• 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.
    • 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.
    • 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.
    • 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.