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IGERT program in Archeological Science

Principles of AMS

Radiocarbon dating





Age Calculation


Cosmogenic Radioisotopes



    After the graphitization process, the graphite powder (~0.5mg) samples are packed into target holders and mounted in the target wheel (holding 32 or 40 targets), which is inserted into the accelerator ion source. Eight to ten standard graphite targets, made from oxalic acid standards I (crop of 1955 sugar beet) and II (crop of 1977 French beet molasses) produced by the U.S. National Institute of Standards and Technology, are run in each wheel. Later the results are calculated by comparison of the 14C content of the samples to these two standards and normalization to "modern" 1950 AD.

    The physics describing a carbon-14 particle passing through the accelerator mass spectrometer is discussed in the principles of ams page. To measure the amount of carbon-14, we use a silicon surface barrier detector (As shown in the diagram below). The beam passes through a mylar foil at the entrance of the detector. Carbon-14 and nitrogen-14 particles lose energy at different rates when they pass through the mylar foil. This allows the detector to resolve the two isobars.