International Radiocarbon Intercomparison

International Radiocarbon Intercomparison
Name	International Radiocarbon Intercomparison
Date	Late 1980s – 1990s
Location	Coordinated from the University of Glasgow
Participants	Over 100 laboratories globally
Field	Radiocarbon dating, Archaeology, Quaternary science
Organizer	Gordon T. Cook, University of Glasgow

International Radiocarbon Intercomparison. The International Radiocarbon Intercomparison was a pivotal, large-scale scientific exercise designed to assess and improve the comparability and reliability of radiocarbon dating results produced by laboratories worldwide. Organized primarily from the University of Glasgow under the leadership of Gordon T. Cook, it involved the coordinated analysis of standardized sample materials by a vast network of participating facilities. This systematic effort was crucial for validating the accuracy of dates used in fields like archaeology and palaeoclimatology, ultimately leading to enhanced quality assurance protocols across the discipline.

Background and Purpose

The need for a comprehensive intercomparison arose from the growing application of radiocarbon dating to critical research in Quaternary geology, archaeological chronology, and studies of climate change. Prior to the 1980s, individual laboratories calibrated their results using standards like Oxalic Acid from the National Institute of Standards and Technology, but there was no widespread mechanism to compare routine performance. Discrepancies in reported ages for the same material could undermine major scientific syntheses, such as those concerning the Younger Dryas or the Neolithic Revolution. The primary purpose was therefore to establish a baseline of laboratory performance, identify sources of inter-laboratory variation, and promote the adoption of consistent, high-quality measurement practices on a global scale.

Methodology and Design

The exercise was meticulously designed as a series of progressive stages. Participants were sent anonymous samples covering a wide range of radiocarbon ages and carbon compositions. These included materials like wood, peat, shell, and bone, selected to represent common but analytically challenging substances. A key methodological feature was the inclusion of "known-age" samples, such as those from the Irish Oak chronology or historically dated artifacts, which provided a benchmark for assessing accuracy. Laboratories employed their standard pretreatment and measurement techniques, whether gas proportional counting, liquid scintillation counting, or the then-emerging accelerator mass spectrometry, with all results collated centrally for statistical analysis.

Participating Laboratories and Materials

The intercomparison engaged an unprecedented international community, with over 100 laboratories from more than 30 countries taking part. This included major facilities like the University of Arizona's NSF-Arizona AMS Laboratory, the University of California, Irvine, and the Chrono Centre at Queen's University Belfast. Renamed institutions such as the Scottish Universities Environmental Research Centre were also key participants. The sample suite was extensive, featuring materials like Whale bone from the Smithsonian Institution, cellulose from Douglas fir, and foraminifera from deep-sea cores, ensuring the test of laboratory proficiency across diverse carbon reservoirs and potential contaminants.

Key Results and Findings

The consolidated results revealed a generally high level of competence but exposed significant outliers and systematic biases in some laboratory procedures. Key findings showed that discrepancies often stemmed from variations in sample pretreatment chemistry, particularly for complex materials like bone collagen. The data also highlighted the superior precision of accelerator mass spectrometry for small samples. Statistical analysis, often referencing standards from the International Atomic Energy Agency, provided clear evidence for the need for robust error reporting and the importance of using consensus values for secondary standards. The final report, published in the journal Radiocarbon, became a foundational reference.

Impact on Radiocarbon Dating

The intercomparison had a profound and lasting impact on the field. It directly led to the formalization of international quality assurance protocols, which were later endorsed by bodies like the International Union for Quaternary Research. The exercise strengthened the credibility of radiocarbon dating for resolving major debates, such as the timing of the extinction of the mammoth or the spread of Austronesian peoples. It also encouraged more rigorous laboratory inter-comparison as a routine practice, improving the reliability of large-scale projects like the INTIMATE event stratigraphy and the European Pollen Database.

Subsequent Intercomparison Exercises

The success of the initial effort spawned a continuing tradition of international comparison. Follow-up exercises, such as those coordinated by the University of Oxford's Radiocarbon Accelerator Unit or the VIRI (Third International Radiocarbon Intercomparison) project, have built upon its framework. These subsequent rounds have incorporated newer challenges, including the dating of compound-specific materials and samples affected by nuclear testing (the bomb pulse). The ongoing work, often presented at conferences of the European Association of Archaeologists, ensures that the community maintains the high standards of accuracy and comparability established by the pioneering International Radiocarbon Intercomparison.

Category:Radiocarbon dating Category:Scientific techniques Category:Archaeological science