• On the Origin of Carbonaceous Particles in American Cities: Results of Radiocarbon "Dating" and Chemical Characterization

      Currie, L. A.; Klouda, G. A.; Continetti, R. E.; Kaplan, I. R.; Wong, W. W. W.; Dubay, G. W.; Stevens, R. K. (American Journal of Science, 1983-01-01)
      During the past three years radiocarbon assay has emerged as a primary tool in the quantitative assignment of sources of urban and rural particulate pollution. Its use in several major field studies has come about because of its excellent (fossil/biogenic) discriminating power, because of advances in 14C measurements of small samples, and because of the increased significance of carbonaceous particles in the atmosphere. The problem is especially important in the cities, where increased concentrations of fine particles lead to pollution episodes characterized by poor visibility and changes in the radiation balance (absorption, scattering), and immediate and possibly long-term health effects. Efforts in source apportionment in such affected areas have been based on emissions inventories, dispersion modeling, and receptor modeling – ie, chemical and physical (and statistical) characterization of particles collected at designated receptor sites. It is in the last category that 14C has become quite effective in helping to resolve particle sources. Results are presented for studies carried out in Los Angeles, Denver, and Houston which incorporated 14C measurements, inorganic and organic chemical characterization, and receptor modeling. The 14C data indicated wide ranging contributions of biogenic and fossil carbon sources – eg, <10% to 60% contemporary (biogenic) in Houston – depending on meteorological, biological, and anthropological activity. The combined (chemical, isotopic, statistical) data point to sources such as vehicles, wood combustion, power plants, and vegetation.
    • Non-Concordance of Radiocarbon and Amino Acid Racemization: Deduced Age Estimates on Human Bone: Implications for the Dating of the Earliest Homo Sapiens in the New World

      Taylor, R. E. (American Journal of Science, 1983-01-01)
      Radiocarbon determinations, employing both decay and direct counting, were obtained on various organic fractions of four human skeletal samples previously assigned ages ranging from 28,000 to 70,000 years on the basis of their D/L aspartic acid racemization values. In all four cases, the 14C values require an order of magnitude reduction in age.
    • Radiocarbon Database: A Pilot Project

      Gulliksen, Steinar (American Journal of Science, 1983-01-01)
      Computer storage and surveys of large sets of data should be an attractive technique for users of 14C dates. Our pilot project demonstrates the effectiveness of a text retrieval system, NOVA STATUS. A small database comprising ca 100 dates, selected from results of the Trondheim 14C laboratory, is generated. Data entry to the computer is made by feeding typewritten forms through a document reader capable of optical character recognition. A text retrieval system allows data input to be in a flexible format. Program systems for text retrieval are in common use and easily implemented for a 14C database.
    • Radiocarbon Activity Variation in Dated Tree Rings Grown in Mackenzie Delta

      Fan, C. Y.; Tie-Mei, Chen; Si-Xun, Yun; Kai-Mei, Dai (American Journal of Science, 1983-01-01)
      Forty-five tree rings (1881-1925) were taken from a white spruce grown near Campbell River in Mackenzie Delta, Canada, for the measurement of 14C activity variation. Because of the narrowness of the rings, 2 and sometimes 3 rings were combined to yield a total of 21 specimens. The 14C content in these specimens was measured with a liquid scintillation-PM tube counter system of the History Department of Peking University. The data points exhibit a 10 per mil variation, anti-correlated with sunspot numbers. The physical implication is discussed.
    • Radiocarbon Dating Archaeologic and Environmental Samples Containing 10 to 120 Milligrams of Carbon

      Sheppard, John C.; Hopper, J. Fred; Welter, Yvonne (American Journal of Science, 1983-01-01)
    • 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 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)
    • Radiocarbon Dating with the Utrecht Tandem Accelerator

      van der Borg, K.; Hoogenboom, J. A.; Jelmersma, R. A.; Vermeer, Abraham; Hut, Gert (American Journal of Science, 1983-01-01)
    • 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.
    • Radiocarbon Measurements of Particulates in Smog

      Berger, Rainer; Johnson, R. M.; Holmes, J. R. (American Journal of Science, 1983-01-01)
      In recent years in California, smog aerosols have been observed in metropolitan and rural areas. We wondered what the relative contribution is from sources such as fossil fuel combustion (eg, cars, factories) and emissions from trees and other plants. Pollution produced by fossil fuel combustion can be distinguished from biological sources using radioactive carbon. Carbon in fossil organic materials is radioactively dead whereas carbon in living plants contains 14C. Smog particles were collected on clean glass or quartz fiber paper and analyzed in a small volume CO2 proportional counter for 14C content. Results are given for sampling locations at UCLA, El Monte, Riverside, and Lake Tahoe showing the relative contributions of fossil and modern carbon sources ranging from 0 to 74% and 26 to 100% respectively.
    • Temporal 10Be Variations in Ice

      Beer, Jürg; Andree, Michael; Oeschger, Hans; Stauffer, Bernhard; Balzer, Richard; Bonani, Georges; Stoller, Christian; Suter, Martin; Wölfli, Willy; Finkel, Robert C. (American Journal of Science, 1983-01-01)
    • Evaluation of Direct-Precipitation and Gas-Evolution Methods for Radiocarbon Dating of Ground Water

      Yang, In Che (American Journal of Science, 1983-01-01)
      The extraction of dissolved carbonate species for age dating from a 100L water sample by the direct-precipitation method (DPM) and by the gas-evolution method (GEM) has been investigated. Stable carbon-isotope fractionation between initial and final carbon dioxide evolved was ca 11 per mil by GEM and 1 per mil by DPM. GEM will produce isotopically lighter carbon dioxide compared with DPM if carbonate recovery is low. Extraction efficiency of > 95% can be achieved by GEM in 3 hours using nitrogen gas at a sweeping rate of 2000cc per minute. DPM requires precipitates to settle overnight to assure > 95% recovery. GEM is little affected by a high concentration of sulfate ions, whereas DPM is greatly affected by sulfate resulting in less yield.
    • The Oxford Radiocarbon Accelerator Facility

      Gillespie, Richard; Hedges, R. E. M.; White, N. R. (American Journal of Science, 1983-01-01)
    • The Integration of Radiocarbon Dating in Archaeology

      Waterbolk, H. T. (American Journal of Science, 1983-01-01)
    • The Radon Problem in 14C Dating

      Nydal, Reidar (American Journal of Science, 1983-01-01)
      Due to traces of radium and uranium in most 14C samples, radon appears as a radioactive contamination in the CO2 prepared by combustion. This contamination must be removed by an active purification prodecure or by storing the CO2 prior to measurement. No effective electronic discrimination against radon and its daughter elements can be performed. The necessary storage time until radon has decayed varies widely, especially for marine shells. The latter material, collected from Norway and Svalbard, has been a main object for the present investigation. In a few cases, a measureable amount of radon may be left even after eight weeks. The behavior of radon and its daughter elements in a CO2 proportional counter has been studied.
    • 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.
    • Recent 14C Measurements with the Chalk River Tandem Accelerator

      Brown, R. M.; Andrews, H. R.; Ball, G. C.; Burn, Neil; Davies, W. G.; Imahori, Yoshio; Milton, J. C. D.; Workman, Wayne (American Journal of Science, 1983-01-01)
      The Chalk River Tandem Accelerator Mass Spectrometry System has reached a state of reliable measurement of 14C using 2 to 5mg elemental carbon prepared by Mg reduction of CO2. For two comparisons of a near-modern unknown with the NBS oxalic acid standard we obtain a total error of ∼ +/- 4.5%, consisting of a random system error of about +/- 3.5% combined with the statistical counting error. Measurements have been made on 70 samples in 30 days of running time during the past year. Samples included deep rock carbonates, cosmogenic 14C in meteorites, charcoal from earthquake fault zones, collagen of bone artifacts and fossil beetle-fragments.