The potential for AMS analysis of 10Be using BeF−
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Isobar
Accelerator mass spectrometry
Metastability
Preliminary tests of a prototype radio‐frequency quadrupole (RFQ) collision cell system, known as an isobar separator for anions (ISA), for the removal of isobaric interferences for accelerator mass spectrometry (AMS) and for studies of anion–gas interactions are reported. The ISA decelerated a mass‐analysed beam of anions from an energy (∼ 20 keV) typically generated by an AMS ion source to < 10 eV. RFQs and electrostatic lenses then guided the ions through the collision cell where ion‐gas collisions reduced both the energy and energy spread of the ion beam (cooled the ions) and ion‐gas reactions attenuated most of the unwanted isobars. The anions were then re‐accelerated to their original energy for injection into the rest of the AMS system. With the ISA installed on a full 3 MV AMS system, attenuations of 32 S ‐ , 12 C 3 ‐ and 39 K ‐ by six, seven and greater than ten orders of magnitude, respectively were achieved using 0.7–1 Pa NO 2 gas in the collision cell, while maintaining approximately 10–30% of the chlorine anion transmission. A further measurement of a 36 Cl/Cl = 4.1 × 10 ‐11 RM is also described. The results suggest that the 36 Cl/Cl lower detection limit of the current system was 10 ‐14 –10 ‐15 for samples that could be prepared with S/Cl ratios below 10 μg g ‐1 .
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Accelerator mass spectrometry
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Quadrupole mass analyzer
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Accelerator mass spectrometry
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Tandem accelerator
Isobaric process
Nuclide
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Accelerator mass spectrometry
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Two new techniques, which extend the range of elements that can be analyzed by Accelerator Mass Spectrometry (AMS), and which increase its isobar selection capabilities, have been recently introduced. The first consists of embedding the sample material in a fluoride matrix (e.g. PbF2), which facilitates the production, in the ion source, of fluoride molecular anions that include the isotope of interest. In addition to forming anions with large electron binding energies and thereby increasing the range of analysable elements, in many cases by selection of a molecular form with a particular number of fluorine atoms, some isobar discrimination can be obtained. The second technique, for the significant reduction of atomic isobar interferences, is used following mass selection of the rare isotope. It consists of the deceleration, cooling and reaction of the rare mass beam with a gas, selected so that unwanted isobars are greatly attenuated in comparison with the isotope of interest. Proof of principle measurements for the analysis of 36C1 and 41Ca have provided encouraging results and work is proceeding on the integration of these techniques in a new AMS system planned for installation in late 2012 at the University of Ottawa.
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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.
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