• 13CO2 and 14CO2 Measurements on Soil Atmosphere Sampled in the Western Great Plains of the US

      Haas, Herbert; Fisher, D. W.; Thorstenson, D. C.; Weeks, E. P. (American Journal of Science, 1983-01-01)
      Soil gas samples were obtained from the unsaturated zone at eight sites in the Great Plains. Three of these sites were sampled extensively for gas composition and carbon isotopes. Sampling equipment consisted of a nest of gas probes vertically spaced by roughly 3m at most sites, generally approaching the water table. Water wells, 10cm in diameter, were screened in the topmost layer groundwater. Inverted cattle tanks were used to collect CO2 samples from the soil surface. The major gas components were analyzed with emphasis on CO2, Delta--13C, and 14C measurements. The same components were studied in groundwater samples. Higher than atmospheric CO2 concentrations were found in all soil samples. Root respiration and oxidation of organic matter were sources for the additional CO2. When lignite was present in the unsaturated zone, gaseous oxygen reacted almost completely, and CO2 levels rose to 19%. Near the surface, annual cycles in total CO2, Delta--13C, and 14C were observed. 14C activities were close to present post-bomb levels at the surface and generally declined with depth. At some sites, oxidation of lignite caused decline of 14C levels to 1 or 2% of their surface value at 8m depth. Without lignite, the 14C activity remained above 50% at all depths. Concentrations of total carbon and its isotopes in ground water remained very stable throughout the study. This implies that geochemical processes in the aquifer vary on time scales longer than the seasonal effects observed in the near-surface unsaturated zone.
    • 14C Dating and Magnetostratigraphy

      Thompson, Roy (American Journal of Science, 1983-01-01)
      The history of the earth's magnetic field is preserved in the fossil magnetism of archaeologic specimens, natural rocks and sediments. Samples such as lava flows and baked sherds that acquired a thermoremanent magnetization on cooling can be used to estimate ancient geomagnetic field intensities and directions. Paleofield directions can also be obtained from fine-grained sediments that acquired detrital magnetic remanence when deposited. Study of the earth's magnetic field over the last few tens of thousands of years yields information on geomagnetic dynamo theories, causes of fluctuations in cosmic-ray activity, and the formulation of a new regional chronologic tool.
    • 14C Variations During the Upper Pleistocene

      Vogel, J. C. (American Journal of Science, 1983-01-01)
      Parallel determinations of 14C and ionium dates on a stalagmite from the Cango Caves provide evidence of variations in the 14C content of the atmosphere beyond the range of the California tree-ring sequence. During the Holocene growth period the 230Th dates are compatible with the tree-ring calibrated 14C dates. At 18,000 BP and between 30,000 and 40,000 BP the 14C ages are markedly younger than the 230Th ages, suggesting that the 14C level of the atmosphere was considerably higher at these times. Between the 230Th ages of 35,000 and 29,000 BP the 14C ages remain nearly constant at 29,500 BP, indicating that 14C production must have been drastically reduced during this period. The 14C fluctuation is greater than that predicted by Barbetti (1980) but it may be explained by postulating a substantial increase in the geomagnetic dipole field, for which there is mounting evidence.
    • A Contribution to the Interpretation of 14C Groundwater Ages Considering the Example of a Partially Confirmed Sandstone Aquifer

      Eichinger, Lorenz (American Journal of Science, 1983-01-01)
      Previously described models and a new model were compared to determine the initial 14C content of groundwater in a partially-confined and unconfined sandstone aquifer (Fränkisches Albvorland, Germany). Isotope and chemical data were derived from samples of water, soil-CO2, and solid carbonates. The various 14C models lead to important differences in resulting groundwater ages. From the relationship between 14C and 2H or 18O concentrations of groundwater, it must be assumed that chemical and/or physical carbon isotope exchange between the DIC and the solid carbonate has occurred provided the groundwater with lower 18O and 2H concentrations was generated during the Pleistocene. Groundwater ages deduced from 14C and 39Ar concentrations showed discrepancies which can be explained if carbon isotope exchange between DIC and solid carbonate as well as mixing of recent and fossil waters is considered.
    • A Multiple Proportional 14C Counter System for Milligram-Sized Samples

      Hut, Gert; Keyser, Jan; Wijma, Stef (American Journal of Science, 1983-01-01)
      A system of 10 proportional 14C counters has been designed. The counters have a volume of 35ml and are operated with CO2 at a pressure of 1 bar and a voltage of 3300V. The amplified signals of the counters are fed through an analog multiplexer to the inputs of three discriminators. The Geiger signal is fed to a separate discriminator. A logic circuit selects from these discriminators the alpha, beta, muon, and purity counts which are then stored in a microcomputer (ITT 2020 with 48K RAM), where the necessary calculations are also performed. The purity of the gas sample is monitored by counting a part of the muon spectrum. The alpha and beta pulses are stored during 95% of the measuring period; the remaining 5% is used for registration of the muon and purity pulses. The overall accuracy of the system for modern carbon samples is 2% after a counting period of 6 days.
    • A Secondary Standard for Radiocarbon Dating

      Angiolini, Fernando E.; Albero, Miguel C. (American Journal of Science, 1983-01-01)
      The preparation and calibration of a secondary standard for the INGEIS Radiocarbon Dating Laboratory are presented. This standard is barium carbonate with a specific activity almost twice that of NBS oxalic acid. It was prepared from BaCO3 with high specific activity and commercial potassium carbonate by an isotopic dilution technique. The advantages of this standard are: 1) the preparation is simple and can be achieved with ordinary labware; 2) the production of CO2 by acid attack from this carbonate shows minimum isotopic fractionation. At least, it has less fractionation than wet oxidation of oxalic acid, the problems of which are described in the literature. This standard ensures better reproducibility in activity measurements; 3) despite some problems of activity exchange with atmospheric CO2 concerning carbonates, measurements of activity over a period of about two years have shown no significant deviation from the mean value. A tentative explanation of this phenomenon is also given. The activity ratio between BaCO3 and NBS oxalic acid is given with its error, and the statistical tests used in the calibration are briefly explained. Finally, a control chart for the activity of the standard over a long period is drawn, showing non-significant deviation and supporting the usefulness of this standard.
    • A System for Studying Carbon Allocation in Plants Using 11C-Labeled Carbon Dioxide

      Fares, Youhanna; Goeschl, J. D.; Magnuson, C. E.; Nelson, C. E.; Strain, B. R.; Jaeger, C. H.; Bilpuch, E. G. (American Journal of Science, 1983-01-01)
    • Accelerator Mass Spectrometry: From Nuclear Physics to Dating

      Kutschera, Walter (American Journal of Science, 1983-01-01)
    • An Evaluation of Shielding Characteristics Applicable to Mini-Gas-Proportional Counter-Based 14C Dating Systems

      Kaihola, Lauri; Kojola, Hannu; Polach, Henry; Soini, Erkki; Otlet, Robert (American Journal of Science, 1983-01-01)
      A mini-gas-proportional counter prototype of 10ml capacity (at NTP) was constructed of oxygen-free Finnish copper. The counter tube will be one of 16 equivalent tubes of a small-sample gas counting system, which is equipped with passive graded shield made of lead, cadmium, and copper and a dual active anticoincidence shield, consisting of an external cosmic gas-proportional and an internal plastic scintillation guard. The aim of this study was to evaluate the parameters leading to the design of a cost-effective and compact shielding package for mini-counters.
    • An International Reference Material for Radiocarbon Dating

      Mann, W. B. (American Journal of Science, 1983-01-01)
      In August 1980, the National Bureau of Standards (NBS) issued, in the form of oxalic acid, a new International Reference Material of contemporary 14C for use in radiocarbon dating laboratories. This reference material was to replace the 1975 oxalic-acid standard, supplies of which had been practically exhausted in 1978. The preparation of the new oxalic-acid standard was described in a preliminary report, as were, also, the results then available for the activity-concentration ratio of the new to the old standard obtained by a number of leading international laboratories. With the recent completion of the analysis of all results submitted by the participating laboratories, NBS plans to issue these recently calibrated samples of oxalic acid as an NBS Standard Reference Material. There is, however, no significant difference in the reported value of its activity concentration, relative to that of the 1957 standard, from that given provisionally in 1980. Subsequent to our report (Cavallo and Mann, 1980) a further measurement of relative activity concentration was reported by the Radiocarbon Laboratory of Peking University. Their value, and that also for Delta-13C, is insignificantly different from the average value of the results submitted by the eleven laboratories that participated in the international comparison organized by NBS.
    • Anthropogenic 14C Variations

      Segl, Monika; Levin, Ingeborg; Schoch-Fischer, Hilla; Münnich, Marianne; Kromer, Bernd; Tschiersch, Joche; Münnich, K. O. (American Journal of Science, 1983-01-01)
      Continuous 14C data of 1 or 2 weekly samples of atmospheric CO2 are presented, collected near two nuclear power plants (NPP-Biblis and NPP-Philippsburg) located in the rather densely populated upper Rhine valley. Tree-leaf and tree-ring samples from the area of a boiling water reactor in northern Germany (NPP-Würgassen) are also presented and discussed. Additional atmospheric 14CO2 samples from two continental ‘clean-air’ stations in Germany and Austria were used as reference for the polluted areas. For January 1982, these samples yield a ‘clean-air’ 14C concentration in central Europe of Delta-14C=255 +/- 5 per mil (7.7pCi/gC = 1.45pCi/m3 air). In the vicinity of boiling water reacctors we found a mean excess in Delta-14C activity of ca 53 per mil (0.05pCi/m3 air) above the local level during normal periods of reactor operation. During revision, however, the Delta-14C excess may reach up to 300 per mil above the local background. From this, we calculate source strengths of ca 20Ci/GWa on the average, with peak values of up to 2Ci/week during specific periods. Pressurized water reactors emit 14C mainly as hydrocarbons, and consequently, we found no additional 14CO2 near the Biblis reactor. Stations located in the Rhine valley show significant summer-winter 14CO2 variation due to intensive fossil-fuel combustion. The fossil-fuel admixture leads to a depression of the 14C level and reaches Delta-14Cdepr = 120 per mil in winter; summer values, however, are only slightly lower than the 'clean-air' level.
    • Anthropogenic Changes in Organic Carbon and Trace Metal Input to Lake Washington

      Schell, W. R.; Swanson, J. R.; Currie, L. A. (American Journal of Science, 1983-01-01)
      An example of how man's contaminants are introduced, deposited, and retained in sediments giving a chronological record of events has been developed for Lake Washington, Seattle. Significant amounts of both inorganic and organic compounds in the environment originate from fossil fuel sources, such as power plants and motor vehicles. Many organic compounds are introduced also from contemporary biogenic materials. Through the combined carbon isotope analysis technique (CCIA), we can distinguish between fossil and contemporary carbon sources classes (using 14C), as well as sources within each class (using 13C). To establish the chronology of the organic carbon pollutant input to the lake sediment, the ages of the layers were determined using 210pb dating techniques. Sediment profiles of trace metals and a fallout radionuclide plutonium were also obtained and compared with the carbon isotope profiles. The results show that the total organic carbon (TOC) concentration correspond to 93% modern carbon before 1905. This 14C concentration in TOC decreased to ∼60% modern in the 1930's and now is between 95 and 80% modern. The lipid fraction is ca 30% modern and the total aromatic hydrocarbon fraction reached a minimum of 5% modern in 1954. The large decrease in 14C of TOC around 1930 is believed to be due to coal dust or fly ash. The trace metal concentration also increased substantially at this time. The pattern observed in the sediment thus reflects the change in the local energy consumption pattern from a predominately coal to an oil-based economy. From the plutonium profile we infer that mixing occurs for 3 or 4 years before the sediment layers are compacted.
    • Atmospheric Radiocarbon: Implications for the Geomagnetic Dipole Moment

      Sternberg, R. S.; Damon, P. E. (American Journal of Science, 1983-01-01)
    • Calibrated 14C Dates in Central Europe - Same as Elsewhere?

      Freundlich, J. C.; Schmidt, Burghart (American Journal of Science, 1983-01-01)
      14C dating results derived from an absolutely-dated 471-year tree-ring sequence from central European oak show a trend towards somewhat older dates than those for bristlecone pine tree rings of the same age, but similar to those for Egyptian historical samples. Differences visible between these trend lines are not relevant considering the standard errors proposed by Clark (1975).
    • Carbon Exchange Between Atmosphere and Oceans in a Latitude-Dependent Advection-Diffusion Model

      Kratz, Gerhard; Kohlmaier, G. H.; Siré, E. O.; Fischbach, Ursula; Broehl, Horst (American Journal of Science, 1983-01-01)
      Marine transport of inorganic and organic carbon is simulated by means of a computer model in which the oceans are divided into a high and low latitude region. Water transport (and with it carbon transport) is reproduced 1) as downwelling of surface waters at low latitudes, and 2) in general, as different depth-dependent turbulent diffusion in both deep-sea regions. The model is calibrated with pre-bomb 14C and validated against perturbations of total carbon, 13C/C- and 14C/C-ratios; it is compatible with carbon release from fossil fuels and from biogenic sources.
    • Current 14C Measurements with the University of Washington Accelerator Facility for Radioisotope Dating

      Farwell, G. W.; Grootes, P. M.; Leach, D. D.; Schmidt, F. H.; Stuiver, Minze (American Journal of Science, 1983-01-01)
      Our accelerator mass spectrometry (AMS) system shows a one-to-one relationship between sample 14C concentrations determined by AMS and by Beta-counting. Measurements of unknown samples against a standard indicate that 14C concentration measurements to better than 2% can be made. For a 30-second data collection interval in a typical run of 100 intervals, the variability of the beam injected into the accelerator is ca 2%, that of the machine transmission is ca 4%, and counting statistics give 4.7% standard deviation for a sample of 80% of modern carbon.
    • Database Management Systems, Radiocarbon, and Archaeology

      Moffett, J. C.; Webb, R. E. (American Journal of Science, 1983-01-01)
    • Dendrochronology at Belfast as a Background to High-Precision Calibration

      Baillie, M. G. L.; Pilcher, J. R.; Pearson, G. W. (American Journal of Science, 1983-01-01)
    • Dendrochronology of Bristlecone Pine: A Progress Report

      Ferguson, C. W.; Graybill, D. A. (American Journal of Science, 1983-01-01)
      Dendrochronological studies of bristlecone pine, Pinus longaeva, have produced a continuous tree-ring sequence back to 6700 BC for the White Mountains of California and to 3258 BC for east-central Nevada.
    • Detection of the 36Cl Radioisotope at the Rehovot 14UD Pelletron Accelerator

      Paul, Michael; Meirav, Oded; Henning, Walter; Kutschera, Walter; Kaim, Robert; Goldberg, Mark B.; Gerber, Jean; Hering, William; Kaufman, Aaron; Magaritz, Mordeckai (American Journal of Science, 1983-01-01)
      A program of accelerator mass spectrometry has been started at the Rehovot 14UD Pelletron Accelerator Laboratory. Part of the initial emphasis has been directed to the detection of the 36Cl radioisotope. We report here on the present status of our work and describe our experimental system. Preliminary results are presented, showing that 36Cl/Cl concentrations ranging down to 1 x 10−14 could be measured with our system.