Academic Applications  Uses of Nuclear RadiationThe most common and accepted method of 'absolute geologic dating' (establishment of actual age) is based on the natural radioactivity of certain minerals found in rocks. As the rate of radioactive decay of any particular isotope is known, the age of a specimen can be worked out from the ratio of the remaining isotope and its decay product. Dating of Igneous Rocks (Using Uranium Content)Geologists use this method to date igneous rock samples. If you look carefully at the halflives of isotopes in the Uranium Series you appreciate that the uranium has a much longer halflife than any of the others. So, by comparing the proportion of Uranium in the rock to the proportion of lead produced by its decay you can work out how many halflives it has been decaying. Then by using the
halflife of Uranium you can work out the time involved.
Dating of Ancient Artefacts (Carbon Dating)Carbon dating measures the remaining amount of the radioactive isotope carbon14 in organic matter. It can be used to date specimens as old as 35,000 years. During its lifetime a biological entity (plant or animal) takes an active part in the carbon cycle and it contains the same proportion of the isotope as the atmosphere does (about one ten millionth of the carbon is carbon14). The death of an organism terminates the incorporation of this isotope into the fabric of the entity. From the time of death onwards the proportion of carbon14 in the dead orgamism decreases as it decays into nitrogen.
By calculating the ratio of C14 to total carbon in a sample of the artefact it is possible to work out its age. The halflife of carbon14 is 5,600 years. E.g.

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