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The radiocarbon (14C) calibration curve so far contains annually resolved data only for a short period of time. With accelerator mass spectrometry (AMS) matching the precision of decay counting, it is now possible to efficiently produce large datasets of annual resolution for calibration purposes using small amounts of wood. The radiocarbon intercomparison on single-year tree-ring samples presented here is the first to investigate specifically possible offsets between AMS laboratories at high precision. The results show that AMS laboratories are capable of measuring samples of Holocene age with an accuracy and precision that is comparable or even goes beyond what is possible with decay counting, even though they require a thousand times less wood. It also shows that not all AMS laboratories always produce results that are consistent with their stated uncertainties. The long-term benefits of studies of this kind are more accurate radiocarbon measurements with, in the future, better quantified uncertainties. [ABSTRACT FROM AUTHOR]

The New Oxalic Acid standard (NOX) was introduced in 1980 to replace the primarily Oxalic Acid (OX) standard, which was calibrated against OX utilizing decay counting measurements. However today, most radiocarbon measurements are performed with accelerator mass spectrometry that is more powerful as significantly less material is required and the measurement time is reduced. Here we give an update on the calibration of the NOX against OX. Over 500 radiocarbon measurements on either OX or NOX were compiled to an exact calibration, that outperforms the original calibration in precision. Our measurements are in agreement with the first measurements performed in the 80's, demonstrating that AMS is capable of reproducing highest precision radiocarbon measurements on a routine basis. [ABSTRACT FROM AUTHOR]