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