• Background Measurements with Different Shielding and Anticoincidence Systems

      Loosli, H. H.; Forster, Markus; Otlet, R. L. (American Journal of Science, 1986-01-01)
      Extremely low background count rates are a necessary condition for both the measurement of 39Ar concentrations in ground and ocean water and of 14C activities in small samples using gas proportional counting techniques. A systematic comparison of the performance of three different designs of shielding systems in four different installations has been made. Background values of selected gas proportional counters were measured, compared and separated into their various components. Acceptably low backgrounds were obtained in all the systems tried. The performance of a Nail shield in a surface laboratory was found to be at least equal to the best obtained with a gas ariticoincidence detector in a deep underground laboratory.
    • Bomb Produced 14C Content in Tree Rings Grown at Different Latitudes

      Dai, Kai-Mei; Fan, C. Y. (American Journal of Science, 1986-01-01)
      The 14C content in 1961-1967 rings of each of three spruce pines grown at (68 degrees N, 130 degrees W), (47 degrees 30' N, 129 degrees 16' E) and (27 degrees 13' N,100 degrees 20' E) were measured. Delta-14C values of the three specimens rise dramatically from a common level (~250 per mil) in 1961 to their respective maxima, 964 per mil, 909 per mil, and 743 per mil in 1964 and then fall to a common level ~680 per mil in 1967. The observed Delta-14C increase comes most likely from the nuclear bomb test of the USSR at 75 degrees N in 1961, although there were many other tests since the 1950s. The different effects at different latitudes reflect the atmospheric circulation patterns in the stratosphere and the transport of 14C nuclei from the stratosphere to the troposphere.
    • Carbon Cycle: 1985 Glacial to Interglacial Changes in the Operation of the Global Carbon Cycle

      Broecker, Wallace S.; Peng, Tsung-Hung (American Journal of Science, 1986-01-01)
      The hottest topic for those interested in the earth's carbon cycles is the change in atmospheric CO2 content between glacial and interglacial time. What caused it? What is its role in glacial cycles? We evaluate here the hypotheses that have been put forward to explain the CO2 change with evidence from deep sea sediments. We conclude that all the hypotheses have serious drawbacks and that much effort will have to be expended in gathering more data from ice cores and ocean sediments before we will be pointed toward the correct scenario. Also, thoughtful modeling aimed at depicting the ties between pCO2, O2, 13C/12C, 14C/12C, and nutrient constituents in the sea for various modes of circulation will have to be done before the evidence from ocean cores can be properly interpreted.
    • Carbon Isotopes in Atmospheric CO2 of the Krakow Region: A Two-Year Record

      Kuc, Tadeusz (American Journal of Science, 1986-01-01)
      We have been measuring concentration of atmospheric CO2 and its carbon isotope composition in the Kraków region for about two years. Samples are continuously collected at two-week intervals at ca 20m above ground level, close to the center of the industrialized urban area. Sampled atmospheric CO2 is sorbed in a molecular sieve and, after recovery by heating, is converted to benzene. 14C is measured in a liquid scintillation spectrometer, and delta-13C of the CO2 is determined in a mass spectrometer. The annual record shows winter-summer variation of 14C, 13C, and CO2 concentration. A long-term trend for 1983 and 1984 indicates a slight decrease of 14C activity (122.0 in January 1983; -1.2% per year), a permanent decrease of delta-13CPDB (-9.3 per mil in January 1983; -0.3 per mil per year) and an increase of CO2 concentration (344ppm in January 1983; 1.4ppm per year).
    • Dating of Holocene Stratigraphy with Soluble and Insoluble Organic Fractions at the Lubbock Lake Archaeological Site, Texas: An Ideal Case Study

      Haas, Herbert; Holliday, Vance; Stuckenrath, Robert (American Journal of Science, 1986-01-01)
      The Lubbock Lake site, on the Southern High Plains of Texas, contains one of the most complete and best-dated late Quaternary records in North America. A total of 117 14C dates are available from the site, determined by the Smithsonian and SMU Laboratories. Of these dates, 84 have been derived from residues (humin) and humates (humic acids) of organic-rich marsh sediments and A horizons of buried soils. Most of the ages are consistent with dates determined on charcoal and wood, and with the archaeologic and stratigraphic record. The dates on the marsh sediments are approximate points in time. Dates from the top of buried A-horizons are a maximum for burial and in many cases are close to the actual age of burial. Dates from the base of the A-horizons are a minimum for the beginning of soil formation, in some cases as much as several thousand years younger than the initiation of pedogenesis. A few pairs of dates were obtained from hurnin and humic acid derived from split samples; there are no consistencies in similarities or differences in these age pairs. It also became apparent that dates determined on samples from scraped trench walls or excavations that were left open for several years are younger than dates from samples taken from exactly the same locations when the sampling surfaces were freshly excavated.
    • Dating Polar Ice by 14C Accelerator Mass Spectormetry

      Andree, Michael; Beer, Jürg; Loetscher, H. P.; Moor, Ernst; Oeschger, Hans; Bonani, Georges; Hofmann, Hans Jakob; Morenzoni, Elvezio; Nessi, Marzio; Suter, Martin; et al. (American Journal of Science, 1986-01-01)
      Results of 14C/12C ratio measurements on CO2 extracted from air bubbles in polar ice are presented. The samples investigated originate from the Dye 3, South Greenland, deep ice core and span approximately the last 10,000 years. The results are calibrated with tree-ring records. The 14C ages are compared with information obtained from seasonal variations of ice-core parameters and rheologic model calculation.
    • delta-13C and Diet: Analysis of Norwegian Human Skeletons

      Johansen, Olav Sverre; Gulliksen, Steinar; Nydal, Reidar (American Journal of Science, 1986-01-01)
      The relationship between 13C content of human bone and the marine fraction in the individual diet is well established. In the present investigation human skeletons from inland and coastal areas in Norway were analyzed. Both regional and chronologic differences are revealed, and larger variability than expected at specific sites indicate more complex cultural adaptations than earlier recognized. Extremely high delta-13C values, comparable with those obtained from Eskimo sites, are found for material from Early Stone Age fishing/hunting communities.
    • Dendrochronology—The Absolute Irish Standard

      Brown, D. M.; Munro, M. R.; Baillie, M. G. L.; Pilcher, J. R. (American Journal of Science, 1986-01-01)
      Since the 11th International Radiocarbon Conference considerable advances have been made in European dendrochronology giving several long continuous absolute chronologies. Recent collaboration between European laboratories provides confirmation of the accuracy of these chronologies and, thus, of the standards used for radiocarbon calibration.
    • Detection of Bias in the Background of Vials Used for Scintillation Counting

      Ambers, Janet; Leese, Morven; Bowman, Sheridan (American Journal of Science, 1986-01-01)
      Inter-vial variation in background of the glass vials used in liquid scintillation counting can introduce appreciable errors into 14C measurements. Our aim was to measure the background in each of 50 glass vials, under the same conditions as far as possible, in order to find a self-consistent set for use in 14C dating. The criteria, statistical tests, and possible errors introduced by not making such checks are discussed.
    • Discordant Ages Related to Reservoir Effect of Associated Archaeologic Remains from the Tunel Site, Beagle Channel, Argentine Republic

      Albero, Miguel C.; Angiolini, Fernando E.; Piana, Ernesto L. (American Journal of Science, 1986-01-01)
      Evidence of a tradition of human maritime adaptation was recovered from various sites at Beagle Channel dating back to ca 6000 yr BP. Final occupations date to European settlement in the 19th century. The Túnel site exhibits discontinuous human occupation ranging from 6000 to 500 yr BP, represented by different archaeologic remains in each layer. Associated charcoal, mollusk shells, and Lama guanicoe and Arctocephalus australis bones were dated. Shells and Arctocephalus are consistently older than charcoal, demonstrating the reservoir effect at Beagle Channel. Results encourage further work in the area to evaluate the spatial and temporal magnitude of the effect.
    • Early Slavonic Settlements and Navigation at the Mouth of the Odra River

      Awsiuk, Romuald; Filipowiak, Władyslaw; Goslar, Tomasz; Pazdur, Anna; Pazdur, Mieczysław F. (American Journal of Science, 1986-01-01)
      An attempt is presented to establish an absolute chronology of early Slavonic habitation in the region of the mouth of the Odra River up to the Baltic and to find associations with a series of stave boats and dugouts of different levels of technology and navigation. The methodology of the research project is presented and some conclusions of a general nature are drawn from the results already obtained.
    • Environmental 14C Levels Around the 632 MWe Nuclear Power Plant Krško in Yugoslavia

      Obelić, Bogomil; Krajcar-Bronić, Ines; Srdoč, Dušan; Horvatinčić, Nada (American Journal of Science, 1986-01-01)
      Measurements of 14C activity of atmospheric CO2, vegetables, and tree rings in the area of the 632 MWe power plant Krško in Slovenia, NW Yugoslavia, have been in progress since January, 1984. Sampling stations are located in the area ca 400km2 and are distributed in the direction of the prevailing westerly winds. The closest sampling point is 1.5km NE of the plant exhaust stack, the farthest sampling point is 30km E of the plant. A sampling site at National Park Plitvice in central Croatia was chosen as the 14C reference point not affected by the power plant. An average excess of 2.2% above the reference point activity during normal periods of reactor operation was observed 1.5km from the plant smokestack. Calculations of the 14C release from the power plant was estimated at 0.1 TBq/a. The tree ring activity near the plant followed the 14C activity of the Northern Hemisphere in the past decade. No influence of the power plant release was observed on the tree ring activity.
    • Establishment of a Working Data Base for the International Exchange of 14C Data Using Universal Transfer Formats

      Wilcock, J. D.; Otlet, R. L.; Walker, A. J.; Charlesworth, S. A.; Drodge, J. (American Journal of Science, 1986-01-01)
      A high-level record structure for the international communication of 14C data bases is proposed. The record structure is based on the high-level communication format first proposed by the authors at the 23rd International Symposium on Archaeometry, Naples, 1983 and does not require the abandonment of existing systems. A description is given of an implementation of the high-level system at Harwell, with examples of retrieval in an international format (the Radiocarbon date list format) and a keyword-organized local format.
    • Fast and Complete CO2-to-Graphite Conversion for 14C Accelerator Mass Spectrometry

      Hut, Gert; Östlund, H. Göte; van der Borg, Klaas (American Journal of Science, 1986-01-01)
      With Fe powder as a catalyst, CO2 is completely converted to graphite within 90 minutes. The reaction proceeds at 650 degrees C with an excess of H2. The reaction rate is enlarged by forced circulation and by keeping the water vapor pressure very low. The graphite samples obtained, consisting of 5mg of carbon, almost immediately produce stable 12C- currents of the order of 20-30 micro-A in the sputter source of a Van de Graaff accelerator. The currents can be maintained for at least 10 hours and are comparable to those from commercial graphite. No memory effects in the preparation system have been observed.
    • Foreword

      Stuiver, Minze (American Journal of Science, 1986-01-01)
    • Geomagnetic-Heliomagnetic Modulation of Atmospheric Radiocarbon Production

      Damon, Paul E.; Linick, Timothy W. (American Journal of Science, 1986-01-01)
      New Arizona high precision Delta-14C data back to 6500 BC plot close to an 11,300-yr period sinusoid extrapolated from the post 5300 BC data (offset = +32 per mil, half amplitude = 51 per mil and phase lag = 2.29 radians). The trend curve is modulated by high latitude components of the non-dipole field with a fundamental period of 2400 yr. Based upon a model of Lund and Banerjee (1985), the non-dipole field rotates and every 1200 yr the high latitude maxima pass over the north magnetic pole and near the south magnetic pole in reversed polarity. This modulates cosmic ray production producing extended maxima ca AD 1700, 700 BC, 3100 BC, and 5500 BC. The 2400 period appears to be stationary. The magnetic field also modulates the amplitude of the solar activity induced cycles of periods 200, 80, and 11 yr as can be seen in the Zürich-Bern Camp Century ice core data as well as in the Delta-14C fluctuation data. Reinterpretation of the Camp Century 10Be data indicates that it is in agreement with magnetic field as well as solar activity modulation of terrestrial radioisotope production.
    • Global and Local Effects of 14C Discharges from the Nuclear Fuel Cycle

      McCartney, Martin; Baxter, M. S.; McKay, Keith; Scott, E. Marian (American Journal of Science, 1986-01-01)
      The radiologic impact of 14C produced by the nuclear fuel cycle is assessed at both global and local levels. In the former context, it is predicted here that the specific activity of atmospheric CO2 in the year 2050 will be ca 7.6 pCig^(-1)C. Although this is similar to the present level, the subsequent collective dose commitment could be highly significant. The enhancement of 14C concentrations around the nuclear fuel-reprocessing plant at Sellafield (Windscale) in Cumbria, UK has been monitored over recent years. For example, maximum levels of 27.2 pCig^(-1)C (~350% above natural) during 1984 were observed <1 km from the plant, with enhanced activities detectable to at least 29km. Nevertheless, it is clear that the radiologic significance to the local population is low. The spatial distribution of the excess 14C allows atmospheric dispersion models to be tested in the context of continuous releases and the results thus far show that the Gaussian plume model performs successfully.
    • Groningen 14C Data Base

      Endelsman, F. M. R.; Taayke, E.; Mook, W. G. (American Journal of Science, 1986-01-01)
    • Ice-Core Dating of the Pleistocene/Holocene Boundary Applied to a Calibration of the 14C Time Scale

      Hammer, Claus U.; Clausen, Henrik B.; Tauber, Henrik (American Journal of Science, 1986-01-01)
      Seasonal variations in 18O content, in acidity, and in dust content have been used to count annual layers in the Dye 3 deep ice core back to the Late Glacial. In this way the Pleistocene/Holocene boundary has been absolutely dated to 8770 BC with an estimated error limit of +/- 150 years. If compared to the conventional 14C age of the same boundary a value of Delta-14C = 53 +/- 13 per mil is obtained. This Delta-14C value suggests that 14C levels during the Late Glacial were not substantially higher than during the Postglacial.