Atom counting with accelerator mass spectrometry

Accelerator mass spectrometry (AMS) is a mass-spectrometric method using entire accelerator systems to measure ultralow traces of long-lived radioisotopes. AMS spectrometers produce an ion beam from a sample of interest and separate ions according to their magnetic, electric, and atomic characteristics. It is thus possible to identify both the mass number and the atomic number of a very rare radioisotope, and count it atom by atom. The review describes the 45-year history since the discovery of AMS, detailed technical aspects, and a wide range of research fields.