Future needs and requirements for AMS ¹⁴C standards and reference materials

¹⁴C measurement uses a number of standards and reference materials with different properties. Historically the absolute calibration of ¹⁴C measurement was tied to 1890 wood, through the 'primary' standard of NBS-OxI (produced by the National Bureau of Standards, now NIST - National Institute of Standards and technology) subsequently replaced by NBS-OxII. These are both internationally calibrated and certified materials, whose ¹⁴C activities are known absolutely. A second tier of materials, often called secondary standards or reference materials, and including internationally recognised materials such as ANU-sucrose (now also IAEA-C6), Chinese - sucrose and the IAEA C1-C6 series, augmented by additional oxalic acid samples are also used routinely. The activity of these materials has been estimated from large numbers of measurements made by many laboratories. Recently, further natural materials from the Third and Fourth International Radiocarbon Inter-comparisons (TIRI and FIRI) have been added to this list. The activities of these standards and reference materials span both the applied ¹⁴C age range and the chemical composition range of typical samples, but this is not achieved uniformly and there is a continuing need for reference materials for laboratory quality control and measurement-traceability purposes. In this paper, we review the development of ¹⁴C standards and reference materials and consider the future requirements for such materials within the ¹⁴C AMS community.