Primary and secondary standards are essential in radiocarbon analyses for the purpose of reporting and comparing data among laboratories, as well as for internal laboratory data quality control. ANU sucrose is one of the IAEA-certified 14C standards (C-6) with a consensus value of 1.5061 ± 0.0011 fraction modern (Fm). All of our measurements of ANU sucrose (n = 351) as a secondary standard over the last 7 yr result in an average value of 1.5016 ± 0.0005 Fm (2-σ standard error). After applying the same outlier tests used for IAEA reference standards, a weighted average value of 1.5016 ± 0.0002 Fm (n = 294) was calculated. This value is significantly lower than the IAEA C-6 consensus value (t test with unequal variance; p = 0.023). In contrast, our measurements of other secondary standards over the same time period are in excellent agreement with their respective consensus values. Since ANU is the only secondary standard measured in our lab that does not agree with the consensus values, and we have measured a larger number analyses compared to what went into the definition of the consensus value, we suggest that the consensus value of ANU sucrose might be too high by ~0.0045 ± 0.0011 Fm. Given that some labs routinely use ANU sucrose as a primary standard, our results suggest that revisiting the consensus value of ANU sucrose may be necessary.

A new 14C accelerator mass spectrometry (AMS) laboratory for carbon cycle studies has been established at the University of California, Irvine. The 0.5 MV AMS system was installed in mid-2002 and has operated routinely since

October of that year. This paper briefly describes the spectrometer and summarizes lessons learned during the first year of operation. In the process of setting up the system, we identified and largely suppressed a previously unreported radiocarbon

AMS background: charge exchange tails from 14N beams derived from nitrogen-containing molecular ions produced near the entrance of the accelerator.