the common thorium which is not radioactive. However, once the corrections are made the technique has been checked with Carbon-14 dating and has been found accurate. Uranium-Thorium dating was first used on fossil bones in 1956, however, it had been used for dating wood before this. This dating technique has been used effectively on marine sediment, bone, wood, coral, stone and soil. One of the benefits of uranium-thorium dating is that the sample sizes can be less than 20 grams, in fact bone samples can be 3-5 grams for an accurate date. One problem with the technique is the requirements for the object to be dated- it must take up uranium-238 and no thorium, then immediately be closed off so it would not be able to take in more. This is possible especially in caves, deep water and land fall areas.
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