JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY
Accelerator mass spectrometer (AMS) used for carbon dating. The AMS converts atoms from a sample into a beam of ions. The mass of the ions is then measured using electric and magnetic filters (silver and black, round, left). 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.
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