JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY
Carbon dating. Scientist holding a phial containing a sample for carbon dating using accelerator mass spectrometry (AMS). 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. Carbon dating using AMS needs only a very small sample of material, minimising the damage to a specimen. Samples must be protected against contamination from material of a different age. Photographed at Oxford Radiocarbon Accelerator Unit, University of Oxford, UK.
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