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IMPROVING IONPLUS MICADAS PERFORMANCE WITH RECESSED GRAPHITE

Published online by Cambridge University Press:  04 April 2024

Taylor A B Broek*
Affiliation:
National Ocean Sciences Accelerator Mass Spectrometry Facility, Woods Hole Oceanographic Institution, 266 Woods Hole Rd., Woods Hole, MA, USA
Mark L Roberts
Affiliation:
National Ocean Sciences Accelerator Mass Spectrometry Facility, Woods Hole Oceanographic Institution, 266 Woods Hole Rd., Woods Hole, MA, USA
*
*Corresponding author. Email: taylor.broek@whoi.edu

Abstract

Cathodes with recessed sample surfaces have several benefits in cesium sputter ion sources, including higher output, more efficient use of sample material, and improved focusing of the extracted ion beam. However, the Ionplus MICADAS uses cathodes with a graphite surface that is essentially flush with the sample holder. To evaluate the performance of recessed graphite with the MICADAS and determine the optimal surface depth, we tested four different depths, including the standard (flush) pressing method, 0.5 mm, 1.0 mm, and 1.5 mm. We found that recessed depths of 1.0 and 1.5 mm resulted in 20% higher ion beam current compared to the standard method under the same source conditions. The results are consistent with the beam produced from the recessed targets being more narrowly focused with a lower emittance, resulting in better transmission through the accelerator. Small graphite samples (200 µg C) with recessed surfaces produced higher currents for longer, leading to a 2–3× increase in sample ionization efficiency. Additionally, there was some evidence that isotopic ratio measurements of recessed samples were more stable over time. Overall, samples recessed to 1 mm depth offered numerous advantages over the standard pressing method and we have subsequently started pressing all MICADAS graphite using this approach.

Type
Conference Paper
Copyright
© Woods Hole Oceanographic Institution, 2024. Published by Cambridge University Press on behalf of University of Arizona

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Footnotes

Selected Papers from the 24th Radiocarbon and 10th Radiocarbon & Archaeology International Conferences, Zurich, Switzerland, 11–16 Sept. 2022.

References

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