The CAIS radiocarbon AMS facility houses two AMS units. The 500 kV NEC 1.5SDH-1 pelletron (CAMS) is a tandem accelerator equipped with a 134-cathode MC-SNICS negative ion source. During the AMS measurement, negative ions of carbon isotopes 12C, 13C and 14C are sequentially injected and accelerated towards the positive high voltage terminal. At the terminal, the negative ions undergo charge exchange collisions with argon gas atoms and become positive ions. The repulsion between the positive ions and the terminal causes further acceleration of the ions to a total energy of 1 MeV. After acceleration, each isotope is mass separated by magnetic field. 12C and 13C beams are measured in Faraday cups whereas the rare isotope 14C is measured using a particle detector.
The 250 kV NEC Single Stage AMS (SSAMS) is also equipped with the 134-cathode MC-SNICS ion source. SSAMS unit does not have a second stage acceleration, and the total beam energy is about 300 keV. This unit has a lower beam transmission compared to the CAMS unit, so it takes longer measurement time to achieve the same precision as that of CAMS. However, SSAMS unit requires much less maintenance than CAMS.