• International Collaborative Study: Structuring and Sample Preparation

      Cook, G. T.; Harkness, D. D.; Miller, B. F.; Scott, E. Marian; Baxter, M. S.; Aitchison, T. C. (Department of Geosciences, The University of Arizona, 1990-01-01)
      The success of any intercomparison exercise depends largely on participation and cooperation of a sufficient number of laboratories and the selection of a suitable suite of samples. Unless the latter is satisfactorily devised, the former cannot be guaranteed. The hierarchical nature of this study has necessarily resulted in a far more comprehensive set of sample types than has previously been employed. The exercise was structured to satisfy the following criteria: 1) to enable the participating laboratories to assess the experimental precision and accuracy of the component stages of the dating process; 2) samples should be typical of those routinely dated by the laboratories. This takes on a particular significance in Stage 1 where they should resemble as closely as possible the counting medium; 3) an objective statistical analysis of the results at each component stage of the study.
    • 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.
    • Radiocarbon Dating Reproducibility at the Museo de la Plata Radiocarbon Laboratory

      Figini, Anibal J.; Huarte, Roberto; Carbonari, Jorge (Department of Geosciences, The University of Arizona, 1990-01-01)
      We discuss here the variability, for our laboratory, in counting for radiocarbon dating of replicate measurements of background and secondary modern standard, duplicate measurements of samples provided by the International Collaborative Study, and replicate measurements of the dilution of the 14C-labeled benzene standard. The variability in the measurements of the International Collaborative Study samples suggest the existence of systematic bias.
    • 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.
    • Routine Checks in the Uppsala Conventional 14C Laboratory to Achieve Reliable Results

      Olsson, Ingrid U. (Department of Geosciences, The University of Arizona, 1990-01-01)
      I describe here a series of routine self-checks that the Uppsala 14C laboratory performs with all measurements. We estimate all uncertainties in the physical measurement of a sample. We study long-term stability, calculate mean values for oxalic acid and background and compare expected and real statistical distributions of uncertainties. To reduce the risk of bias, the samples from each series are almost exclusively run on the same counter. Some samples are, however, run on two or more counters to check the possible bias to achieve reliable activity comparisons with other laboratories. It is always possible to trace which counter is used, since different number series are used for different counters.
    • 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.
    • Time-Resolved Liquid Scintillation Counting

      Kessler, Michael (Department of Geosciences, The University of Arizona, 1990-01-01)
      Historically, scientists who perform low-level measurements of 14C for age dating, and 3H2O for environmental contamination, have purchased or constructed highly specialized instruments to quantitate low-level radionuclides using a general-purpose liquid-scintillation analyzer (LSA). The LSA uses special time-resolved 3-D spectrum analysis (TR-LSC) to reduce background without substantially affecting sample counting efficiency. This technique, in combination with a special slow fluor scintillating plastic, further reduces the minimal detectable limit for the TR-LSC liquid scintillation counter.