Quality Control

14Chrono Centre is commited to continual quality assurance/control checks to ensure that the high standards of reproducibility, precision and accuracy on our 14C dates are maintained.

This is largely achieved through participation in international laboratory intercomparison programs and the routine analysis of a suite of reference materials (a comprehensive description of our quality assurance/control is provided below).

International Radiocarbon Intercomparison

The international radiocarbon intercomparison is a long-running program of inter-laboratory quality control exercises undertaken by the 14C community (e.g. TIRI, FIRI, VIRI, SIRI, Scott 2003; Scott et al. 2010a, 2010b, 2017). 14CHRONO actively participates in these programs and has analysed and reported results for both VIRI and SIRI, as well as using standards from earlier intercomparisons as a part of our routine analysis program.

Figure 1: Comparison of 14CHRONO and consensus F14C values from the Sixth International Radiocarbon Intercomparison (SIRI)

Figure 1

Table 1

For the most recent intercomparison, SIRI (Sixth International Radiocarbon Intercomparison, 2013-2017, Scott et al. 2017.

13 samples were sourced and distributed to AMS laboratories from which more than 40 reported results. The results from 14CHRONO are in excellent agreement with the consensus values reported across all laboratories.

Table 1: Accuracy and precision from most recent international radiocarbon intercomparision (SIRI) samples. Samples were treated as unknowns so background corrections were made to all samples. (c) is infinite age, (nc) is finite age.

Routine Analysis of Reference Material

Every wheel of samples we run on the AMS contains a minimum of 4 secondary standards. Typically, these secondaries consist of 2 pairs of samples taken from a larger set of standards with internationally agreed upon consensus values (e.g. TIRI/FIRI standards, see Table 2).

As well as that, there are standards for which a long series of measurements on our accelerator have been built up; for example a pair of ANU sucrose ((IAEA-C6) standards have been included in almost every wheel run on the AMS since the machine was commissioned, thus providing us with a large data series of over 1800 measurements.

This allows us to monitor the short term as well as long term precision, accuracy and repeatability of our radiocarbon dates ensuring any degradation in performance is both recognized and resolved swiftly.

Table 2

Table 2: Accuracy, precision and laboratory error multiplier of the main secondary standards and backgrounds analysed since 2012. Background values are not corrected.

Table 3

Precision of Dates

Together with maintaining excellent accuracy in our results, we are equally committed to ensuring high standards of precision for our reported dates. The expected average precision achievable for different sample types and for various timescales is provided in Table 3.

Table 3: Expected average precision achievable (for each sample type with regard to the timescales) and number of samples (n) included in average (based on unknowns analysed 2012-2017)

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History

The Centre provides radiocarbon (14C) dates and stable isotope analysis as well as statistical chronological...