• 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.
    • 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.
    • Radiocarbon Dating of Intercomparison Samples at the Zagreb Radiocarbon Laboratory

      Horvatinčić, Nada; Srdoč, Dušan; Obelić, Bogomil; Krajcar Bronić, Ines (Department of Geosciences, The University of Arizona, 1990-01-01)
      The Radiocarbon and Tritium Laboratory of the Rudjer Bošković Institute, Zagreb, participated in the International Collaborative Study (ICS) in all three stages. All measurements were made by proportional counting of methane. We present here a statistical analysis of our results. A comparison with the mean or median values of reported ICS values showed that our results are generally slightly younger.
    • Report on Stage 3 of the International Collaborative Program

      Aitchison, T. C.; Scott, E. Marian; Harkness, D. D.; Baxter, M. S.; Cook, G. T. (Department of Geosciences, The University of Arizona, 1990-01-01)
      This report on the third and final stage of the International Collaborative Program concentrates on the analysis of internal and external variability of 14C dates obtained from samples involved in the full 14C dating process. Thirty-eight laboratories took part in this stage with most producing 8 14C dates from 3 sets of duplicate material (eg, wood, shell and peat) and 2 single samples of wood of known ages 190 yr BP apart. From the 3 sets of duplicates for each laboratory, the internal precision of most laboratories was adequate; 6 labs grossly underestimated their internal reproducibility. From the 14C determinations from the 5 distinct samples for each laboratory, we discovered significant systematic biases, often greater than 100 years, in 15 laboratories and even accounting for bias, 12 laboratories had significantly greater external variability than explained by their quoted errors. In total, 23 out of the 38 laboratories in this stage of the study, FAILED to meet these 3 basic criteria for an adequate performance in the production of 14C dates.
    • Sources of Random Error in the Debrecen Radiocarbon Laboratory

      Hertelendi, Ede (Department of Geosciences, The University of Arizona, 1990-01-01)
      A new high-pressure methane-filled counter system for 14C dating was installed in 1986 when the first stage of the International Collaborative Study (ICS) started. Random errors in the new measuring system and in the process of chemical pretreatment and preparation were checked during the three years of intercomparison. Results show that the most important source of error in our laboratory is gas contamination. This causes variation of the count rate to exceed the statistically expected variability. Other sources of error are also discussed and limits of their contributions are given.
    • Statistical Quality Control Graphs in Radiocarbon Dating

      Switsur, Roy (Department of Geosciences, The University of Arizona, 1990-01-01)
      I describe here the establishment and use of statistical control graphs based on the analysis of variance for monitoring the stability of operation of radiocarbon dating counting systems.