Pushing the precision limit of (super 14) C AMS.

Abstract

High precision for radiocarbon cannot be reached without profound insight into the various sources of uncertainty which only can be obtained from systematic investigations. In this paper, we present a whole series of investigations where in some cases (super 16) O: (super 17) O: (super 18) O served as a substitute for (super 12) C: (super 13) C: (super 14) C. This circumvents the disadvantages of event counting, providing more precise results in a much shorter time. As expected, not a single effect but a combination of many effects of similar importance were found to be limiting the precision. We will discuss the influence of machine tuning and stability, isotope fractionation, beam current, space charge effects, sputter target geometry, and cratering. Refined measurement and data evaluation procedures allow one to overcome several of these limitations. Systematic measurements on FIRI-D wood show that a measurement precision of + or -20 (super 14) C yr (1 sigma ) can be achieved for single-sputter targets.