• 14C Background Levels in an Accelerator Mass Spectrometry System

      Vogel, J. S.; Nelson, D. E.; Southon, J. R. (American Journal of Science, 1987-01-01)
      The levels and sources of the measurement background in an AMS 14C dating system have been studied in detail. The relative contributions to the total background from combustion, graphitization, storage, handling, and from the accelerator were determined by measuring the 14C concentrations in samples of anthracite coal ranging in size from 15 micrograms to 20mg. The results show that, for the present system, the uncertainty in the background is greater than that due to measurement precision alone for very old or for very small samples. While samples containing 100 micrograms of carbon can yield useful 14C dates throughout the Holocene, 200 to 500 micrograms are required for dating late Pleistocene materials. With the identification of the procedures that introduce contamination, the level and uncertainty of the total system background should both be reducible to the point that 100 micrograms of carbon would be sufficient for dating most materials.
    • 14C Traced in Kraków After the Chernobyl Accident

      Kuc, Tadeusz (American Journal of Science, 1987-01-01)
      Results of the 14C measurements in atmospheric CO2 in the first half of 1986 are presented. CO2 samples were systematically collected in Krakow in two-week cycles and, after conversion to benzene, measured in a liquid scintillation spectrometer. 14C activity and 13C/12C ratio are reported as delta-14C and delta-13CPDg, respectively. For about three weeks after April 26, 1986 (the Chernobyl accident) an increase of ~9% above the normal level for Krakow was observed. A rough estimate of the 14C release to the lower atmosphere during the accident gave a value 900 Ci, which is ~1.8 x 10^5 of the total activity released to the atmosphere.
    • An Assessment of Laboratory Contamination at the IsoTrace Radiocarbon Facility

      Gurfinkel, D. M. (American Journal of Science, 1987-01-01)
      An assessment of the contamination contribution of various sample preparation procedures used at the Isotrace Radiocarbon Facility, University of Toronto, is described. Samples of geologic material, millions of years old, or samples derived therefrom, were tested because these would presumably contain only dead carbon. Results showed, however, that 14C contamination could be detected in several samples, complicating the contamination assessment. Best estimates of the contamination contribution from sample preparation were reported as: cracking: <0.17% modern, acetylene synthesis: <0.25% modern, combustion: <0.39% modern, and handling: <0.54% modern. These estimates were reported as upper limits because they likely represented 14C derived from two sources: sample preparation and the sample itself.
    • Climatic Implications of Chenier Dates in Northern Australia

      Lees, Brian G.; Clements, Annemarie (American Journal of Science, 1987-01-01)
      The characterization of late Holocene climates in northern Australia has, in the past, been based on local investigations. This examination of the chenier record of northern Australia indicates that there has been a statistically significant regional change in conditions between 1600-2800 years BP, possibly a period of relative aridity. Support for this conclusion may be found in the vegetation record from the Atherton Tableland where numerical comparisons of dryland fossil and modern pollen spectra suggest that rainfall may have been up to 50% higher during the period 7000 to 3000 BP.
    • Index Volume 29, Nos. 1 to 3, 1987: Geological Samples

      American Journal of Science, 1987-01-01
    • Laboratories

      American Journal of Science, 1987-01-01
    • Measurement of Small Volume Oceanic 14C Samples by Accelerator Mass Spectrometry

      Schlosser, P.; Pfleiderer, C.; Kromer, Bernd; Levin, Ingeborg; Münnich, K. O.; Bonani, Georges; Suter, Martin; Wölfli, Willy (American Journal of Science, 1987-01-01)
      A technique for 14C measurement of small volume (0.5L) oceanic water samples by Accelerator Mass Spectrometry (AMS) is described. Samples were taken from a CTD/rosette system used for standard hydrographic work. After CO2 extraction and target preparation, the samples were measured at the Zürich tandem accelerator facility. On the basis of 14C data from samples collected on a station in the northern Weddell Sea, the precision of the measurements is estimated to ca +/- 8 per mil. The error in the present AMS results is dominated by the statistical error in 14C detection. From results of duplicate targets, it is concluded that a precision of +/- 5 per mil can be reached. The 14C data are discussed in relation to the Weddell Sea hydrography.
    • Radiocarbon Dates from Two Coastal Sites in the Manu'a Group, American Samoa

      Hunt, T. L.; Kirch, P. V. (American Journal of Science, 1987-01-01)
    • Radiocarbon, Volume 29, Number 3 (1987)

      American Journal of Science, 1987-01-01
    • University of Granada Radiocarbon Dates IV

      Gonzalez-Gomez, Cecilio; Sanchez-Sanchez, Purificacion; Villafranca-Sanchez, Elena (American Journal of Science, 1987-01-01)
    • University of Lund Radiocarbon Dates XX

      Håkansson, Sören (American Journal of Science, 1987-01-01)
    • University of Wisconsin Radiocarbon Dates XXIV

      Steventon, Raymond L.; Kutzbach, John E. (American Journal of Science, 1987-01-01)
    • Vienna Radium Institute Radiocarbon Dates XVI

      Felber, Heinz (American Journal of Science, 1987-01-01)