• 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)
    • 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.
    • Radiocarbon Dating of Millimole-Sized Gaseous Samples

      Srdoč, Dušan; Obelić, Bogomil; Horvatinčić, Nada (American Journal of Science, 1983-01-01)
      As an alternative to the accelerator technique, a simple, compact, small counter system has been developed and tested for routine 14C dating. Our small counter is an all-metal design made of the OFHC copper with quartz supports for the anode (25 micrometers stainless steel). Careful selection of materials for the counter construction was made based on the measurements of the alpha contamination. Methane as the counter filling gave better resolution and gas gain stability, whereas CO2 gave lower background counting rate and it was easier to prepare and to handle. The long term run using CH4 showed that the gas gain remained stable within 1-2% for months after the initial drop which followed the counter filling. A 7-day counting period was sufficient to achieve a 3% relative standard deviation which was considered acceptable for routine dating of younger samples.
    • Radiocarbon Dating of Tufa in Paleoclimatic Studies

      Srdoč, Dušan; Horvatinčić, Nada; Obelić, Bogomil; Sliepčević, Adela (American Journal of Science, 1983-01-01)
      Calcareous deposits known as tufa or travertine contain biogenic carbon and are a potential source of geochronologic information. Many dated samples from Karstic regions in Yugoslavia proved that 14C analyses of tufa can provide reliable data reflecting climatic conditions in the past. Systematic dating of tufa samples revealed two distinct groups of deposits: recent tufa deposits, with a sharp age limit of ∼6000 +/- 500 years BP, and old tufa deposits with 14C age ranges from 25,000 +/- 2300 years BP to the lowest limit of our 14C dating system (∼37,000 years). A histogram based on the initial activity AO = 0.85 shows the age distribution of randomly sampled tufas vs sample frequency. A time gap between ∼6000 BP and ∼23,000 BP is evident, reflecting cooler climatic conditions. The start of peat deposition is coincident with that of tufa growth in the Holocene. Paleoclimatic implications of tufa growth periods obtained by 14C dating are as follows: climatic conditions that favor tufa formation at least in karstic regions, are very stringent. Therefore, climatic conditions, such as mean annual temperature and humidity, as well as hydrologic and vegetational conditions, must have been very similar in periods of tufa growth. While recent tufa deposits are coincident with the warm Holocene period, old tufa can be associated with warm interstadials in the Würm.
    • Radiocarbon Dating of Fossil Eggshell

      Long, Austin; Hendershott, Richard; Martin, P. S. (American Journal of Science, 1983-01-01)
      Controlled feeding experiments demonstrate that the 14C content of the carbonate fraction of fossil avian eggshell should reliably reflect the 14C activity of feed and contemporary atmospheric CO2 regardless of amounts of 14C depleted scratch injested. Consideration of biochemical pathways and exchange rates across lung membranes leads to the possibility that the carbonate fraction may, in some instances, be slightly 14C depleted. 14C dates on eggshell carbonate should require little or no correction. As with marine shell carbonate, normal soil-forming processes may alter the surficial carbon isotopes in eggshell carbonate. 14C dates on the protein fraction should be even more reliable than those on the carbonate fraction, but only if special precautions or separation techniques exclude non-indigenous carbon from the sample. Original protein contents are likely to be too low for conventional 14C dating techniques.
    • 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)
    • Radiocarbon Dating in the Arctic Region

      Olsson, Ingrid U. (American Journal of Science, 1983-01-01)
    • 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.
    • Production of C- Directly from CO2 Using the ANIS Sputter Source

      Heinemeier, Jan; Andersen, Hans Henrik (American Journal of Science, 1983-01-01)
      Micro-ampere beams of C- have been produced with the Aarhus negative-ion source, operated on CO2 gas. The efficiency of the source and memory effects have been measured, using 13C-enriched CO2, in order to evaluate the applicability of the source to 14C dating by accelerator mass spectroscopy.
    • Participants

      American Journal of Science, 1983-01-01
    • Possibilities in the Dating of Writing Materials and Textiles

      Burleigh, Richard; Baynes-Cope, A. D. (American Journal of Science, 1983-01-01)
    • Possible Depletion in 14C in Trees Growing in Calcareous Soils

      Tauber, Henrik (American Journal of Science, 1983-01-01)
      14C activities of decadal samples from beech trees growing under extreme calcareous conditions were compared to 14C activities of decadal samples of the same age from a beech tree growing in a normal mold soil in order to see whether part of the carbon assimilated during photosynthesis might originate from 14C-deficient carbonates in the soil. The calcareous soils contained from 18 to 52% calcium carbonate, and this carbonate had a mean 14C age of 10,200 to 17,600 years BP. A comparison was also made with the 14C activity of contemporaneous samples from Douglas Fir from the US North Pacific (Stuiver, 1982). No significant depletion in 14C activity in beech trees growing in the highly calcareous soils was detected. The measured mean difference in 14C activity in beech trees from calcareous and non-calcareous sites corresponds to an uptake of 0.12 +/- 0.3% carbon from soil carbonates in the calcareous sites.
    • 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.
    • On a 50-Year "Climate-Free" delta-13C Record from Juniper Tree Rings

      Leavitt, Steven W.; Long, Austin (American Journal of Science, 1983-01-01)
    • Moscow MV Lomonosov State University Radiocarbon Dates II: Sea Level Indicators from Coastal USSR

      Glushankova, N. I.; Parnunin, O. B.; Selivanov, A. O.; Shlukov, A. I.; Timashkova, T. A. (American Journal of Science, 1983-01-01)
    • Miniature Signals and Miniature Counters: Accuracy Assurance Via Microprocessors and Multiparameter Control Techniques

      Currie, L. A.; Gerlach, R. W.; Klouda, G. A.; Ruegg, F. C.; Tompkins, G. B. (American Journal of Science, 1983-01-01)
      When 14C signals approach background levels, the validity of assumptions concerning Poisson counting statistics and measurement system stability becomes crucial in interpreting the resultant low-level counting observations. This has been demonstrated in our previous work on detection limits for non-Poisson error and it is critical in our current studies of carbonaceous pollutants, where the 14C signal from just 5 mg C is comparable to that of the background for our miniature gas proportional counters. To assure data quality, our multi-detector system is designed for the on-line monitoring of critical parameters that reflect both the (statistical) nature of the non-Poisson errors and the underlying (physical) causes. It sends >60 bits of information/pulse to a microprocessor which automatically generates, for each counting period, two-dimensional spectra and multiparameter correlation and control charts. To evaluate the validity of long-term counting of 1–10 mg C we use robust (statistical) estimators, optimal counting interval subdivision, and time series analysis of the individual pulses. New opportunities for selective sampling and chemical fractionation which come with the small sample measurement capability have led us to give special attention also to higher control levels, involving e g, isotonic heterogeneity and representative standard materials.
    • Modeling of Atmospheric Radiocarbon Fluctuations for the Past Three Centuries

      Damon, P. E.; Sternberg, R. S.; Radnell, C. J. (American Journal of Science, 1983-01-01)