Now showing items 21-26 of 26

    • Book Review: Isotopic Techniques in Water Resources Development 1991, G. V. Ramesh (Ed.)

      Long, A. (Department of Geosciences, The University of Arizona, 1993-01-01)
    • An Assessment of the Radiocarbon Dating of the Dead Sea Scrolls

      Rodley, G. A. (Department of Geosciences, The University of Arizona, 1993-01-01)
      I suggest, on the basis of a statistical analysis, that recently determined 14Conventional radiocarbon ages" of Dead Sea Scroll documents are offset systematically by about +40 yr, leading to a similar overestimate of the ages of these documents. Much closer agreement with paleographic and specific dates is obtained when a correction of this magnitude is made to the 14Conventional 14C" values. This indicates that 14C dates may convey more precise information about the ages of these documents than initially recognized.
    • AMS-Graphite Target Production Methods at the Woods Hole Oceanographic Institution During 1986-1991

      Gagnon, Alan R.; Jones, Glenn A. (Department of Geosciences, The University of Arizona, 1993-01-01)
      In July 1986, an AMS radiocarbon target preparation laboratory was established at the Woods Hole Oceanographic Institution to produce graphite to be analyzed at the NSF-Accelerator Facility for Radioisotope Analysis at the University of Arizona (Tucson). By June 1991, 923 graphite targets had been prepared and 847 analyzed. Our lab procedures during this time included the careful documentation of weights of all starting samples, catalysts and final graphite yields, as well as the volume of CO2 gas evolved during CaCO3 hydrolysis or closed-tube organic carbon combustions. From these data, we evaluate the methods used in general and in our lab.
    • A Simplified Approach to Calibrating 14C Dates

      Talma, A. S.; Vogel, J. C. (Department of Geosciences, The University of Arizona, 1993-01-01)
      We propose a simplified approach to the calibration of radiocarbon dates. We use splines through the tree-ring data as calibration curves, thereby eliminating a large part of the statistical scatter of the actual data points. To express the age range, we transform the +/- 1 sigma and +/- 2 sigma values of the BP age to calendar dates and interpret them as the 68% and 95% confidence intervals. This approach bypasses the conceptual problems of the transfer of individual probability values from the radiocarbon to the calendar age. We have adapted software to make this calibration possible.
    • A Batch Preparation Method for Graphite Targets with Low Background for AMS 14C Measurements

      Kitagawa, Hiroyuki; Masazawa, Toshiyuki; Nakamura, Toshio; Matsumoto, Eiji (Department of Geosciences, The University of Arizona, 1993-01-01)
      We have developed a method of graphitization from CO2 samples for accurate 14C measurements by accelerator mass spectrometry. Our batch method, using a sealed Vycor tube, reduces the risk of contamination during graphitization and makes it possible to prepare many samples in a short time (typically 20 samples per day).
    • 14C Dating of Laser-Oxidized Organics

      Watchman, A. L.; Lessard, R. A.; Jull, A. J. T.; Toolin, L. J.; Blake, Weston (Department of Geosciences, The University of Arizona, 1993-01-01)
      We used a continuous krypton ion laser to rapidly oxidize milligram-sized fragments of coniferous driftwood of known ages, and dated the resulting carbon dioxide by accelerator mass spectrometry (AMS). AMS 14C ages of non-pretreated young wood from different parts of two logs were within 10% of the ages of conventionally determined alkaline insoluble fractions. The age of the oldest whole wood measured after laser oxidation was within the error ranges of conventional values.