EXPLORING SAMPLE SIZE LIMITS OF AMS GAS ION SOURCE C-14 ANALYSIS AT COLOGNEAMS

摘要

Increasing demands for small-scale radiocarbon (C-14) analyses required the installation of a "SO-110 B" type ion source (HVE Europa B.V.) at our 6 MV Tandetron AMS (HVE) dedicated for the direct injection of CO2 using either the gas injection system (GIS) from Ionplus AG or a EuroVector EA 3000 elemental analyzer (EA). We tested both systems with multiple series of C-14-free and modern standards (2.5-50 mu g C) combusted in quartz ampoules or EA containers and were able to quantify exogenous C introduced. In EA-GIS-AMS analysis exogenous C is mainly derived from the EA sample containers. Blank values for 50 mu g C combusted in solvent-cleaned tin (Sn) vessels were 0.0127 +/- 0.0012 (FC)-C-14 (boats) and 0.0090 +/- 0.0010 (FC)-C-14 (capsules), while they were much higher for thermally cleaned silver (Ag) capsules. The processing of gas samples for GIS-AMS yields similar blank values corresponding to 0.30 +/- 0.08 mu g exogenous C with 0.93 +/- 0.23 (FC)-C-14 consisting of 0.28 mu g C modern and 0.02 mu g C fossil C. The combustion of larger amounts of blank material (1 mg C) in a single quartz tube split into aliquots gives lower blanks (0.0064 +/- 0.0008 (FC)-C-14; 50 mu g C). Thus, C-14 analysis of small, gaseous samples is now possible at CologneAMS.