• 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 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.
    • Validity of 14C Ages of Carbonates in Sediments

      Chen, Yijian; Polach, Henry (American Journal of Science, 1986-01-01)
      This review is based on geologic surveys carried out in Australia and China as well as on more than 300 14C dates published in Radiocarbon. Evaluated are the origins and pathways of carbonate formation, stable isotopic composition, carbonate nodule growth rates and paleo-climatic effects. The three identified delta-13C abundance peaks are unrelated to environment and carbon source whilst 14C ages group themselves into periods corresponding to past humid warm climate. It is concluded that the major error in caliche dating is due to incorporation of old limestone whilst error on nodule dating is related to their slow growth rate. Thus, caliche antedates and nodules postdate the times of their deposition. delta-13C values cannot be used to correct for limestone or atmospheric contamination effects
    • 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.
    • 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.
    • 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.
    • The Prehistoric Expansion of Farming Into "Arctic" Norway: A Chronology Based on 14C Dating

      Johansen, Olav Sverre; Vorren, Karl-Dag (American Journal of Science, 1986-01-01)
      Palynologic and archaeologic studies using 14C dating indicate that elements of farming were introduced even further north than the Arctic Circle during the Neolithic period, ca 4000 BP. A second stage with heavier reliance on farming and with probable establishment of permanent farmsteads is dated to 2000-2500 BP.
    • 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.
    • 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.
    • 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.
    • AMS Radiocarbon Dates on Foraminifera from Deep Sea Sediments

      Andree, Michael; Oeschger, Hans; Broecker, Wallace S.; Beavan, Nancy; Mix, Alan C.; Bonani, Georges; Hofmann, Hans Jakob; Morenzoni, Elvezio; Nessi, Marzio; Suter, Martin; et al. (American Journal of Science, 1986-01-01)
      14C ages were determined on samples of foraminifera separated from cores from three areas of the tropical Pacific (Fast Pacific Rise, Oontong Java Plateau, and South China Sea). Analyses were made on four planktonic species and on mixed benthics. The purpose of the multiple analysis on planktonic species is to assess the importance of artifacts resulting from the bioturbation-abundance change couple, from the bioturbation-partial dissolution couple and from redeposition by bottom currents. The goal is to use the benthic-planktonic age difference as a means of establishing changes in deep sea ventilation rate over the past 25,000 years. Results of a part of this work are presented in this paper.
    • Annual Variations of the 14C Content of Soil CO2

      Dörr, Helmut; Münnich, K. O. (American Journal of Science, 1986-01-01)
      A 6-year and a 2-year record of 14C measurements of soil CO2 in two soils are presented and discussed. The annual 14C variation of soil CO2 is controlled by the seasonally varying contribution of root respiration and of microbial decomposition of organic matter producing soil CO2. The Delta-14C soil CO2 difference between summer and winter is ca 50 per mil in a soil where turnover of organic matter is fast (r = 2.5a) and ca 100 per mil in a soil of slow turnover (r = 60a). A simple model describing the movement and turnover of organic matter is derived, giving the depth distributions of organic carbon and of 14C. The model needs a subdivision of the carbon reservoir into at least two reservoirs with residence times of r1= 1a and r2 = 100a, respectively, and with a vertical transfer velocity in the order of 0.6mm/a.
    • 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.
    • An Intercomparison of Some AMS and Small Gas Counter Laboratories

      Burleigh, Richard; Leese, Morven; Tite, Michael (American Journal of Science, 1986-01-01)
      The performance of six laboratories with the capacity to date small samples (4 AMS and 2 small gas-counter laboratories) has been compared using 100mg samples of textiles from Ancient Egypt and Peru, with the British Museum laboratory acting as independent coordinator. This intercomparison was one of normal practices and has demonstrated that a coherent series of results can be obtained when several laboratories undertake blindfold measurements, although the occurrence of outliers emphasizes the continuing need for the dating of unusually important or controversial samples to be undertaken by a group of laboratories.
    • Routine AMS Dating of Bone and Shell Proteins

      Gillespie, Richard; Hedges, Robert E. M.; Humm, M. J. (American Journal of Science, 1986-01-01)
    • Anthropogenic Radiocarbon: Past, Present, and Future

      Povinec, Pavel; Chudý, Martin; Šivo, Alexander (American Journal of Science, 1986-01-01)
      14C is one of the most important anthropogenic radionuclides released to the environment by human activities. Weapon testing raised the 14C concentration in the atmosphere and biosphere to +100% above the natural level. This excess of atmospheric 14C at present decreases with a half-life of ca 7 years. Recently, a new source of artificially produced 14C in nuclear reactors has become important. Since 1967, the Bratislava 14C laboratory has been measuring 14C in atmospheric 14CO2 and in a variety of biospheric samples in densely populated areas and in areas close to nuclear power plants. We have been able to identify a heavy-water reactor and the pressurized water reactors as sources of anthropogenic 14C. 14C concentrations show typical seasonal variations. These data are supported by measurements of 3H and 85Kr in the same locations. Results of calculations of future levels of anthropogenic 14C in the environment due to increasing nuclear reactor installations are presented.
    • 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.
    • 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.
    • 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.