A New Technology for Elimination of Isobaric Interferences in Ultra-Sensitive Isotope Measurements
Abstract
Accelerator Mass Spectrometry (AMS) is a technique used for ultra-sensitive abundance ratio measurements. Applications in the earth sciences typically involve the measurement of 10Be, 14C, 26Al, 36Cl, 41Ca and 129I, for example in exposure dating and ground water studies, sometimes yielding ratios of unstable to stable isotope at 10-15 or less. AMS is most effective when the stable atomic isobar does not form a stable negative ion. When this is not the case larger accelerators have been required. Here we report preliminary tests of a prototype radio-frequency quadrupole collision cell system for the removal of isobaric interferences for Accelerator Mass Spectrometry (AMS) and for studies of anion-gas interactions at low energy. A fully developed ISA could allow smaller AMS systems to handle a wider range of samples. This system, known as an Isobar Separator for Anions (ISA), decelerates a mass-analyzed beam of anions from an energy typically generated by an AMS ion source (∼20 keV) down to < 10 eV. Radiofrequency quardrupoles and electrostatic lenses then guide the ions through the collision cell where ion-gas reactions attenuate most of the unwanted isobars and ion-gas elastic collisions reduce the ion energy and energy spread of the ion beam (cool the ions). The anions are then reaccelerated to their original energy for injection into the rest of the AMS system. With the ISA installed on a full 3MV AMS system, attenuations of 32S-, 12C3-, and 39K- by six, seven, and > ten orders of magnitude respectively have been achieved using NO2 gas in the collision cell. Transmission of a non-reactive anion is approximately 10-20% through the ISA. Further measurements of four 36Cl standards (4 x 10-13 < 36Cl/Cl < 4 x 10-11) and an estimate of the attenuation of the interfering isobars 36S-and 12C3-is also described.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2009
- Bibcode:
- 2009AGUSM.A11C..09E
- Keywords:
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- 1040 Radiogenic isotope geochemistry;
- 1065 Major and trace element geochemistry;
- 1094 Instruments and techniques;
- 1115 Radioisotope geochronology;
- 1150 Cosmogenic-nuclide exposure dating (4918)