Monday, 5 September 2005 - 10:50 AM

This presentation is part of: Ion Sourcery (optics, modeling, performance, etc)

Progress on a Gas Ion Source for Continuous-Flow Accelerator Mass Spectrometry

Mark Roberts, R.J. Schneider, K.F. Von Reden, B.X. Han, and J.M. Hayes. National Ocean Sciences AMS Facility, Woods Hole Oceanographic Institution, Mail Stop #8, Woods Hole, MA 02543

The National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility at Woods Hole Oceanographic Institution is constructing a system for the analysis of 14C in a continuously flowing stream of carrier gas.

A key component of the system will be a gas-accepting ion source. The source is a microwave-plasma source first built at Atomic Energy of Canada Limited, Chalk River, Ontario, Canada and subsequently developed at NOSAMS[1,2]. The source uses 2.45 GHz microwaves and a continuously flowing mixture of argon and carbon dioxide to sustain a plasma. Positive ions are extracted from the source and converted to negative ions by passage through a magnesium-vapor charge-exchange canal located at the exit of the ion source.

The microwave plasma source will be connected to a compact Accelerator Mass Spectrometry (AMS) system that is currently being constructed. The system is optimized in design for the gas-accepting ion source and is being constructed from a mixture of vendor-supplied and in-house-designed components. Precision of the system will vary directly with the square root of the fraction of modern of a sample and inversely with square root of sample size. Based on demonstrated levels of performance of the ion source and recent experience with small AMS systems at other institutions, we expect the standard deviation of a single measurement of the fraction of modern carbon in a sample containing one microgram of carbon will be 70 per mil at Fm=0.5.

Data from the gas ion source along with design details of the spectrometer will be presented. The earliest users of the system will be marine geochemists, microbial ecologists, environmental chemists, and atmospheric chemists.

[1] Wills J.S.C., Lewis R.A., Diserens J., Schmeing H. and Taylor T., ‘A compact high-current microwave-driven ion source', Rev. Sci. Instrum. 69, 65-68.

[2] Schneider R.J., Kim S. -W., von Reden K.F., Hayes J.M., Wills J.S.C, Griffin, V.S., Sessions, A.L., and Sylva, S., ‘A gas ion source for continuous-flow AMS'. Nucl. Instr. and Meth. in Phys. Res., B223-224, 149-154.



Web Page: www.nosams.whoi.edu/research/research_gasion.htm

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