• An International Reference Material for Radiocarbon Dating

      Mann, W. B. (American Journal of Science, 1983-01-01)
      In August 1980, the National Bureau of Standards (NBS) issued, in the form of oxalic acid, a new International Reference Material of contemporary 14C for use in radiocarbon dating laboratories. This reference material was to replace the 1975 oxalic-acid standard, supplies of which had been practically exhausted in 1978. The preparation of the new oxalic-acid standard was described in a preliminary report, as were, also, the results then available for the activity-concentration ratio of the new to the old standard obtained by a number of leading international laboratories. With the recent completion of the analysis of all results submitted by the participating laboratories, NBS plans to issue these recently calibrated samples of oxalic acid as an NBS Standard Reference Material. There is, however, no significant difference in the reported value of its activity concentration, relative to that of the 1957 standard, from that given provisionally in 1980. Subsequent to our report (Cavallo and Mann, 1980) a further measurement of relative activity concentration was reported by the Radiocarbon Laboratory of Peking University. Their value, and that also for Delta-13C, is insignificantly different from the average value of the results submitted by the eleven laboratories that participated in the international comparison organized by NBS.
    • 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.
    • 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.
    • Detection of the 36Cl Radioisotope at the Rehovot 14UD Pelletron Accelerator

      Paul, Michael; Meirav, Oded; Henning, Walter; Kutschera, Walter; Kaim, Robert; Goldberg, Mark B.; Gerber, Jean; Hering, William; Kaufman, Aaron; Magaritz, Mordeckai (American Journal of Science, 1983-01-01)
      A program of accelerator mass spectrometry has been started at the Rehovot 14UD Pelletron Accelerator Laboratory. Part of the initial emphasis has been directed to the detection of the 36Cl radioisotope. We report here on the present status of our work and describe our experimental system. Preliminary results are presented, showing that 36Cl/Cl concentrations ranging down to 1 x 10−14 could be measured with our system.
    • 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.
    • Notice to Readers and Contributors

      American Journal of Science, 1983-01-01
    • 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.
    • Dendrochronology at Belfast as a Background to High-Precision Calibration

      Baillie, M. G. L.; Pilcher, J. R.; Pearson, G. W. (American Journal of Science, 1983-01-01)
    • Distribution of Gaseous 12CO2, 13CO2, and 14CO2 in the Sub-Soil Unsaturated Zone of the Western US Great Plains

      Thorstenson, D. C.; Weeks, E. P.; Haas, Herbert; Fisher, D. W. (American Journal of Science, 1983-01-01)
      Data on the depth distribution of the major atmospheric gases and the abundance of gaseous 12CO2, 13CO2, and 14CO2 in the subsoil unsaturated zone have been obtained from several sites in the western Great Plains of the United States. Sample profiles range from land surface to depths of 50m. Although each site must be considered on an individual basis, several general statements can be made regarding the profiles. 1) Diffusion of these gaseous molecules through the unsaturated zone is an important transport mechanism. 2) As predicted by diffusion theory, depth profiles of the various isotopic species of CO2 differ substantially from one another, depending on individual sources and sinks such as root respiration and oxidation of organic carbon at depth. 3) In general, post-bomb (> 100% modern) 14C activities are not observed in the deep unsaturated zone, in contrast to diffusion model predictions. 4) In spite of generally decreasing 14C activities with depth, absolute partial pressures of 14CO2 in the subsoil unsaturated zone are 1-2 orders of magnitude higher than the partial pressure of 14CO2 in the atmosphere.
    • Technological Advances in the University of Washington Accelerator Mass Spectrometry System

      Farwell, G. W.; Grootes, P. M.; Leach, D. D.; Schmidt, F. H. (American Journal of Science, 1983-01-01)
      During the past year we have continued to work toward greater stability and flexibility in nearly all elements of our accelerator mass spectrometry (AMS) system, which is based upon an FN tandem Van de Graaff accelerator, and have carried out measurements of 14C/12C and 10Be/9Be isotopic abundance ratios in natural samples. The principal recent developments and improvements in the accelerator system and in our sample preparation techniques for carbon and beryllium are discussed, and the results of a study of 10Be cross-contamination of beryllium samples in the sputter ion source are presented.
    • Tandem Accelerator Measurements of 10Be Deposition Rates

      Nelson, D. E.; Korteling, R. G.; Southon, J. R.; Vogel, J. S.; Nowikow, I.; Ku, T. L.; Kusakabe, Masashi; Reyss, J. L. (American Journal of Science, 1983-01-01)
      A Tandem Van de Graaff accelerator has been modified for use in the direct measurement of natural abundances of 10Be and 14C. A description of the system is given and some 10Be results on oceanographic samples are discussed.
    • 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.
    • Dendrochronology of Bristlecone Pine: A Progress Report

      Ferguson, C. W.; Graybill, D. A. (American Journal of Science, 1983-01-01)
      Dendrochronological studies of bristlecone pine, Pinus longaeva, have produced a continuous tree-ring sequence back to 6700 BC for the White Mountains of California and to 3258 BC for east-central Nevada.
    • Current 14C Measurements with the University of Washington Accelerator Facility for Radioisotope Dating

      Farwell, G. W.; Grootes, P. M.; Leach, D. D.; Schmidt, F. H.; Stuiver, Minze (American Journal of Science, 1983-01-01)
      Our accelerator mass spectrometry (AMS) system shows a one-to-one relationship between sample 14C concentrations determined by AMS and by Beta-counting. Measurements of unknown samples against a standard indicate that 14C concentration measurements to better than 2% can be made. For a 30-second data collection interval in a typical run of 100 intervals, the variability of the beam injected into the accelerator is ca 2%, that of the machine transmission is ca 4%, and counting statistics give 4.7% standard deviation for a sample of 80% of modern carbon.
    • Development and Operation of the Harwell Small Counter Facility for the Measurement of 14C in Very Small Samples

      Otlet, M. L.; Huxtable, G.; Evans, C. V.; Humphreys, D. C.; Short, D. C.; Conchie, S. J. (American Journal of Science, 1983-01-01)
      The Harwell system for measuring milligram size samples using Brookhaven miniature gas counters is fully operative. It comprises 12 counters of different sizes which operate simultaneously within a single NaI crystal (300mm diameter x 300mm long) acting as an anti-coincidence guard counter. Brief details are given of the construction and commissioning of the system, including counter assembly, shield design, electronics, data capture, data analysis, and chemical processing and filling procedures. The performance of the system and an overall view of the fields of application for which the counters have important applications are discussed.
    • Direct Bone Dating in a Small CO2 Counter

      Berger, Rainer (American Journal of Science, 1983-01-01)
      A small 200ml capacity CO2 proportional counting system has been developed which uses only 100mg of carbon for complete filling. Thus, with respect to the small quantities needed, it compares favorably to dedicated accelerators at significantly lower cost. The performance of this equipment is demonstrated using a variety of samples including some human bone fragments from La Jolla which had been estimated to be 28,000 years old by aspartic acid racemization analysis.
    • Carbon Exchange Between Atmosphere and Oceans in a Latitude-Dependent Advection-Diffusion Model

      Kratz, Gerhard; Kohlmaier, G. H.; Siré, E. O.; Fischbach, Ursula; Broehl, Horst (American Journal of Science, 1983-01-01)
      Marine transport of inorganic and organic carbon is simulated by means of a computer model in which the oceans are divided into a high and low latitude region. Water transport (and with it carbon transport) is reproduced 1) as downwelling of surface waters at low latitudes, and 2) in general, as different depth-dependent turbulent diffusion in both deep-sea regions. The model is calibrated with pre-bomb 14C and validated against perturbations of total carbon, 13C/C- and 14C/C-ratios; it is compatible with carbon release from fossil fuels and from biogenic sources.
    • Database Management Systems, Radiocarbon, and Archaeology

      Moffett, J. C.; Webb, R. E. (American Journal of Science, 1983-01-01)