Fundamentals of accelerator mass spectrometry

Abstract

The extension of high-sensitivity mass spectrometry to isotope ratios in the range 10 -12 - 10 -15 has been called accelerator mass spectrometry (AMS) because of the use of an additional stage of acceleration that facilitates the removal of molecular interferences and the separation of isobars. In some cases the ultra-high sensitivity is obtained by exploiting the instability of the negative ion of the interfering isobar. It is now possible to measure such isotopes as 14 C at natural abundances as low as one atom in 10 +15 12 C atoms. The ideas behind this significant extension of mass spectrometric techniques will be discussed.

Quantifying absolute carbon isotope ratios by AMS

“…The cross-section for CH + projectile energies (heavy solid line) is nearly constant to very low energy. The He (5) and N 2 (4) r 11 of CH + measured in [46] support the calculated magnitude of this cross-section. …”

“…The data further imply that our sputter ion source produces carbon anions that are free of the universally assumed isotope fractionations expected from surface ionization [5][6][7]. We attribute this to a neutral resonant ionization of the copious sputtered sample atoms [8] within a cloud of metastable Cs atoms [9] that evaporate from the sample and holder by the heat of the primary Cs+ beam.…”

Bioanalytical Applications of Accelerator Mass Spectrometry for Pharmaceutical Research

“…The rare ions of interest are detected at rates of a few thousand counts per second to a few seconds per count (equivalent to an ion "current" of ≤ 1 femtoAmp). More detailed discussion of the principals behind the high sensitivity of AMS for rare isotopes can be found in several reviews [6,[47][48][49].…”

Anion formation by neutral resonant ionization

“…A theory of CSIS ionization is widespread [9,10], based on the work of Nørskov and Lundqvist explaining the surface ionization of samples in negative secondary ionization mass spectrometry (SIMS) [11]. However, SIMS and a CSIS have large differences in analytical practice.…”