• Participants

      Department of Geosciences, The University of Arizona, 1990-01-01
    • Price List

      Department of Geosciences, The University of Arizona, 1990-01-01
    • Professor of Geosciences Purdue University

      Department of Geosciences, The University of Arizona, 1990-01-01
    • Radiocarbon Announces the Forthcoming Publication of the Following Special Issues:

      Department of Geosciences, The University of Arizona, 1990-01-01
    • 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 Problems Using Acetylene as Counting Gas

      Geyh, Mebus A. (Department of Geosciences, The University of Arizona, 1990-01-01)
      An investigation of inconsistent Hannover results in the International Collaborative Study (ICS) led to the conclusion that the main reason was contamination of the acetylene used as counting gas with recent and/or fossil carbon by the lithium used for its preparation. Despite the high level of purity of the lithium guaranteed by the producer and storage under argon in cans, different charges were partly covered with contemporary lithium carbonate and fossil oil sometimes was used to preserve the metal. Thorough cleaning of the surface of the lithium rods decreased the contamination but did not remove it entirely, which is evidenced in the wider scatter of the counting rates of various background gases than that of radiocarbon-free tank acetylene. As a result of the high risk of contamination with fossil and/or recent carbon from the acetylene counting gas, the high price of lithium, and the time-consuming preparation, the Hannover 14C Laboratory will use carbon dioxide instead of acetylene as counting gas in the future.
    • 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 of the International Workshop of Intercomparison of Radiocarbon Laboratories: A Summary of the Meeting

      Baxter, M. S. (Department of Geosciences, The University of Arizona, 1990-01-01)
    • 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.
    • Second Announcement

      Department of Geosciences, The University of Arizona, 1990-01-01
    • 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.
    • Systematic Biases in Results of the International Collaborative Study and Their Probable Sources

      Pazdur, Mieczysław F.; Awsiuk, Romuald; Goslar, Tomasz; Pazdur, Anna (Department of Geosciences, The University of Arizona, 1990-01-01)
      Results of the International Collaborative Study show an unexpectedly large scatter of individual dates as well as systematic biases. Very high values of linear correlation coefficients are observed for all results of Stage 2 and for benzene samples of Stage 1. We observed moderate correlations for carbonate samples and the lowest for natural samples of wood and peat of Stage 3. The correlation is practically negligible among results obtained in different stages. The probable reasons for such effects are seen in medium-term changes in the calibration of the counting systems.
    • Tentative Conference Sessions

      Department of Geosciences, The University of Arizona, 1990-01-01
    • 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.