• 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.
    • Applications of the Use of Hawthorn Berries in Monitoring 14C Emissions from a UK Nuclear Establishment Over an Extended Period

      Walker, A. J.; Otlet, R. L.; Longley, Harry (American Journal of Science, 1986-01-01)
      The paper describes a study undertaken to examine the dispersion pattern of gaseous emissions, as indicated by 14C uptake in natural materials, around the nuclear reprocessing plant at Sellafield, Cumbria, UK. The extent and directional dispersion of the released 14C is established and its variability over an extended period assessed. Results of measurements taken during three sampling seasons (1981,1982,1983) of the 14C activity in hawthorn berries collected over a wide area are presented and the dispersion pattern contours constructed from them are examined. Only limited agreement of the results with the theoretical relationship 1/r is found and both meteorology and topography are seen to be important in determining the shape of the observed patterns.
    • 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).
    • 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.
    • 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.
    • 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.
    • 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.
    • 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 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 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.
    • Urban Atmospheric 14CO and 14CH4 Measurements by Accelerator Mass Spectrometry

      Klouda, G. A.; Currie, L. A.; Donahue, D. J.; Jull, A. J. T.; Naylor, M. H. (American Journal of Science, 1986-01-01)
      Atmospheric gas samples (0.1 m3) were collected at ground level during January/February 1984 in Las Vegas, Nevada for 14C/13C accelerator mass spectrometry and total abundance measurements of CO and CH4. During winter months in this locale, CO concentrations can occur at 10 to 100 times background, occasionally exceeding the National Ambient Air Quality Standard (NAAQS). Methane concentrations show a slight enhancement (-24%) above the background (non-urban troposphere) level. A comparison of CO and CH4 concentrations shows a good linear correlation which may indicate a common source. Preliminary 14C/13C results of the two species suggest that fossil emissions are the predominant source of excess CO and CH4 in the samples taken. Estimates of anthropogemc CO and CH4 are important for source apportionment of combustion emissions. In addition, this information is valuable for understanding the global CO and CH4 cycles and, therefore, human impact on climate and the stratospheric ozone layer.