What is AMS?
Accelerator Mass Spectrometry (AMS) is a method which combines the principles of mass spectrometry and the tandem accelerator, to measure isotope ratios by accurately counting the extremely small
number of rare isotope particles in the sample.
The mass spectrometry method utilizes the difference of orbit between ions with different mass within a magnetic field. Thus it is difficult to mutually discriminate between ions with the same mass number. For example, when measuring 14C, a radio isotope of carbon, nitrogen ions with the same mass number(14N) and 13CH, a stable isotope of carbon, 13C, bonded with hydrogen, gets into the way. In AMS, as shown in the figure,
1) in producing the negatively charged ions, the ionization of the interfering
element (nitrogen), with no electron affinity, is restrained. 2) The electrons
are stripped off and the molecular ions are destroyed on collision with
the charge exchange canal in the terminal. 3) Furthermore, by discriminating
each of the isotopes/elements in the high energy ion detector the interference
is completely avoided. Thus, it is possible to accurately measure long
lived radio isotopes (14C, 10Be, 26AI, 36CL, 4lCa, 129I, etc.) produced by cosmic rays.