Determination of chlorine concentrations in whole rock: Comparison between prompt-gamma activation and isotope-dilution AMS analysis

• Published in: Quaternary geochronology 2009-12, Vol.4 (6), p.501-507
• Main Authors: Di Nicola, L., Schnabel, C., Wilcken, K.M., Gméling, K.
• Format: Article
• Language: English
• Subjects: Chlorine; Chlorine-36; Isotope-dilution AMS; Prompt-gamma activation analysis
• ISSN: 1871-1014; 1878-0350
• DOI: 10.1016/j.quageo.2009.08.001

Accurate determination of chlorine concentrations in terrestrial rocks is of importance for the interpretation of terrestrial in-situ cosmogenic 36Cl. Neutron capture by 35Cl, together with production from Ca and K, is one of the three major production pathways of 36Cl in rocks. Here, we present an inter-comparison of chlorine determinations by two procedures. The first approach is an independent Cl determination by prompt-gamma (neutron) activation analysis (PGAA). The second method is isotope-dilution based on isotopically enriched stable chlorine carrier added during chemical sample preparation for accelerator mass spectrometry (ID-AMS). Twenty-six (26) whole rock samples have been processed for PGAA and ID-AMS analysis. This study constitutes the first published inter-comparison for concentrations below 100 μgCl/g. Our results show no significant difference in Cl concentrations between methods. This agreement indicates good retention of chloride during the procedure we employ for whole rock sample dissolution. No significant loss of stable chlorine from either the spike or the sample occurs before isotopic equilibrium is reached, prior to AgCl precipitation. Uncertainties, which are