• Saclay Natural Radiocarbon Measurements I

      Delibrias, G.; Guillier, M. T.; Labeyrie, J. (American Journal of Science, 1964-01-01)
    • Saclay Natural Radiocarbon Measurements II

      Delibrias, G.; Guillier, M. T.; Labeyrie, J. (American Journal of Science, 1965-01-01)
    • 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.
    • Sample Credentials Necessary for Meaningful High-Precision 14C Dating

      Jope, E. M. (American Journal of Science, 1986-01-01)
      Samples presented for high-precision 14C dating must satisfy stringent requirements if the 14C determinations are to yield meaningful sharp calendric dates, such as are now possible with the bidecadal high-precision calibration curve. The total carbon content should come from a confined time range 10-20 years (10-20 tree rings in wood or charcoal) appropriate for the bidecadal calibration curve. For accurate calendric dating the relation of these rings to the outer growth rings must be known. Application of the high-precision calibration curve to some archaeologic examples is discussed. It is now up to archaeologists and geoscientists to use this refined chronometric instrument to fullest advantage.
    • Sample Dilution for AMS 14C Analysis of Small Samples (30-150 μg C)

      de Rooij, M.; van der Plicht, J.; Meijer, H. J. (Department of Geosciences, The University of Arizona, 2008-01-01)
      We investigated sample dilution as a technique for accelerator mass spectrometry (AMS) radiocarbon analysis of very small samples (down to 30 mu-g). By diluting such samples up to a total weight of 200 mu-g, we can still perform reliable AMS measurements and improve the success rate significantly for targets that are difficult to measure. A disadvantage of this dilution technique is a loss of measurement precision. In addition, calculations of the 14C/12C isotope ratios and the uncertainties therein are not straightforward because of peculiarities in isotope fractionation processes in the AMS system. Therefore, to make sample dilution a routine method in our laboratory, we did extensive theoretical and experimental research to find the optimum conditions for all relevant parameters. Here, we report on the first detailed study dealing with all aspects of sample dilution. Our results can be applied in general. As an illustrative test case, we analyze 14C data for CO2 extracted from an ice core, from which samples of 35 mu-g C or less are available.
    • Sample Preparation of Dissolved Organic Carbon in Groundwater for AMS 14C Analysis

      Burr, George S.; Thomas, J. M.; Reines, D.; Jeffrey, D.; Courtney, C.; Jull, A. J. Timothy; Lange, Todd (Department of Geosciences, The University of Arizona, 2001-01-01)
      This study describes a sample preparation technique used to isolate dissolved organic carbon (DOC) in groundwater for radiocarbon analysis using accelerator mass spectrometry (AMS). The goal of the work is to improve our ability to determine groundwater residence times based on 14C measurements of the DOC fraction in groundwater. Water samples were collected from carbonate and volcanic rock aquifers in southern Nevada. Multiple measurements of total dissolved organic carbon (TDOC) in groundwater from one site are used to demonstrate the reproducibility of the analytical procedure. The reproducibility of the method is about one percent (1sigma) for a 0.5 mg sample. The procedural blank for the same size sample contains about 1 percent modern carbon (pMC).
    • Sample Throughput and Data Quality at the Leibniz-Labor AMS Facility

      Nadeau, M.-J.; Grootes, P. M.; Schleicher, Markus; Hasselberg, Peter; Rieck, Anke; Bitterling, Malte (Department of Geosciences, The University of Arizona, 1998-01-01)
      Since our first report on the performance of the Kiel accelerator mass spectrometry (AMS) system and our early work on sample preparation, systems have been built to improve the sample quality and throughput of the laboratory. Minor modifications were also made on the AMS system, mainly in order to reduce the amount of work and time needed to maintain the system in optimal condition. The design and performance of a 20-port reduction system, a pneumatic target press, and a remote alarm unit for the AMS system are discussed, along with an overview of the results obtained during the last year and the procedure used to obtain them. Statistical analysis shows that the contribution of the AMS system to the measuring uncertainty at our current level (0.3% for a modern sample) is negligible.
    • Sampling Iron for Radiocarbon Dating: Influence of Modern Steel Tools on 14C Dating of Ancient Iron Artifacts

      Hüls, Matthias; Grootes, Pieter M.; Nadeau, Marie-Josée (Department of Geosciences, The University of Arizona, 2011-01-01)
      Before the 17th century, charcoal was regularly used in the production of iron (smelting and forging) and some of this charcoal carbon was incorporated into the iron. Depending on the age of the wood used to produce the charcoal, the age of the carbon incorporated in the iron lattice can reflect the age of manufacture of the iron artifacts. A reliable preparation method allowing for the routine dating of iron artifacts would permit the dating of numerous objects for which now the age can only be estimated. In an earlier work (Hls et al. 2004), we tested the extraction of carbon from iron samples by closed-tube combustion. The samples were cut in small pieces to ease the release of the carbon from the lattice. During the tests, it became clear that the steel tools used to cut the samples can add contamination at the surface. As modern steel is made using coal, this leads to erroneously old ages. We have tested ways to reduce or eliminate this surface contamination from the sampling tools using iron artifacts of known ages. In order to quantify the contamination, we produced standard test materials from pure iron (99.998% Fe) melted with carbon of known 14C content and prepared samples using different cutting tools. The results of these tests indicate that the proper choice of cutting technique and tool, combined with an additional cleaning of the freshly cut surface, reduces sample contaminations to low levels; measured sample 14C concentrations are close to the 14C content of the charcoal used to produce these standard iron samples.
    • Santa Fe Workshop Abstracts

      Department of Geosciences, The University of Arizona, 1996-01-01
    • Scandinavian Models: Radiocarbon Dates and the Origin and Spreading of Passage Graves in Sweden and Denmark

      Paulsson, Bettina Schulz (Department of Geosciences, The University of Arizona, 2010-01-01)
      Approximately 2700 radiocarbon results are currently available from European megalithic contexts. The interpretation of these 14C dates is often difficult. It is not easy to connect many of them from their archaeological context to the construction or the burial phase of the graves. This paper focuses on the megaliths of Scandinavia--a special megalith region--as it is the only place in Europe with 14C dates directly referable to the construction of the passage graves, the graves have good bone preservation, and new dating sequences are available. Some 188 14C results are now available from Scandinavian passage graves. In Sweden, new data suggest that these graves were built from the first half of the 35th century BC onwards. The 14C dates from birch bark as filling material between dry walls make it possible to build a sequence for the construction phase of the passage graves in Denmark from the 33rd century BC onward. With an interpretative Bayesian statistical framework, it is possible to untangle the nuances of the differences for the origin and the spreading of the megaliths in the different regions, to define, together with the archaeological remains, possible cultural-historical processes behind these phenomena and to discuss diffusion versus convergence.
    • Scintillation Cocktail Optimization for 14C Dating Using the Packard 2000CA/LL and 2260XL

      Anderson, Robert; Cook, G. T. (Department of Geosciences, The University of Arizona, 1991-01-01)
      In terms of both quenching and, in particular, counting efficiency, scintillation counters employing burst counting circuitry are sensitive to changes in scintillant concentration. Our research demonstrates that there are plateau regions where neither parameter is significantly influenced by moderate changes in a cocktail containing butyl PBD and bis MSB. One of these, consisting of butyl PBD 2.8mg.g-1 and bis MSB 3mg.g-1 of benzene is recommended for these counters, as it enables open window counting efficiencies of ca 90% while exhibiting optimal resistance to quenching. A method for accurate dispensing of such small weights is also described.
    • Scintillation Counter Performance at the SMU Radiocarbon Laboratory

      Devine, James M.; Haas, Herbert (American Journal of Science, 1987-01-01)
      Results are presented of a study of counter performance and vial characteristics for three liquid scintillation counters used at the SMU Radiocarbon Laboratory: the Intertechnique LS20, Packard Tri-Garb 460C, and LKB Wallac Rack Beta 1217. Modifications to photomultiplier tube high voltage, pre-amplifier gain, energy window settings, counting vial design, and sample holder design have resulted in reduced background, higher counting efficiency, and greater long-term stability for the Intertechnique and Packard counters. Square quartz counting vials are used in the Intertechnique and Packard counters with excellent results. Use of Teflon vials in the LKB counter requires careful cleaning procedures and long counting times.
    • Scottish Universities Research and Reactor Centre Radiocarbon Measurements I

      Harkness, D. D.; Wilson, H. W. (American Journal of Science, 1973-01-01)
    • Scottish Universities Research and Reactor Centre Radiocarbon Measurements II

      Harkness, D. D.; Wilson, H. W. (American Journal of Science, 1974-01-01)
    • Scottish Universities Research and Reactor Centre Radiocarbon Measurements III

      Harkness, D. D.; Wilson, H. W. (American Journal of Science, 1979-01-01)
    • Scottish Universities Research and Reactor Centre Radiocarbon Measurements IV

      Harkness, D. D. (American Journal of Science, 1981-01-01)
    • Search for Pedogenic Phases During Younger Pleistocene and Holocene (Soltanien and Rharbien) of Tunisia

      Scharpenseel, H. W.; Zakosek, Heinrich; Neue, Ulrich; Schiffmann, Heinrich (American Journal of Science, 1980-01-01)
      Radiocarbon dates, obtained from paleosols, sediments, fossils, and groundwater samples of North Africa and especially, Tunisia, were investigated for information on phases of pedogenesis throughout the younger Pleistocene and Holocene in north and central Tunisia. This paper evaluates available data, while a larger set of new samples is under study, which, hopefully will exhaust the problem and will reveal whether extrapolations such as those made in this paper, eg, phases of pedogenesis from groundwater data, are correct. Frequency distribution of the dates from groundwaters taken by systematic sampling, as well as from random soil samples from open pits that yielded access to buried paleosols, indicate that organic matter was being produced for 7 or 8 periods. The evidence suggests major pedogenic activity at about 2000 BP, 4000 to 6004 BP, 8000 to 12,000 BP, and perhaps 21,000 to 25,000 BP.
    • Searching Solar Periodicities in the Late Glacial Record of Atmospheric Radiocarbon

      Goslar, Tomasz; Tisnérat,-Laborde, Nadine; Paterne, Martine (Department of Geosciences, The University of Arizona, 2001-01-01)
      Accelerator mass spectrometry radiocarbon (AMS 14C) dating of the late glacial section of laminated sediments from Lake Gościąż and Lake Perespilno, Poland, performed with time resolution of 20-30 years suggests quasi-periodic oscillations of Delta-14C. The regularity of oscillations has been checked by the Maximum Entropy and Fast Fourier Transform methods (MEM and FFT), which revealed peaks at 200 and 230 yr. These periods are similar to those found in the high-precision Holocene Delta-14C record, and attributed to the changing sun. The analytical assessment of the significance of the FFT and MEM peaks is problematic because of non-uniform spacing and various uncertainties in the input data. The significance of the peaks has therefore been studied by the Monte-Carlo method. Because the original data were approximated with a spline function, the amplitude of the MEM and FFT peaks depends on the stiffness of the spline, which is strongly related to the "real" uncertainty of 14C ages. The Monte-Carlo experiments demonstrate that the significance levels of the MEM and FFT peaks also depend on the spline stiffness. Therefore, the existence of solar 14C variations in the Late Glacial remains an open question.
    • Seasonal and Secular Variations of Atmospheric 14CO2 Over the Western Pacific Since 1994

      Kitagawa, H.; Mukai, Hitoshi; Nojiri, Yukihiro; Shibata, Yasuyuki; Kobayashi, Toshiyuki; Nojiri, Tomoko (Department of Geosciences, The University of Arizona, 2004-01-01)
      Air sample collections over the western Pacific have continued since 1992 as a part of Center for Global Environmental Research, National Institute for Environmental Studies (CGER-NIES) global environmental monitoring program. The air samples collected on the Japan-Australia transect made it possible to trace the seasonal and secular 14CO2 variations, as well as an increasing trend of greenhouse gases over the western Pacific. A subset of CO2 samples from latitudes of 10-15 degrees N and 23-28 degrees S were chosen for accelerator mass spectrometry (AMS) 14C analysis using a NIES-TERRA AMS with a 0.3-0.4% precision. These 14CO2 records in maritime air show seasonal variations superimposed on normal exponential decreasing trends with a time constant of about 16 yr. The Delta-14C values in the Northern Hemisphere are lower those in the Southern Hemisphere by 3-4 per mil during 1994-2002. The Northern Hemisphere record shows relatively high seasonality (2.3 +/1.5 per mil) as compared with the Southern Hemisphere (1.3 +/1.2 per mil). The maximum values of seasonal cycles appear in late autumn and early winter in the Northern and Southern Hemispheres, respectively. Oscillations of 1-10 yr over the western Pacific are found to correlate possibly with the El Nino/Southern Oscillation (ENSO) events.
    • Seasonal Fluctuation of Stable Carbon Isotopic Composition in Japanese Cypress Tree Rings from the Last Glacial Period—Possibility of Paleoenvironment Reconstruction

      Takahashi, Hiroshi Aoki; Yonenobu, Hitoshi; Nakamura, Toshio; Wada, Hideki (Department of Geosciences, The University of Arizona, 2001-01-01)
      Seasonal variations of delta-13C were analyzed for two Japanese cypress trees (Chamaecyparis obtusa), one buried and one living. Both trees were different in age but sampled in areas geographically close to each other in central Japan. A buried cypress with 394 annual rings was excavated from Old Fuji mudflow, the last glacial strata of the dormant Mt. Fuji volcano. The accelerator mass spectrometry (AMS) radiocarbon date of this glacial sample was 18,600 +/120 BP (NUTA-4884). A living tree stem, which has 192 rings, was cut from the Izu Peninsula in 1986. In order to measure the seasonal delta-13C fluctuation, the tree rings were divided equally into three earlywood and one or two latewood consecutive sections. The delta-13C value within an annual ring generally increased from the first to the third or fourth sections then decreased in the last section. This pattern of the variation was similar in the glacial and modern samples. The delta-13C value within an annual ring seems to be controlled by environmental factors (not plant physiological ones), since there was no isotopic shift in the seasonal delta-13C variation at the earlywood-latewood boundary, which was controlled by plant physiology. The result suggests the potential to reconstruct the paleoenvironment within a year using the seasonal delta-13C variation, though site-specific conditions such as soil characteristics would also affect to its fluctuation.