Japan Geoscience Union Meeting 2025

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[J] Oral

M (Multidisciplinary and Interdisciplinary) » M-ZZ Others

[M-ZZ42] Frontiers in geochemistry: new challenges and future prospects

Fri. May 30, 2025 3:30 PM - 5:00 PM 103 (International Conference Hall, Makuhari Messe)

convener:Hajime Obata(Marine inorganic chemistry division, Atmosphere and Ocean Research Institute, University of Tokyo), Makiko K. Haba(Department of Earth and Planetary Sciences, Tokyo Institute of Technology), Hirochika Sumino(Research Center for Advanced Science and Technology, The University of Tokyo), Mayuri Inoue(Department of Earth Sciences, Okayama University), Chairperson:Hajime Obata(Marine inorganic chemistry division, Atmosphere and Ocean Research Institute, University of Tokyo), Makiko K. Haba(Department of Earth and Planetary Sciences, Tokyo Institute of Technology), Hirochika Sumino(Research Center for Advanced Science and Technology, The University of Tokyo), Mayuri Inoue(Department of Earth Sciences, Okayama University)

3:45 PM - 4:00 PM

[MZZ42-07] Future prospects for AMS measurements of cosmogenic nuclides via understanding the mechanism of negative ion formation in Cs-sputter ion sources

*Atsunori Nakamura1, Takeyasu Yamagata2, Hiroyuki Matsuzaki2 (1.National Institute of Advanced Industrial Science and Technology, 2.The University of Tokyo)

Keywords:cosmogenic nuclides , accelerator mass spectrometry, ionization, Cs-sputter ion source

Cosmogenic nuclides have been used in a wide variety of geologic studies. In particular, cosmogenic 10Be is a useful tool to provide ages of surface exposure. When measuring cosmogenic nuclides using accelerator mass spectrometry (AMS), obtaining higher negative ion beam currents from Cs-sputtered samples is the key for precision, because higher beam currents provide larger counts of the target nuclides and are thereby directly linked to counting statistics (Nakamura et al., 2021). However, the mechanism of negative ion formation in Cs-sputter ion sources is still under discussion. Recent studies propose that negative ions are produced in a Cs-sputter ion source via resonant electron transfer (Vogel, 2015). The model predicts that BeO- currents are affected by the choice of cathode material because competitive ionization occurs between BeO and the cathodes. In this presentation, we discuss the findings from the experiments to determine the effect of cathode materials on BeO- currents for AMS measurements (Nakamura et al., 2025). The peak currents of stainless-steel cathodes were higher than those of Cu cathodes, indicating the benefits of using stainless-steel cathodes for measuring low-level samples. In the first approximation, the difference in the peak BeO- currents between the Cu and stainless-steel cathodes can be explained by the difference in the electron affinities of the cathode component metals. Further insights into the mechanism of competitive ionization were provided by considering the energy levels of excited neutral Cs (Nakamura et al., 2025). The findings are not limited to optimize 10Be measurements, but applicable to AMS measurements for better negative ion formation. Moreover, the theory for resonant electron transfer benefit wide range of studies conducted using Cs-sputter ion sources.

Nakamura et al., 2021, Geochemical Journal 55, 209–222.
Nakamura et al., 2025, NIMB 558, 165562.
Vogel., 2015, NIMB 361, 156–162.