other binaries, are only broken at MeV energies, rather than the keV energies normally used in standard isotope-ratio mass spectrometry.

In the 10 MeV AMS system in use at CAMS, small samples of biological origin are introduced to the spectrometer after being combusted to carbon dioxide and reduced to graphite. A schematic of the system is shown in Figure 13.15. Carbon atoms and molecular isobars are subsequently ionized and accelerated toward a positive potential of 6.5 MeV in a tandem Van der Graff accelerator. These 7 MeV negative ions collide with a thin foil within the accelerator to lose five electrons and become positively charged. Molecular ions (i.e., 12,13CH) do not survive at this charge state and are thus eliminated as interfering isobars. The 4+ ion then obtains an additional 4 x 7 MeV in accelerating away from the high-potential collision cell to become a 35 MeV 14C4+


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