• Radiocarbon Concentration of California Aerosols

      Berger, Rainer; McJunkin, David; Johnson, Roberta (American Journal of Science, 1986-01-01)
      In this study the origin of the carbonaceous fraction of total suspended particles (TSP) in air was analyzed. While the summer data show increasing carbon concentrations in the Los Angeles air basin from west to east, in the winter high levels of carbon particles can be found over the coast. The smallest and most dangerous particle fraction is principally composed of fossil carbon.
    • Radiocarbon Dating of Lake Sediment from Two Karst Lakes in Yugoslavia

      Srdoč, Dušan; Obelić, Bogomil; Horvatinčić, Nada; Krajcar-Bronić, Ines; Marčenko, Elena; Merkt, Joseph; Wong, How Kin; Sliepčević, Adela (American Journal of Science, 1986-01-01)
      Samples of sediment cores from two lakes in the karst area of northwest Yugoslavia were analyzed. Both Lakes Kozjak and Prošće are in the Plitvice National Park, Central Croatia. 14C dating, sedimentologic, seismic, and isotopic studies, and distribution of diatoms are presented. 14C dating of lake marl revealed a uniforn sedimentation rate in Lake Prošće as opposed to Lake Kozjak. Both lake sediments belong to the Holocene period. 14C dating of lake sediment is in agreement with seismic profiles, sedimentologic analysis, and diatom frequency measurements both in an undisturbed as well as in a disturbed lake sediment.
    • Radiocarbon Dating of Sediments

      Fowler, Alison J.; Gillespie, Richard; Hedges, Robert M. (American Journal of Science, 1986-01-01)
    • Radiocarbon Dating with the University of Washington Accelerator Mass Spectrometry System

      Grootes, Pieter M.; Stuiver, Minze; Farwell, George W.; Leach, Donald D.; Schmidt, Fred H. (American Journal of Science, 1986-01-01)
      The University of Washington FN tandem accelerator mass spectrometry (AMS) system has been used in a series of 14C studies. 1) The 14C concentrations in annual growth rings for 1962, 1963, and 1964 of a Sitka spruce, each divided into ten sequential segments, were measured; a full and rapid response of tree-ring cellulose to atmospheric changes in 14CO2 is indicated, with a delay, if any, of not more than three weeks. 2) The 14C concentrations in two chemical fractions of dissolved organic carbon and in two fractions (by size) of particulate organic carbon were measured for Amazon River samples from several locations. All contain bomb carbon, but the amounts differ significantly. 3) Algae samples from lakes in the dry valleys of Antarctica were dated in order to assist in the reconstruction of the climatic history of Antarctica. 4) Background studies indicate that the contribution of the AMS system itself to the observed 14C concentrations is equivalent to an age of ca 60,000 14C yr BP; for a prepared sample of 5mg of carbon the background corresponds to ca 50,000 years.
    • Radiocarbon in Particulate Matter from the Eastern Sub-Arctic Pacific Ocean: Evidence of a Source of Terrestrial Carbon to the Deep Sea

      Druffel, Ellen R. M.; Honjo, Susumu; Griffin, Sheila; Wong, C. S. (American Journal of Science, 1986-01-01)
      Carbon isotope ratios were measured in organic and inorganic carbon of settling particulate matter collected with a sediment trap at Ocean Station "P" in the Gulf of Alaska from March to October, 1983. Dissolved inorganic carbon (DIG) in surface sea water collected during two different seasons in 1984 were analyzed using large gas proportional counters and revealed a minimum seasonal Delta-14C variation of 14 per mil. Results show that the 14C of calcium carbonate sedimenting to the deep sea is the same as that measured in surface water DIG. In contrast, particulate organic carbon (POC) had significantly higher Delta-14C values (by 25-70 per mil) than that in surface water DIG. Also, the delta-13C of the POC was markedly lower than previously reported values from other trap stations and marine particulate matter in general. Results from this study suggest that a significant amount of the POC settling to the deep sea at this pelagic station is of terrestrial origin, not strictly of marine origin as had previously been believed.
    • Regional Suess Effect in the Upper Silesia Urban Area

      Awsiuk, Romuald; Pazdur, Mieczysław F. (American Journal of Science, 1986-01-01)
      The study of a regional Suess effect is based on three sets of samples of atmospheric CO2: 1) a series of samples collected at the same site in Gliwice from 1980 to 1984, 2) samples collected simultaneously at different sites within the limits of an urban and industrial region of Upper Silesia, and 3) samples collected simultaneously outside this region along an eastern direction. Results of 14C concentration measurements show systematic decrease of Delta-14C with the rate close to the corresponding value for clean air. Depletion of 14C concentration was found to be virtually the same in the whole urban area. Analysis of regional synoptic data reveals correlation of individual Delta-14C values with wind direction, frequency of calm, and vertical stability of the atmosphere.
    • Revealing Histories of Exposure Using In Situ Produced 26Al and 10Be in Libyan Desert Glass

      Klein, Jeffrey; Giegengack, Robert; Middleton, Roy; Sharma, Pankaj; Underwood, J.; Weeks, R. A. (American Journal of Science, 1986-01-01)
      We present the results of measurements of 26Al and 10Be produced in situ in 12 samples of Libyan Desert Glass by cosmic rays during the last ten million years. Based on the variability of the concentrations of 10Be and of the 26Al/10Be ratios we measured, we conclude that individual fragments of glass have experienced different exposure histories, implying several major redistributions of the glass within the past 106 years. The 26Al and 10Be concentrations are inconsistent with the theoretical estimates of the rates of in situ production. We estimate minimum production rates of 70 atoms g-1 yr-1 and 10 atoms g-1 yr-1 for 26Al and10Be, respectively, produced in quartz at sea level between 60-90 degree latitude. Despite the present uncertainty in the rates of production, we feel that these results show clearly the effectiveness of in situ produced 26Al and10Be in studying earth-surface processes.
    • Routine AMS Dating of Bone and Shell Proteins

      Gillespie, Richard; Hedges, Robert E. M.; Humm, M. J. (American Journal of Science, 1986-01-01)
    • Secular Variations of Cosmogenic 14C on Earth: Their Discovery and Interpretation

      Suess, Hans E. (American Journal of Science, 1986-01-01)
      Measurement of 14C in samples of wood of precisely known age have shown that the cosmogenic 14C content of the CO2 in the atmosphere has not remained constant during the period of time covered by radiocarbon dating. As the terrestrial atmosphere mixes with a time constant of less than 3 years, these variations must be essentially independent of geographic location. The 14C in atmospheric CO2 must be a quantity that, at a given time, pertains to the terrestrial atmosphere as a whole. Not only is its knowledge necessary for deriving accurate radiocarbon dates, but it is also valuable in connection with many geophysical and astrophysical problems. Unfortunately, progress in our knowledge of 14C variations in the terrestrial atmosphere has been delayed by hidden experimental errors in results obtained by many laboratories. By rigorous statistical analysis of the La Jolla results, it is now possible to show that the 14C variations are not simple random fluctuations but show distinct regularities. Similar patterns of variations have been found in the growth rate of trees during the last 5000 years. Measurements of radiogenic 10Be currently being done by European workers promise to conclusively elucidate the 14C findings.
    • Standardizing Procedures for Collecting, Submitting, Recording, and Reporting Radiocarbon Samples

      Kra, Renee (American Journal of Science, 1986-01-01)
      A new radiocarbon sample record form has been compiled for consensus among radiocarbon daters and users. The form is designed to obtain comprehensive standardized documentation of radiocarbon dates for reporting and disseminating valuable data. This method of reporting 14C dates will help resolve problems which include: 1) publication of all dated samples, 2) selection of significant samples, 3) interpretation of data, 4) recognition of problematic dates, 5) maintenance of an active archive of 4C dates, and 6) implementation of an international retrieval system for dates.
    • Studies of Non-Marine Mollusks for the Selection of Shell Samples for Radiocarbon Dating

      Yates, Timothy (American Journal of Science, 1986-01-01)
      14C dating of shells from terrestrial and freshwater mollusks is prone to distortion by post-depositional diagenesis as well as incorporation of material depleted in 14C while the mollusk was alive. Three types of diagenetic change can result: etching, the development of surface crusts, and replacement of aragonite by calcite. Inspection under the light microscope, x-ray diffraction, and scanning electron microscope make it possible to assess the relative importance of the changes. When they are corrfined to the surface, mechanical cleaning combined with judicious leaching can reduce them to <1% of the total sample. The corresponding errors, which can now be specified, are often no greater than those associated with the statistics of counting.
    • The AMS Dating of Separate Fractions in Archaeology

      Batten, R. J.; Gillespie, Richard; Gowlett, J. A. J.; Hedges, Robert E. M. (American Journal of Science, 1986-01-01)
    • The Chemical Preparation of AgCl for Measuring 36Cl in Polar Ice with Accelerator Mass Spectrometry

      Conard, N. J.; Elmore, David; Kubik, P. W.; Gove, H. E.; Tubbs, L. E.; Chrunyk, B. A.; Wahlen, Martin (American Journal of Science, 1986-01-01)
      A method of chemical separation and purification of chloride from relatively small samples (500 to 2100g) of glacial ice is presented. With this procedure the first successful measurements of pre-bomb levels of 36Cl in Greenland ice have been made. Emphasis is placed on methods of reducing sulfur, which causes interference in the accelerator mass spectrometry, and in maximizing the yield. Data regarding the selection of materials for sample holders and the use of metal powders for extending the lifetime of the sample are also presented.
    • The Development of Practical Systems for 14C Measurement in Small Samples Using Miniature Counters

      Otlet, R. L.; Huxtable, George; Sanderson, D. W. (American Journal of Science, 1986-01-01)
      Miniature gas counters have been in use since the early 1960s for the measurement of 14C but were for a long time seen as suitable for providing approximate indications of activity rather than measurements for more precise dates. In recent years the need for better measurements of small samples has posed a continuing challenge for the 14C laboratories. This paper examines how the challenge has been met across the world using conventional beta decay counting techniques and proportional gas counters of 50ml volume or less. A survey is made of the rise of these techniques and attention paid to the solution through modern technology of earlier problems. Some practical systems, now in routine use, are described and consideration is given to the future for miniature counter measurements. Such systems have several attractive features that will guarantee their usefulness in 14C measurements for the future.
    • The Effects of Contamination of Calcareous Sediments on Their Radiocarbon Ages

      Srdoč, Dušan; Horvatinčić, Nada; Obelić, Bogomil; Krajcar-Bronić, Ines; O, Malley Peg (American Journal of Science, 1986-01-01)
      Two principal reasons for the inherent uncertainty in 14C dating of calcareous sediments such as tufa or those of lacustrine origin are the unknown initial 14C activity (A0) of the sediment, mainly affecting younger (Holocene) samples, and contamination of older sediments with recent carbonate, causing 14C ages to be excessively young. To assess the contamination effect, samples of old tufa from the Riss/Würm interglacial were examined. These sediments contain essentially no 14C except that contributed by surface contamination. Tufa samples were crushed and grains ranging in size from <1 mm, 1 to 2mm, up to 4 to 5mm were separated for analysis; 2M HCl was then used to dissolve the samples in successive steps. 14C measurements indicated that each subsequent soluble fraction obtained from porous tufa gave a successively older age, indicating that the surface of the sample was contaminated by younger carbonates. No consistent effect of grain size on the 14C age was observed. Compact tufa proved to be less subject to contamination. 14C ages obtained on this material were also too young, yet older than the age obtained from porous tufa samples. C ages of interglacial tufa were cross-checked with the 230Th/234U dating method, using samples of very clean calcite which overlies the tufa blocks. Inferred 230Th/234U ages of the interglacial tufa (which had yielded 14C dates ranging from 25,000 to 37,000 yr) coincided with the last interglacial (Riss/Wurm, Stage 5). Samples of Holocene tufa, in which contributions of recent 14C from surface contamination would pose less of a problem, yielded 14C and 230Th/234U dates which were in excellent agreement.
    • The ETH/SIN Dating Facility: A Status Report

      Bonani, Georges; Hofmann, Hans-Jakob; Morenzoni, Elvezio; Nessi, Marzio; Suter, Martin; Wölfli, Willy (American Journal of Science, 1986-01-01)
      The ETH/SIN AMS dating facility is routinely used for 10Be,14C, 26Al, and 36Cl measurements. The present status and performance of this facility are reviewed and some of its major applications summarized.
    • The Influence of Contaminating (Fossil) Carbonate and the Variations of delta-13C in Mortar Dating

      Van Strydonck, Mark; Dupas, Michel; Dauchot-Dehon, Michele; Pachiaudi, Christiane; Marechal, Joelle (American Journal of Science, 1986-01-01)
      The influence of the aggregate in mortar dating is examined. Sample activity as well as isotopic fractionation approach the expected values at lower yields of the preparation reaction of the counting gas. Good results are obtained at low fossil carbonate concentration. delta-13C cannot give information about this concentration but preliminary visual and chemical analysis of the mortar makes prediction of sample validity possible.
    • The Potential of the London Underground for Liquid Scintillation Counting

      Bowman, Sheridan (American Journal of Science, 1986-01-01)
      A portable gamma spectrometer has been used to survey three locations that are part of the London Underground Transport System (the "tube"). Up to an order of magnitude reduction in the cosmic ray flux was observed relative to the laboratory level. The likely reduction in background count rate achievable by underground siting of currently used Packard and LKB liquid scintillation counters is considered. It is noted that in the present, surface usage for radiocarbon dating, the background count rate of low-potassium glass vials in the LKB is not substanially higher than that of PTFE vials.
    • The Power of 14C Measurements Combined with Chemical Characterization for Tracing Urban Aerosol in Norway

      Currie, L. A.; Klouda, G. A.; Schjoldager, Jorgen; Ramdahl, Thomas (American Journal of Science, 1986-01-01)
      Changing fuel patterns and increased awareness of health effects from combustion aerosols have generated considerable interest in the use of 14C as a biogenic-fossil aerosol source discriminator. Prior studies in the US demonstrated the importance of 14C measurement for estimating the wood-burning contribution to urban aerosols. The present work treats a specific air-pollution problem in the town of Elverum, Norway where large wintertime concentrations of aerosol carbon and polycyclic aromatic hydrocarbons (PAH) were suspected to come from residential woodl combustion (RWC). The problem was significant in that up to 50 micrograms/m3[C] and 490 micrograms/m3[PAH] were found during pollution episodes. Samples collected during two winters were analyzed for C, C, PAH, and several elements in the fine fraction (<3 micrometers) aerosol. Source apportionment based on these species indicated an average of ca 65% RWC-carbon (14C), ca 5% fine particle mass from motor vehicles (Pb), but negligible contributions from heavy fuel oil (Ni, V). Patterns of 14C and total C, examined as a function of temperature and PAH, indicated large increases in RWC aerosol on the coldest days, and a major RWC contribution to the PAH fraction. Patterns with inorganic species implied multiple tracer sources, and one important case of long-range transport.