• Factorial Design Techniques Applied to Optimization of AMS Graphite Target Preparation

      Verkouteren, R. M.; Klouda, G. A. (Department of Geosciences, The University of Arizona, 1992-01-01)
      Many factors influence the preparation and quality of graphite targets for 14C accelerator mass spectrometry (AMS). We identified four factors (sample size, HZ pressure, catalyst temperature and pretreatment time) as potentially critical, and investigated their effects on two particular characteristics; the integrated rates of CO2 reduction (to graphite) and methane production. We used a 2-level fractional factorial experimental design and determined chemical reduction yield rates through manometry and partial pressure monitoring of residual gases by mass spectrometry. Chemical reduction yield rates ranged from 0.2% to 6.2% per hour. With respect to their influence on percent yield rate, the factors we studied were ordered as; sample size > level of hydrogen > pretreatment of the catalyst. The temperature of the catalyst, and the sample size x hydrogen (2-factor) interaction, were only marginally influential. Other interactions did not appear to be significantly important. We estimated uncertainty in the order of influence and magnitudes of the effects by the Monte Carlo method of error propagation. We observed significant methane production in only one experiment, which suggests that methane originates from indigenous carbon in untreated iron catalyst only in the presence of hydrogen and only at thermodynamically favorable temperatures. This exploratory investigation indicates that factorial design techniques are a useful means to investigate multivariate effects on the preparation and quality of AMS graphite targets.
    • Factors Influencing 14C Ages of the Pacific Rat Rattus exulans

      Ragano Beavan, Nancy; Sparks, Rodger J. (Department of Geosciences, The University of Arizona, 1998-01-01)
      An isotopic database for the Pacific/Polynesian rat (Rattus exulans) and foods that it scavenges is used to examine diet-induced 14C age variation in omnivores. We discuss a suite of 26 Delta-14C determinations and 13C and 15N analysis for modern Pacific/Polynesian rat bone gelatin and available food items from Kapiti Island, New Zealand (40 degrees 51'S, 174 degrees 75'E). These analyses provide the first isotopic data for modern specimens of the species, collected as part of a larger project to determine potential sources of bias in unexpectedly old 14C age measurements on subfossil specimens of R. Exulans from New Zealand. Stable C, N and 14C isotopic and trapping data are used to trace carbon intake via the diet of the rats in each habitat. Data from specimens linked to five specific habitats on the island indicate that modern populations of R. Exulans are not in equilibrium with atmospheric values of Delta-14C, being either enriched or depleted relative to the atmospheric curve in 1996/97, the period of collection. The Delta-14C values recorded for R. Exulans are associated with diet, and result from variation in Delta-14C values found in animal-protein food items available to a scavenging omnivore. The titer of carbon deviating from atmospheric values is believed to be derived from the essential amino acids in the protein-rich foods of the rat diet. Present evidence suggests that the depletion required to affect 14C ages limits the possibility that diet introduces dramatic offsets from true ages. Marine diets, for example, would have a variable effect on ages for terrestrial omnivores, contraindicating the application of a standard marine correction for such specimens. We suggest that to identify the extent to which diet may influence the 14C age in a given specimen of terrestrial omnivore, the separation and dating of essential amino acids vs. A nonessential amino, such as glycine, be applied.
    • Fast 14C Sample Preparation of Organic Material

      Dörr, Helmut; Kromer, Bernd; Münnich, Karl Otto (Department of Geosciences, The University of Arizona, 1989-01-01)
      A fast 14C sample preparation technique for organic material in conventional 14C counting is described. The basic difference from conventional preparation is oxidation of the organic substances in a closed system under an oxygen pressure of ca 10 bars. After the explosion-like combustion, the reaction products SO2 and NO2 are oxidized immediately to SO4^-2 and NO3^- and precipitated on the wall of the reaction vessel. The residual gis mixture is passed first through a cold trap at -78 degrees C to remove water vapor and then through an activated charcoal column at 0 degrees C for purification. CO2 is removed from the remaining O2-CO2 gas mixture in a LN2 trap at a pressure approximately equal to 100mbar. With this method sample preparation time is reduced from ca 10 hr to ca 1 hr. The efficiency and reproducibility of the procedure is shown with 14C and 13C measurements of a sugar-carbon standard. The results obtained by the new technique agree well with conventionally prepared wood and bone samples.
    • Fast and Accurate Sequential Injection AMS with Gated Faraday Cup Current Measurement

      Klein, M.; Mous, D. J. W.; Gottdang, A. (Department of Geosciences, The University of Arizona, 2004-01-01)
      Sequential injection or bouncing has a number of properties which can lead to a reduction of the analysis accuracy if no appropriate measures are taken. A special injection system has been developed in order to eliminate these shortcomings. The influence of source glitches or instabilities on the measured isotopic ratio is substantially reduced by a high cycling frequency. A fast beam-blanking unit guarantees the needed accuracy of the injection periods. Background currents are avoided by synchronizing the current measurement for the stable isotopes with their injection periods. To achieve the required speed and precision of the gated measurement, new instrumentation was developed. The elimination of background contributions allows an efficiency for radiocarbon counting as high as 95% at a cycling frequency of 100 Hz.
    • Fast and Complete CO2-to-Graphite Conversion for 14C Accelerator Mass Spectrometry

      Hut, Gert; Östlund, H. Göte; van der Borg, Klaas (American Journal of Science, 1986-01-01)
      With Fe powder as a catalyst, CO2 is completely converted to graphite within 90 minutes. The reaction proceeds at 650 degrees C with an excess of H2. The reaction rate is enlarged by forced circulation and by keeping the water vapor pressure very low. The graphite samples obtained, consisting of 5mg of carbon, almost immediately produce stable 12C- currents of the order of 20-30 micro-A in the sputter source of a Van de Graaff accelerator. The currents can be maintained for at least 10 hours and are comparable to those from commercial graphite. No memory effects in the preparation system have been observed.
    • Fine and Hyperfine Structure in the Spectrum of Secular Variations of Atmospheric 14C

      Damon, Paul E.; Cheng, Songlin; Linick, Timothy W. (Department of Geosciences, The University of Arizona, 1989-01-01)
      The coarse structure of the 14C spectrum consists of a secular trend curve that may be closely fit by a sinusoidal curve with period ca 11,000 yr and half amplitude +/- 51 per mil. This long-term trend is the result of changes in the earth's geomagnetic dipole moment. Consequently, it modulates solar components of the 14C spectrum but does not appear to modulate a component of the spectrum of ca 2300-yr period. The ca 2300-yr period is of uncertain origin but may be due to changes in climate because it also appears in the delta-18O spectrum of ice cores. This component strongly modulates the well-known ca 200-yr period of the spectrum's fine structure. The hyperfine structure consists of two components that fluctuate with the 11-yr solar cycle. One component results from solar-wind modulation of the galactic cosmic rays and has a half-amplitude of ca +/- 1.5%. The other component is the result of 14C production by solar cosmic rays that arrive more randomly but rise and fall with the 11-yr cycle and appear to dominate the fluctuation of the galactic cosmic-ray-produced component by a factor of two.
    • Fire History of a Giant African Baobab Evinced by Radiocarbon Dating

      Patrut, A.; Mayne, D. H.; Von Reden, Karl F.; Lowy, Daniel A.; van Pelt, Robert; McNichol, Ann P.; Roberts, Mark L.; Margineanu, D. (Department of Geosciences, The University of Arizona, 2010-01-01)
      The article reports the first radiocarbon dating of a live African baobab (Adansonia digitata L.), by investigating wood samples collected from 2 inner cavities of the very large 2-stemmed Platland tree of South Africa. Some 16 segments extracted from determined positions of the samples, which correspond to a depth of up to 15-20 cm in the wood, were processed and analyzed by accelerator mass spectrometry (AMS). Calibrated ages of segments are not correlated with their positions in the stems of the tree. Dating results indicate that the segments originate from new growth layers, with a thickness of several centimeters, which cover the original old wood. Four new growth layers were dated before the reference year AD 1950 and 2 layers were dated post-AD 1950, in the post-bomb period. Formation of these layers was triggered by major damage inside the cavities. Fire episodes are the only possible explanation for such successive major wounds over large areas or over the entire area of the inner cavities of the Platland tree, able to trigger regrowth.
    • First 14C Results from Archaeological and Forensic Studies at the Vienna Environmental Research Accelerator

      Wild, Eva; Golser, Robin; Hille, Peter; Kutschera, Walter; Priller, Alfred; Puchegger, Stephan; Rom, Werner; Steier, Peter; Vycudilik, W. (Department of Geosciences, The University of Arizona, 1998-01-01)
      14C dating with the new Vienna Environmental Research Accelerator (VERA) began with the age determination of a mummified marmot found in the Austrian Alpine region. Soft tissue and bones of the marmot were used for the investigation. For comparison, bone material from known-age samples was also processed and measured. These exercises showed that 14C dating with VERA is reliable, and since that time various samples from archaeological context have been dated. We also studied the applicability of the 14C method in forensic sciences to determine the time of death of human individuals. 14C/ 12C measurements of samples from different organic human material (bone collagen, lipids from bone and bone marrow, hair) were performed and compared with the tropospheric "bomb peak" values to transform the measured ratios into "calibrated ages". For specific substances with rapid turnover rates, this gives an estimate for the time of death of the individual. In our study, lipids and hair yield reasonable times of death, whereas the collagen fraction from bones, which has a relatively long turnover time, is not suitable for this purpose.
    • First Direct AMS Dates on Early Maize from Tehuacán, Mexico

      Long, Austin; Benz, B. F.; Donahue, D. J.; Jull, A. J. T.; Toolin, L. J. (Department of Geosciences, The University of Arizona, 1989-01-01)
      The Tehuacán region in Central Mexico is thought to be the locale of origin of Zea mays, or maize, a cultivated plant pivotal in the development of agriculture in the Americas (MacNeish, 1981, 1985). The age of the earliest maize, and its rate of dispersal are thus important components of cultural development in the New World. We have secured permission from the Federal Government of Mexico to date critical specimens from Tehuacan, which represent what are probably some of the earliest known stages of maize evolution. Twelve Zea mays samples have been dated, six from Cueva San Marcos and six from Cueva Coxcatlán. These were selected as having the best stratigraphic control and correlation with previously dated charcoal samples, and to represent the most ancient maize. Corn from Cueva San Marcos is oldest: four of the six specimens from this cave were within statistics of 4700 BP (uncalibrated). The oldest known domesticated corn is thus no older than 3600 cal BC (dendro-calibrated in calendric years).
    • First Lapita Settlement and its Chronology in Vava'u, Kingdom of Tonga

      Burley, David V.; Connaughton, Sean P. (Department of Geosciences, The University of Arizona, 2007-01-01)
      Beginning approximately cal 1400 BC, Austronesian-speaking Lapita peoples began a colonizing migration across Oceania from the Bismarck Archipelago to western Polynesia. The first point of entry into Polynesia occurred on the island of Tongatapu in Tonga with subsequent spread northward to Samoa along a natural sailing corridor. Radiocarbon measurements from recent excavations at 4 sites in the northern Vavau islands of Tonga provide a chronology for the final stage of this diaspora. These dates indicate that the northern expansion was almost immediate, that a paucity of Lapita sites to the north cannot be explained as a result of lag time in the settlement process, and that decorated Lapita ceramics disappeared rapidly after first landfalls.
    • First Reported Samples from the Radiocarbon Laboratory of the University of Tennessee Center for Archaeometry and Geochronology: Dates from the McCrosky Island Archaeological Site (40SV43), Sevier County, Tennessee, USA

      Weinand, Daniel C.; Polhemus, Richard R.; Blankenship, Sarah A.; Simek, Jan F. (Department of Geosciences, The University of Arizona, 2008-01-01)
      This study presents the results of archaeological samples submitted for dating at the recently constructed University of Tennessee Center for Archaeometry and Geochronology (UTCAG) radiocarbon dating laboratory (Knoxville, Tennessee, USA). The samples selected for this initial study were obtained from excavations at the McCrosky Island site (40SV43) in Sevier County, Tennessee, USA. Three of the samples dated were split between the UTCAG laboratory and another laboratory to assess the UTCAG laboratory protocols. In an effort to further validate the laboratory methods employed, several other samples were submitted without prior knowledge of contextual data. The dates obtained for these samples were then compared to their association with recovered artifacts and/or archaeological context.
    • First Results from the Groningen AMS Facility

      van der Plicht, Johannes; Aerts, Anita; Wijma, Stef; Zondervan, Albert (Department of Geosciences, The University of Arizona, 1995-01-01)
      A new generation accelerator mass spectrometer has been installed at the Centre for Isotope Research in Groningen, The Netherlands. It is a dedicated 14C machine, with a capacity of measuring 3000 samples per year with high precision (<0.5%). The system has been in full operation since the summer of 1994. We present here a short summary of the results and performance obtained thus far.
    • Fish Reservoir Effect on Charred Food Residue 14C Dates: Are Stable Isotope Analyses the Solution?

      Boudin, M.; Van Strydonck, M.; Crombé, P.; De Clercq, W.; van Dierendonck, R. M.; Jongepier, H.; Ervynck, A.; Lentacker, A. (Department of Geosciences, The University of Arizona, 2010-01-01)
      In order to verify the relative dating based on pot type morphology and decoration of the Swifterbant pottery collected at the Final Mesolithic site of Doel "Deurganckdok" (Belgium) and of the Late Iron Age pottery excavated at Grijpskerke (the Netherlands), direct radiocarbon dates were obtained on charred food residue preserved on the inner surface of numerous potsherds. In addition, a number of indirect 14C dates were obtained from samples of organic material. In the case of Doel, the results indicate an important incompatibility between the charred food residue dates and the other dates, the former being systematically older. This difference may be explained by a reservoir effect of the charred food residue, caused by the processing of (freshwater) fish. The 14C dates for the rijpskerke site are in agreement between the charred food residue and the organic material. The stable isotopes of the charred food residue were analyzed to demonstrate fish processing in the pottery, but the results were inconclusive.
    • Floating Larch Tree-Ring Chronologies from Archaeological Timbers in the Russian Altai Between About 800 BC and AD 800

      Panyushkina, Irina; Sljusarenko, Igor; Bikov, Nikolay; Bogdanov, Eugene (Department of Geosciences, The University of Arizona, 2007-01-01)
      We obtained over 200 archaeological wood specimens from the southeastern part of the Altai Mountains (Russia) to establish accurate calendar dates of the timbers using both radiocarbon and tree-ring analyses. Most timbers came from small and elite tombs of the Pazyryk culture (Siberian Scythians of the Iron Age period). Timbers from Hun-Sarmatian and Turk times (1st millennium AD) were studied for the first time. Three floating tree-ring width chronologies of larch (Larix sibirica) with lengths of 486 yr to 144 yr were developed from the tree-ring data. Tree rings of the composite 486-yr chronology of the Pazyryk culture represent the regional scale of Altai tree-ring width variability between about 720-240 BC. The composite chronology dates the earliest construction of Pazyryk culture tombs to ~320 BC (ordinary tombs) and the latest ones at 240 BC (Pazyryk noble tomb #5). The composite chronology might be used for tree-ring dating wood from Scythian tombs in the region. It will also help confirm the precision of 14C dating of the Scythian tombs around the Hallstatt plateau of 14C calibration curves. We developed a 110-yr decadal 14C sequence from the Kurayka site that dates Kok-Pash culture timbers back to cal AD 240 (Hun-Sarmatian period). 14C dates of wooden poles from 3 sites of Turk stone enclosures suggested wood cutting dates between cal AD 470 and 830. The results demonstrate that crossdating tree rings along with 14C dating of crossdated rings provide the most reliable and highest precision dates for these archaeological sites.
    • Florence Radiocarbon Dates I

      Azzi, C. M.; Bigliocca, L.; Piovan, E. (American Journal of Science, 1973-01-01)
    • Florence Radiocarbon Dates II

      Azzi, C. M.; Bigliocca, L.; Piovan, E. (American Journal of Science, 1974-01-01)
    • Florence Radiocarbon Dates III

      Azzi, C. M.; Bigliocca, L.; Gulisana, F. (American Journal of Science, 1977-01-01)
    • Florence Radiocarbon Dates IV

      Azzi, C. M.; Gulisano, F. (American Journal of Science, 1979-01-01)
    • Florida State University Radiocarbon Dates I

      Stipp, J. J.; Knauer, G. A.; Goodell, H. G. (American Journal of Science, 1966-01-01)