• 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.
    • 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.
    • 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.
    • Temporal 10Be Variations in Ice

      Beer, Jürg; Andree, Michael; Oeschger, Hans; Stauffer, Bernhard; Balzer, Richard; Bonani, Georges; Stoller, Christian; Suter, Martin; Wölfli, Willy; Finkel, Robert C. (American Journal of Science, 1983-01-01)
    • The Integration of Radiocarbon Dating in Archaeology

      Waterbolk, H. T. (American Journal of Science, 1983-01-01)
    • The Oxford Radiocarbon Accelerator Facility

      Gillespie, Richard; Hedges, R. E. M.; White, N. R. (American Journal of Science, 1983-01-01)
    • The Radon Problem in 14C Dating

      Nydal, Reidar (American Journal of Science, 1983-01-01)
      Due to traces of radium and uranium in most 14C samples, radon appears as a radioactive contamination in the CO2 prepared by combustion. This contamination must be removed by an active purification prodecure or by storing the CO2 prior to measurement. No effective electronic discrimination against radon and its daughter elements can be performed. The necessary storage time until radon has decayed varies widely, especially for marine shells. The latter material, collected from Norway and Svalbard, has been a main object for the present investigation. In a few cases, a measureable amount of radon may be left even after eight weeks. The behavior of radon and its daughter elements in a CO2 proportional counter has been studied.
    • The Reliability of Archaeologic Interpretation of Radiocarbon Dates

      Willkomm, Horst (American Journal of Science, 1983-01-01)
      14C dates of a medieval settlement with archaeologically well-dated strata are compared with the true ages of the respective layers. The 14C values indicate that each layer may contain older material reaching up to the beginning of settlement. Therefore, the 14C measurement of only a few wood or charcoal samples may lead to age estimations several hundred years too old.
    • The Unreliability of 14C Dates Obtained from Buried Sandy Podzols

      Geyh, Mebus A.; Roeschmann, Günter; Wijmstra, T. A.; Middeldorp, A. A. (American Journal of Science, 1983-01-01)
      A test for the reliability of 14C dating of soil was made at two sites with buried, autochthonous, and in parts, allochthonous sandy podzols, dated either lithoand pedostratigraphically or palynologically. The differences between the age ranges obtained and the apparent mean residence times (AMRT) calculated from the 14C content of alkaline extracts from fossil soil layers and horizons lean in organic matter exceed 10,000 years, corresponding to a maximum contamination with recent carbon of up to 50 %. The use of correction factors for the apparent mean residence times of podzols is not valid, not even for climate zones, because these values have a broad scatter for the same profile.
    • The Use of 14C in Natural Materials to Establish the Average Gaseous Dispersion Patterns of Releases from Nuclear Installations

      Otlet, M. L.; Walker, A. J.; Longley, H. (American Journal of Science, 1983-01-01)
      The Harwell Low Level measurements been measuring a variety of natural materials close to United Kingdom nuclear installations measurements are made first, to establish the releases to the atmosphere of 14C as observed tree rings and second, to establish dispersion contours ed over extended periods. The main study area has been Cumbria, around the BNFL nuclear installation at Sellafield. 14C, which can be measured to good precision even at values close to the normal natural levels, provides a powerful technique for the provision of practical experimental values much wanted for theoretical dispersion models.
    • Time History of Human Gallstones: Application of the Post-Bomb Radiocarbon Signal

      Druffel, Ellen M.; Mok, Henry Y. I. (American Journal of Science, 1983-01-01)
      Bomb-produced 14C is a valuable tool for studying rates of short-term processes involving carbon cycling. This study shows that bomb 14C is an excellent tracer of a biochemical process that takes place in the human body, namely the accretion of stones in the gallbladder. The methods developed for obtaining time histories of 14C/12C and 13C/12C in concentric layers from a large gallstone (30mm diameter) are reported. Formation times are assigned by matching the 14C/12C obtained from individual layers with those found for known-aged tree rings. Results show that the gallstone grew over a period of 10 years and seems to have lain dormant within the gallbladder for a period of 11 years. The average growth rate was 1.5mm/year.