Mass spectrometry with accelerators

• Published in: Mass spectrometry reviews 2011-11, Vol.30 (6), p.1037-1072
• Main Authors: Litherland, A. E., Zhao, X-L., Kieser, W. E.
• Format: Article
• Language: English
• Subjects: accelerator mass spectrometry (AMS); accelerators; Anions; Canadian contributions; chemical reaction cells; Chemistry; Dating; Exact sciences and technology; Inorganic chemistry and origins of life; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Ion currents; Ions; isobars; Isotopes; Isotopes and labelled compounds chemistry; Mass spectrometers and related techniques; Mass spectrometry; Mass spectroscopy; nuclear physics techniques; Physics; Preparations and properties; Radiocarbon dating; radioisotopes; Scientific imaging; stable isotopes; tandem accelerator
• ISSN: 0277-7037; 1098-2787
• DOI: 10.1002/mas.20311

As one in a series of articles on Canadian contributions to mass spectrometry, this review begins with an outline of the history of accelerator mass spectrometry (AMS), noting roles played by researchers at three Canadian AMS laboratories. After a description of the unique features of AMS, three examples, 14C, 10Be, and 129I are given to illustrate the methods. The capabilities of mass spectrometry have been extended by the addition of atomic isobar selection, molecular isobar attenuation, further ion acceleration, followed by ion detection and ion identification at essentially zero dark current or ion flux. This has been accomplished by exploiting the techniques and accelerators of atomic and nuclear physics. In 1939, the first principles of AMS were established using a cyclotron. In 1977 the selection of isobars in the ion source was established when it was shown that the 14N− ion was very unstable, or extremely difficult to create, making a tandem electrostatic accelerator highly suitable for assisting the mass spectrometric measurement of the rare long‐lived radioactive isotope 14C in the environment. This observation, together with the large attenuation of the molecular isobars 13CH− and 12CH 2− during tandem acceleration and the observed very low background contamination from the ion source, was found to facilitate the mass spectrometry of 14C to at least a level of 14C/C ∼ 6 × 10−16, the equivalent of a radiocarbon age of 60,000 years. Tandem Accelerator Mass Spectrometry, or AMS, has now made possible the accurate radiocarbon dating of milligram‐sized carbon samples by ion counting as well as dating and tracing with many other long‐lived radioactive isotopes such as 10Be, 26Al, 36Cl, and 129I. The difficulty of obtaining large anion currents with low electron affinities and the difficulties of isobar separation, especially for the heavier mass ions, has prompted the use of molecular anions and the search for alternative methods of isobar separation. These techniques are discussed in the latter part of the review. © 2010 Wiley Periodicals, Inc., Mass Spec Rev 30:1037–1072, 2011