• Intercalibration of Environmental Isotope Measurements: The Program of the International Atomic Energy Agency

      Gonfiantini, Roberto; Rozanski, Kazimierz; Stichler, Willibald (Department of Geosciences, The University of Arizona, 1990-01-01)
      We briefly present here the environmental isotope intercalibration programs of the International Atomic Energy Agency (IAEA). In fact, the IAEA has implemented two parallel programs during the last 20 years: for stable isotopes of light elements and for a radioactive isotope of hydrogen, tritium. This IAEA activity resulted in the preparation of a number of reference and intercomparison materials of various types, now stored in the Agency and available upon request.
    • High-Precision Intercomparison at IsoTrace

      Beukens, Roelf P. (Department of Geosciences, The University of Arizona, 1990-01-01)
      I conducted a high-precision comparison at the 0.2% to 0.3% level with samples supplied by the radiocarbon laboratory of the Quaternary Research Center at the University of Washington (QRC). Four samples with ages ranging from modern to > 50,000 BP were dated in a blind test. The absence of cosmic-radiation background in AMS dating is a major advantage for dating samples > 35,000 BP. The reliability of AMS dates > 35,000 BP depends entirely on understanding the contamination processes. By comparing results with laboratories capable of sample enrichment, such as QRC, it is possible to identify and estimate the intrinsic 14C in the background samples as well as the contamination introduced by sample preparation.
    • Checking Back on an Assemblage of Published Radiocarbon Dates

      Baillie, M. G. L. (Department of Geosciences, The University of Arizona, 1990-01-01)
      It is clear that radiocarbon researchers take a forward view towards the improvement of accuracy and precision in dating. Unfortunately, archaeologists base much of their research on the published dates produced in the past. Archaeologists and other users of radiocarbon dates should understand the limitations associated with past dates. This article addresses these limitations by looking at a large number of routine radiocarbon dates associated with a block of English tree-ring chronologies, the true ages of which are now known within close limits. My conclusion supports the idea of global multiplication factors as proposed by the International Study Group (1982).
    • An Overview of Some Interlaboratory Studies

      Scott, E. Marian; Baxter, M. S.; Aitchison, T. C.; Harkness, D. D.; Cook, G. T. (Department of Geosciences, The University of Arizona, 1990-01-01)
      Many interlaboratory studies have been made in the 14C community at irregular intervals over the past ten years. At times, the results from these studies have been contentious, mostly because of the lack of consistency in their findings. The importance of regular exercises has become particularly acute due to the large number of operating laboratories and the diversity of their methodologies. Hence, we briefly review the studies that have been made in the 1980s, focusing on those in which our laboratories participated. These include the 14C Interlaboratory Comparison in the UK (Otlet et al 1980), the International Comparison (ISG 1982, 1983) and the first two parts of the current International Collaborative Program (Scott et al 1989a, b). The development of each study, its findings and shortcomings, are highlighted in order to assess the concordance of the conclusions.
    • An Overview of All Three Stages of the International Radiocarbon Intercomparison

      Scott, E. Marian; Aitchison, T. C.; Harkness, D. D.; Cook, G. T.; Baxter, M. S. (Department of Geosciences, The University of Arizona, 1990-01-01)
      The International Collaborative Study involved a wide range of sample materials and ages and, on completion, assessed each stage independently (Scott et al 1989; Aitchison et al 1990). We combine here the three stages of the study and provide an overview of the uncertainties in the dating procedure as a whole and in its component processes. Three key optimal performance indices, related to internal and external precision and to bias, have been defined to allow quantitative assessment of Internal Consistency and External Consistency (Aitchison et al 1990). We believe that these measures provide quantitative descriptions of a laboratory's reproducibility, accuracy and precision. For the internal consistency, we have defined the Internal Error Multiplier of the quoted error and, for the external consistency of any laboratory relative to an appropriate baseline, we have defined two indices, the Systematic Bias and External Error Multiplier of the quoted error. We have evaluated the three indices over the three stages and have assessed the relative performances of gas counting, accelerator and liquid scintillation laboratories. The quoted errors describe adequately the variability in duplicate results, but there is evidence of systematic biases and underestimation of interlaboratory variability. We have considered the contribution of pretreatment, synthesis counting to the overall variability for each laboratory type. We found that, for liquid scintillation (LS) and gas counting (GC) laboratories, ca 66% of the total variation is due to counting and sample synthesis whereas, for accelerator mass spectrometry (AMS) laboratories, the major sources of variability are the sampling and pretreatment processes.
    • A Suggested Quality Assurance Protocol for Radiocarbon Dating Laboratories

      Long, Austin; Kalin, Robert M. (Department of Geosciences, The University of Arizona, 1990-01-01)
      The current intercomparison of data from 14C laboratories reveals significant variability among liquid scintillation laboratories, suggesting that identical samples submitted to different laboratories may yield values that differ by much more than expected on a purely statistical basis. Erroneous dates (recently corrected) by a well-established 14C laboratory give rise to further concern for quality 14C data. Thus, it is incumbent on each laboratory to develop and implement a quality assurance and control (QA/QC) program in order to ensure accuracy of results and to alert lab personnel to problems. Samples of pure materials (eg, benzene, cellulose) distributed by national or international standardizing groups are valuable, but are not representative of typical samples routinely run in most labs. Inevitably, 14C personnel take special care with intercomparison samples and data that "outsiders" will be scrutinizing and comparing. Here, we reiterate Stuiver and Pearson's (1986) concept of laboratory error multiplier (K-value) and make the case for internally-generated QA/QC programs. We recommend that an ongoing, internal, self-test QA/QC protocol, to be designed and approved at the next 14C conference, is the most practical and effective method of assuring quality of 14C laboratory data. Each laboratory would then be responsible for determining its error multiplier factor by performing analyses on one or more homogeneous batches of wood chips, cellulose or calcite. Laboratories would update these data as they see fit and make this information available in a standard format to all who use their data.
    • A Quality Assurance Protocol for Radiocarbon Laboratories

      Long, Austin (Department of Geosciences, The University of Arizona, 1990-01-01)
    • A Consideration of Some Basic Ideas for Quality Assurance in Radiocarbon Dating

      Switsur, Roy (Department of Geosciences, The University of Arizona, 1990-01-01)
      Most radiocarbon ages are readily accepted by researchers in all disciplines. It is recognized, however, that discrepancies appear in the literature. These problems have been highlighted by the International Collaborative Study. The introduction of quality control and assurance techniques used in some laboratories for many years could reduce or eliminate aberrant results. I present here some of the basic considerations of this approach in the processes of conventional radiocarbon dating.