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MODEL RELEASED. Accelerator mass spectrometer (AMS) used for carbon dating. The AMS converts atoms from a sample into a beam of ions, which are accelerated along this tube, the linear accelerator. It then measures the mass of the ions by the application of electric and magnetic fields. All living material incorporates a radioactive isotope of carbon, carbon-14 (14C), and a stable isotope, carbon-12 (12C), into its tissue at a known ratio. When the tissue dies the amount of 12C remains constant, but 14C decays. Measuring the amount of 14C compared to 12C in a sample indicates how long ago the tissue died. Photographed at Oxford Radiocarbon Accelerator Unit, University of Oxford, UK.