• 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 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 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 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 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 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.
    • Radioisotope Dating with the ETHZ-EN-Tandem Accelerator

      Wölfli, Willy; Bonani, Georges; Suter, Martin; Balzer, Richard; Nessi, Marzio; Stoller, Christian; Beer, Jürg; Oeschger, Hans; Andrée, Michael (American Journal of Science, 1983-01-01)
    • 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.
    • Results of Tests and Measurements from the NSF Regional Accelerator Facility for Radioisotope Dating

      Donahue, D. J.; Zabel, T. H.; Jull, A. J. T.; Damon, P. E.; Purser, K. H. (American Journal of Science, 1983-01-01)
      Tests of performance of the tandem accelerator mass spectrometer at the NSF Regional Facility at the University of Arizona are discussed. Results of measurements on some tree rings and on some archaeologic samples are presented.
    • Sample Chemistry for the Oxford High Energy Mass Spectrometer

      Gillespie, Richard; Hedges, Robert E. M. (American Journal of Science, 1983-01-01)
      Chemical pretreatment procedures for the decontamination, extraction, and isolation of organic materials for 14C dating using the Oxford accelerator system are described. Specific details are given for the isolation and chromatographic purification of amino acids from bone and tooth collagen, of lipids from sediments, and of cellulose and glucose from wood, paper, and textiles. A description is also given of the apparatus used for the routine preparation of 1 to 5mg graphite samples on tantalum wire, for use in the accelerator ion source. The high energy mass spectrometer (HEMS) approach to 14C dating allows the use of very small samples in the low milligram range. Sample pretreatment and decontamination procedures can be both more vigorous and more selective than those used by conventional dating laboratories. Specific chemical compounds can be isolated from archaeologic or geologic samples; such compounds may be characteristic of particular source materials and, hence, provide more detailed information than is generally possible using bulk organic samples. The Oxford Radiocarbon Unit has concentrated on three sample types that represent the kind of material we expect to work on initially: bone, lake sediment, and wood.
    • Short-Term Variations in Radiocarbon Concentration with the 11-Year Solar Cycle

      Povinec, Pavel; Burchuladze, A. A.; Pagava, S. V. (American Journal of Science, 1983-01-01)
      Previous investigations on short-term 14C variations in tree rings are compared with 14C measurements in wine samples. The comparison is made for 4 solar cycles (1903-1944) with the same method of statistical evaluation of measured results. The average amplitude of Delta-14 variations as observed by various authors in tree-ring samples is ca 2 +/1 per mil; however, wine samples show an average amplitude of 4.3 +/1.6 per mil. The anticorrelation dependence of Delta-14C on Wolf sunspot numbers was observed with a time shift between W maxima and Delta-14C minima of 3-5 yr for different solar cycles.
    • Stable Isotope Fractionation During Benzene Synthesis for Radiocarbon Dating

      Panarello, Hector O.; Albero, Miguel C.; Angiolini, Fernando E. (American Journal of Science, 1983-01-01)
      13C isotope analyses of different stages of benzene synthesis have been made to study partial isotope fractionation. More than 60 analyses of carbonates, charcoal, carbon dioxide, and benzene were made in a double collector mass spectrometer. In the first stage of the synthesis (conversion to carbon dioxide) little or no fractionation was observed, beyond the analytical error of the method. Later stages of the process, show a greater and systematic fractionation. The experimental techniques are described.
    • Statistics of the AD Record of Climatic and Carbon Isotopic Change

      Stuiver, Minze (American Journal of Science, 1983-01-01)
      The AD time series of Delta-14C, delta-13C, and cosmic ray fluxes, Q, were analyzed for similarities. Two cases of significant correlation between Q and tree-ring delta-13C were encountered, for which up to 25% of the variance can be attributed to changes in the tree's isotope fractionation that related to solar induced climatic changes. However, it is possible that the demonstrated correlation is fortuitous because actual climate proxy records generally do not correlate significantly with the Q record.
    • Studies on Holocene Geochronology of the Coastal Region of Southern Fujian, China

      Chenghui, Chen; Huang, Baolin; Mingliang, Wang (American Journal of Science, 1983-01-01)
      Our studies on 14C chronology and palynology of Holocene sediments in southern Fujian along the western coast of the Taiwan Straits show that the natural environment has undergone three stages of development during the Holocene. From Early Holocene (ca 10,000–8000 yr ago) to Middle Holocene (8000–2500 yr ago) and then to Late Holocene (2500 yr ago), sediments varied from land-sea transitional to marine and then to terrigenous; vegetation altered from mixed forest to evergreen broad-leaf forest and then steppe; climate fluctuated from temperate to hot and then to warm. The sea-level maximum in the post-glacial period occurred at 5000–6000 yr ago, at 5 to 10m elevation. During the subsequent regression, two stable stages of sea-level dated at >3000 and ca 2000 yr ago. The climatic drying and eolian sand deposit began at 700 yr ago. The results agree with our previous studies in southern Liaoning.
    • Survey of Simple Carbon Compounds for Use in a Negative Ion Sputter Source

      Vogel, J. S.; Nowikow, I. G.; Southon, J. R.; Nelson, D. E. (American Journal of Science, 1983-01-01)
      We present a survey of carbon beam yields from 20 simple carbon compounds using a caesium sputter source and the McMaster University tandem accelerator. The carbon yield was measured as a 35MeV 12C4+ beam. We found that the beam intensities could be related to a grouping of the carbides according to the chemical bonding of the compounds. The usefulness of the compounds for accelerator 14C dating was further related to their preparation chemistries. Strontium carbide was the equal of graphite in negative carbon ion beam production and aluminum carbide was found to be a good candidate for further tests because of its good sputter yield and preparation chemistry. Charcoal was also tested with varying amounts of silver added as a heat conduction aid.