JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY JAMES KING-HOLMES / SCIENCE PHOTO LIBRARY
A section of the accelerator mass spectrometer (AMS) in the Oxford Radiocarbon Accelerator Unit for determination of the dates of samples of organic material. In the foreground is a beam-bending magnet incorporating the recombinator section, which uses Faraday cups (operated by the vertical rods) to help separate the beams of ionised carbon-12, 13 and 14. Because carbon contains only 1 atom of the carbon-14 isotope in 1, 000, 000, 000, 000 of the more stable carbon-12 and carbon-13, most of the carbon-12 atoms are discarded and the streams of ions are directed and accelerated along the machine which converts the negatively charged ions to a positive charge and uses other filters to allow the only carbon-14 ions to be counted by a detector at the end of the accelerator.
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