Carbonate as sputter target material for rapid C-14 AMS

TitleCarbonate as sputter target material for rapid C-14 AMS
Publication TypeJournal Article
Year of Publication2013
AuthorsLongworth, BE, Robinson, LF, Roberts, ML, Beaupré, SR, Burke, A, Jenkins, WJ
JournalNuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms

This paper describes a technique for measuring the C-14 content of carbonate samples by producing C- ions directly in the negative ion sputter source of an accelerator mass spectrometer CAMS) system. This direct analysis of carbonate material eliminates the time and expense of graphite preparation. Powdered carbonate is mixed with titanium powder, loaded into a target cartridge, and compressed. Beam currents for optimally-sized carbonate targets (0.09-0.15 mg C) are typically 10-20% of those produced by optimally-sized graphite targets (0.5-1 mg C). Modern (>0.8 Fm) samples run by this method have standard deviations of 0.009 Fm or less, and near-modern samples run as unknowns agree with values from traditional hydrolysis/graphite to better than 2%. Targets with as little as 0.06 mg carbonate produce useable ion currents and results, albeit with increased error and larger blank. In its current state, direct sputtering is best applied to problems where a large number of analyses with lower precision are required. These applications could include age surveys of deep-sea corals for determination of historic population dynamics, to identify samples that would benefit from high precision analysis, and for growth rate studies of organisms forming carbonate skeletons. (C) 2012 Elsevier B.V. All rights reserved.