• Priller, Alfred
• Mair, Klaus
• Wild, Eva Maria
• Vonderhaid, Iris
• Steier, Peter
• Liebl, Jakob
• Kutschera, Walter
• Golser, Robin

Abstract

For C-14 AMS measurements of samples at the microgram level, ion source related effects start to play a role, while generally the lower sample size limit is set by the carbon background introduced during chemical preparation procedures. Measurements of about 800 graphite targets in the mass range of 1-100 mu g were performed within 25 AMS beam-times during the last three years at VERA, revealing a dependency of measured C-14(3+)/C-12(3+) ratios on C-12(3+) currents. This dependency can be accounted for by assuming a background current, which was determined for each AMS measurement by least square fitting. C-12(-) ion currents extracted from microgram graphite samples were typically (1.0 +/- 0.5) mu A / mu g C. On average a C-12(3+) background current of (0.14 +/- 0.14) mu A with (FC)-C-14 = 0.22 +/- 0.46 (skewness gamma(1) = 3.0) was deduced with significant variations between single measurements. The determination of this background current for each AMS measurement of microgram graphite samples allowed to apply a quantitative correction and thereby to improve the AMS measurement precision. Furthermore, the yield of graphitization and ionization in a Cs sputter ion source of graphitized microgram CO2 samples was investigated. No dependency on the cathode target geometry was observed for 9 differently shaped cathode types.

Topics

• impedance spectroscopy
• Carbon
• additive manufacturing
• Accelerator mass spectrometry