Thursday, 8 September 2005

This presentation is part of: Poster Session II

Use of Natural Diamonds to Monitor Radiocarbon AMS Instrument Backgrounds

R. E. Taylor, Department of Anthropology, University of California, Riverside, Riverside, CA 92521 and John Southon, Keck Carbon Cycle Accelerator Mass Spectrometry Laboratory, University of California, Irvine, Irvine, CA 92697.


The initial anticipation that AMS-based systems might achieve 14C-inferred age measurements of of 105 years (~ 0.000004 fraction modern [fm]) has been, to date, unrealized due to a variety of sample processing and instrument-based experimental constraints. To examine instrument-based backgrounds in the University of California Keck Carbon Cycle AMS spectrometer, we have obtained measurements on a set of natural diamonds physically mounted in cathodes. Natural diamond samples (N=14) from different sources within rock formations with geological ages in excess of 100 my, yielded a range of currents (~110 to 250 μA 12C- where filamentous graphite typically yields ~150 μA 12C- ) and apparent 14C ages (64,920±430 BP [0.00031±0.00002 fm] to 80,000±1100 BP [0.00005±0.00001 fm] ). Six fragments cut from a single diamond exhibited very similar 14C values—69,380±550 to 70,600±560 BP.  The oldest 14C age equivalents were measured on a natural diamonds which exhibited the highest current yields. 


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See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)