• Using the Bayesian Method to Study the Precision of Dating by Wiggle-Matching

      Goslar, Tomasz; Mądry, Wiesław (Department of Geosciences, The University of Arizona, 1998-01-01)
      The "wiggle-matching" technique has been widely used for the absolute dating of a series of radiocarbon-dated samples connected in one floating chronology. This is done by calculations of SS statistics (the mean-square distance of 14C ages of samples from the calibration curve) calculated for any assumed calendar age of the floating chronology. In the standard procedure the confidence intervals of true calendar age are derived from the width of the SS minimum, using the critical values of the chi-square distribution. This, however, seems oversimplified. Another approach is an extension of the Bayesian algorithm for calibration of single 14C dates. Here, we describe in detail the Bayesian procedure and discuss its advantages compared to the SS minimization method. Our calculations show that for given errors of 14C measurements, precision of dating the series is related to the shape of the SS curve around its minimum, rather than to the absolute value of SSmin. In some cases, dating precision may be improved more efficiently by extending the time span covered by the series rather than by improving the precision of the 14C measurements. The application of the Bayesian method enabled us to delimit the age of the floating varve chronology from the sediments of Lake Gościąż with distinctly better accuracy than was previously reported using the SS curve alone.
    • Calibration of the 14C Time Scale Beyond 22,000 BP

      Geyh, Mebus A.; Schlüchter, Christian (Department of Geosciences, The University of Arizona, 1998-01-01)
      The conventional 14C time scale between 11,500 and 22,000 sidereal years has been calibrated by TIMS U/Th dates for corals. Only a few studies have been made for the time beyond this range. Obtaining samples suitable for numerical dating or estimating the reservoir correction of the 14C dates has been difficult, but we do not have these problems with TIMS U/Th dating of interstadial and interglacial lignite, because reservoir corrections are unnecessary.
    • Calibration Technique for 14C Data Clusters: Fitting Relative Chronologies onto Absolute Time Scales

      Haas, Herbert; Doubrava, Matthew R. (Department of Geosciences, The University of Arizona, 1998-01-01)
      Application of radiocarbon dating to a short chronology is often limited by the wide probability ranges of calibrated dates. These wide ranges are caused by multiple intersections of the 14C age with the tree-ring curve. For a single unrelated 14C date, each intersection presents a probable solution. When several dates on different events are available, identification of the most probable solution for each event is possible if one can obtain some information on the relation between these events. We present here a method for such identifications. To demonstrate the method, we selected a series of 14C dates from mortuary monuments of the Egyptian Old Kingdom. Corrected 14C dates from seven monuments were used. Calibration of these dates produced three absolute ages with single intersections and four ages with 3-5 intersections. These data are compared to a historical chronology, which places the dated events at a younger age. If each intersection is chosen as a potential anchor point of the "correct" chronology, 17 solutions must be tested for the best fit against the historical chronology. The latter is based on the length of the reign of each pharaoh during the studied time span. The spreadsheet has the function of determining the probability of fit for each of the solutions. In a second step the 17 probability values and their offset between the historical and the 14C chronology are graphically analyzed to find the most probable offset. This offset is then applied as a correction to the estimated chronology to obtain an absolute time scale for the dated events.
    • Changes of the CO2 Sources and Sinks in a Polluted Urban Area (Southern Poland) Over the Last Decade, Derived from the Carbon Isotope Composition

      Kuc, Tadeusz; Zimnoch, Mirosław (Department of Geosciences, The University of Arizona, 1998-01-01)
      Time series of Delta-14C, delta-13C, and concentration of atmospheric CO2 covering the last 12 years are available at the Krakow sampling site (southern Poland) representing an urban area exposed to anthropogenic pollution of both local and regional origin. The samples represent continuous monitoring in biweekly intervals. Observations covering the time period 1983-1994 show a linear decrease of the 13C/12C ratio (delta-13C = -9.6 per mil in Jan. 1983) with a slope of -0.02 per mil a-1. The decreasing tendency in the case of 14C (Delta-14C = 227 per mil in January 1983) is weaker with a broad minimum in 1991 (Delta-14C = 124 per mil) and subsequent gradual increase by ca. 10 per mil, coinciding with a substantial reduction of coal consumption in Poland (26% reduction in 1991-1994 for heat and electricity production), partly compensated in agglomerations by increased gas consumption. The 12-year record of the CO2 concentration in Krakow points to a constant value fluctuating at a high level (average: 373 ppmv) reaching a maximum yearly average of 376 ppmv. These carbon isotope signatures were used for the separation of fossils from biogenic and "background" components, reflecting the strength of relevant sources. The monthly mean of the fossil component varies from ca. 10 ppmv in June to 27.5 ppmv in March while the yearly mean decreased ca. 16 ppmv since 1991.
    • Interlaboratory Comparisons: Lessons Learned

      Scott, E. M.; Harkness, D. D.; Cook, G. T. (Department of Geosciences, The University of Arizona, 1998-01-01)
      Interlaboratory comparisons have been widely used in analytical chemistry and radiochemistry as an important part of ongoing quality assurance programs. The 14C community has been no exception in this respect, and in just under 20 years, there have been a number of significant and very extensive interlaboratory trials organized by individual laboratories and the International Atomic Energy Agency (IAEA) to the benefit of the 14C community (both labs and users) (Otlet et al. 1980; ISG 1982; Scott et al. 1990; Rozanski et al. 1992; Scott et al. 1992; Gulliksen and Scott 1995). The comparisons have varied widely in terms of sample type and preparation, but all have had as their primary goal the investigation of the comparability of results produced under possibly quite different laboratory protocols. As techniques have been developed and new labs formed, the reference materials created as a result of the intercomparisons have presented an opportunity for checking procedures and results. Users have been reassured by the existence of regular comparisons as one sign of the concern that laboratories have to ensure highest quality results, but also confused about how to make use of the results from past exercises in the interpretation of sets of dates from many laboratories. The laboratories have also learned valuable lessons from participation in such studies. These have included identification of systematic offsets and additional sources of variation and in studies which have used realistic samples requiring pretreatment, chemical synthesis and counting, it has been possible to identify the stage at which such problems have arisen and to quantify the relative contributions to the overall variation. In this paper, we will briefly review the comparisons so far, draw some conclusions from their findings, and make proposals for the future organization of intercomparisons.
    • 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.
    • A 40,000-Year Varve Chronology from Lake Suigetsu, Japan: Extension of the 14C Calibration Curve

      Kitagawa, Hiroyuki; van der Plicht, Johannes (Department of Geosciences, The University of Arizona, 1998-01-01)
      A sequence of annually laminated sediments is a potential tool for calibrating the radiocarbon time scale beyond the range of the absolute tree-ring calibration (11 ka). We performed accelerator mass spectrometric (AMS) 14C measurements on >250 terrestrial macrofossil samples from a 40,000-yr varve sequence from Lake Suigetsu, Japan. The results yield the first calibration curve for the total range of the 14C dating method.
    • Reproducibility of Seawater, Inorganic and Organic Carbon 14C Results at NOSAMS

      Elder, Kathryn L.; McNichol, Ann P.; Gagnon, Alan R. (Department of Geosciences, The University of Arizona, 1998-01-01)
      The majority of samples processed at the National Ocean Sciences AMS Facility (NOSAMS) thus far were collected as part of the World Ocean Circulation Experiment (WOCE). Due to the long storage time (2-3 yr) required to analyze thousands of samples on the accelerator mass spectrometer (AMS), a test was designed and implemented to determine the effects, if any, of storage time on 14C concentration. We find no systematic offsets in AMS measurements made over a 5-yr period between a total of 16 replicate sets from surface and deep water collected at the same locality. Furthermore, the average Delta-14C value from the deepwater AMS replicates (-213.1 per mil, std. dev. 7.3) agrees very closely with the conventional 14C results published for GEOSECS (-212.7 per mil) from station 320 taken 20 yr earlier. A total of 73 WOCE shipboard replicate sets (162 AMS measurements) were analyzed with a mean precision of 4.3 per mil. AMS results from 20 more shipboard replicate sets (44 AMS measurements) submitted as CO2 from the Stable Isotope Laboratory (SIL) at the University of Washington were analyzed with a mean precision of 3.4 per mil. These results suggests no significant difference between water stripping methods used in each preparation lab. To assess reproducibility, we calculate a pooled estimate of sigma for replicates called s, which we use as an approximation of sigma (sub TOT) for a given sample type. The s for WOCE seawater replicates is 4.9 per mil and 5.8 per mil for SIL gas replicates. These numbers demonstrate an overall reproducibility of seawater AMS results at NOSAMS that is in line with reported errors. We take the difference between total error s and machine error as the overall standard deviation of combined uncertainties associated with preparation of samples and with AMS. For seawater samples processed at NOSAMS, sigma (sub SPL) is calculated to be 2.4 per mil, and for the SIL gas replicates it is 4.8 per mil. Reproducibility of samples prepared with an acid hydrolysis technique is demonstrated using 24 coral samples submitted in triplicate by Dr. R. G. Fairbanks of Lamont Doherty Earth Observatory. Seventy-two replicates were prepared and analyzed at NOSAMS with a mean reported precision of 1.2 per mil. The pooled estimate s for the Fairbanks triplicates is 2.6 per mil. We calculate a laboratory reproducibility uncertainty for coral hydrolysis samples of 2.2 per mil. In 1993, NOSAMS participated in the Third International Radiocarbon Intercomparison (TIRI) Study. We report here 60 AMS analyses of the six TIRI test materials, five of which are organic carbon samples, to validate sample-processing methods for organic carbon sample AMS analyses at NOSAMS.
    • Secular Variation of Delta-14C During the Medieval Solar Maximum: A Progress Report

      Damon, P. E.; Eastoe, C. J.; Hughes, M. K.; Kalin, R. M.; Long, A.; Peristykh, A. N. (Department of Geosciences, The University of Arizona, 1998-01-01)
      The Earth is within the Contemporaneous Solar Maximum (CSM), analogous to the Medieval Solar Maximum (MSM). If this analogy is valid, solar activity will continue to increase well into the 21st century. We have completed 75 single-ring and 10 double-ring measurements from AD 1065 to AD 1150 to obtain information about solar activity during this postulated analog to solar activity during the MSM. Delta-14C decreases steadily during the period AD 1065 to AD 1150 but with cyclical oscillations around the decreasing trend. These oscillations can be successfully modeled by four cycles. These four frequencies are 1/52 yr-1, 1/22 yr-1, 1/11 yr-1, and 1/5.5 yr, i.e., the 4th harmonic of the Suess cycle, the Hale and Schwabe cycles and the 2nd harmonic of the Schwabe cycle.
    • A Remotely Operated, Field-Deployable Tritium Analysis System for Surface and Ground Water Measurement

      Noakes, J. E.; Spaulding, J. D.; Neary, M. P. (Department of Geosciences, The University of Arizona, 1998-01-01)
      We have worked in collaboration with the Westinghouse Savannah River Company and Packard Instrument Company to develop a prototype instrument for remote, near real-time, in situ analysis of environmental levels of tritium in surface and ground water samples. The unit consists of a Packard Radiomatic(TM) 525TR liquid scintillation counter that has been modified to achieve lower detection levels through background reduction using Packard's After-Pulse Burst Discrimination electronics and an auxiliary Bi4Ge3O12 scintillation detector guard. The system is fully programmable to enable remote calibration, sample collection, sample analysis, reconfiguration of operational mode and interrogation for analytical results.
    • An Attempt at Absolute 14C Dating

      Szabo, Jacob; Carmi, Israel; Segal, Dror; Mintz, Eugenia (Department of Geosciences, The University of Arizona, 1998-01-01)
      The accepted state-of-the-art 14C dating method relies on calibration curves to determine initial 14C levels in a sample. The paper reconsiders the basis of 14C dating and offers a possible alternative that eliminates the need to employ calibration curves. The idea is to measure the level of radiogenic nitrogen atoms retained in the sample molecules after 14C beta-decay. The practicality of this alternative method still has to be proven.
    • An Experiment to Refute the Likelihood of Cellulose Carboxylation

      Hedges, R. E. M.; Bronk Ramsey, Christopher; Van Klinken, G. J. (Department of Geosciences, The University of Arizona, 1998-01-01)
      To test the hypothesis that cellulose in linen can be carboxylated at high temperatures in the presence of CO2, water and silver, we heated two aliquots of cellulose extracted from old wood in glass ampoules, adding Ag powder to one to test its potential action as a catalyst for the carboxylation reaction. AMS measurement of the heated aliquots showed no statistically significant difference in 14C content from the "uncarboxylated" cellulose. We conclude that carboxylation is not a systematic source of error in the dating of cellulose-containing materials such as the linen in the Shroud of Turin.
    • An Ion Source for the HVEE 14C Isotope Ratio Mass Spectrometer for Biomedical Applications

      Mous, Dirk W.; Fokker, Wim; Van Den Broek, Rein; Koopmans, Ron; Bronk Ramsey, Christopher; Hedges, R. E. M. (Department of Geosciences, The University of Arizona, 1998-01-01)
      During the past two decades, accelerator mass spectrometry (AMS) has allowed major developments in many areas of geosciences and archaeology. In the near future, AMS should realize a similar potential in the field of biomedical research, leading ultimately to clinical applications. For such applications, the required instrument differs significantly from that presently used in the field of 14C dating. Whereas the needed accuracy and sensitivity is more than an order of magnitude less demanding than that for present state-of-the-art 14C instrumentation, the widespread acceptance of 14C AMS in biomedical research will require AMS spectrometers that are small, simple to operate and capable of handling CO2 samples. In order to satisfy these demands, HVEE has developed a compact 14C AMS spectrometer dedicated to biomedical research. The instrument consists of a compact accelerator with a footprint of 2.25 x 1.25 m and an ion source that features direct CO2 acceptance and optimal user friendliness. Having previously described the layout and design of the accelerator, we here discuss progress on the accelerator and present the design and first results of the CO2 ion source.
    • Attempt to Affect the Apparent 14C Age of Cotton by Scorching in a CO2 Environment

      Long, Austin (Department of Geosciences, The University of Arizona, 1998-01-01)
      One explanation for the radiocarbon dates on the Shroud of Turin being younger than the time of Christ is that the heat from a fire, which scorched a portion of the Shroud, may have affected the 14C content (dates) on the shroud by affecting molecular exchange between the fabric and atmospheric carbon. This report describes a laboratory test on the susceptibility of cellulose, in the form of cotton, to incorporate carbon from CO2 while it is heated in a closed tube with carbon dioxide until the cotton considerably darkened. To maximize the effect of this hypothetical process, we simulated the shroud material with cotton that had a 14C level of 0.55 modern (55 pMC, equivalent to 4800 yr), and the atmosphere with pure CO2, which had a 14C level of 1.3 modern (130 pMC). No measurable 14C transferred from the gas phase to the solid phase. The implication of this test is that scorching is an unlikely mechanism to affect the apparent age of cellulose-like material.
    • 14C Analysis of Annual Tree Rings from the Vicinity of the Chernobyl NPP

      Buzinny, Michael; Likhtarev, Ilja; Los', Ivan; Talerko, Nikolay; Tsigankov, Nikolay (Department of Geosciences, The University of Arizona, 1998-01-01)
      Samples of >40 pine trees were collected from around the Chernobyl NPP for radiocarbon measurement, to determine the spatial distribution of excessive 14C in tree rings from 1986 consequent upon accidental radiocarbon release. Tree samples were collected during 1995-1996 from sites situated at distances >2.5 km from the NPP and covering a variety of directions in relation to the NPP. To evaluate Delta-14C for 1986 annual rings, we compared 14C levels for separate 1985-1987 annual rings, taking into account the trend of operational releases. Early and late wood samples for 1986 annual tree rings were measured separately to increase the sensitivity and precision of measurements. The maximum value observed for excessive accidental radiocarbon levels (Delta-14C) was found to be 124 pMC (281.6 Bq kg-1 C). We present Delta-14C values for examined sites; their spatial distribution shows a high irregularity of atmospheric 14C depending on direction from the NPP. Using obtained data, we reconstruct the temporal behavior of 14C release during the Chernobyl accident with the aid of atmospheric transport modeling. The total amount of 14C released from 26 April to 5 May 1986 has been estimated as 44 TBq.
    • 14C AMS Measurements of <100 Microgram Samples with a High-Current System

      von Reden, K. F.; McNichol, Ann P.; Pearson, Ann; Schneider, Robert J. (Department of Geosciences, The University of Arizona, 1998-01-01)
      The NOSAMS facility at Woods Hole Oceanographic Institution has started to develop and apply techniques for measuring very small samples on a standard Tandetron accelerator mass spectrometry (AMS) system with high-current hemispherical Cs sputter ion sources. Over the past year, results on samples ranging from 7 to 160 micrograms C showed both the feasibility of such analyses and the present limitations on reducing the size of solid carbon samples. One of the main factors affecting the AMS results is the dependence of a number of the beam optics parameters on the extracted ion beam current. The extracted currents range from 0.5 to 10 micro-A of 12Cfor the sample sizes given above. We here discuss the setup of the AMS system and methods for reliable small-sample measurements and give the AMS-related limits to sample size and the measurement uncertainties.
    • Groningen, a Few Months After...

      van der Plicht, Hans (Department of Geosciences, The University of Arizona, 1998-01-01)
    • 14C Levels in the Vicinity of Two Swedish Nuclear Power Plants and at Two "Clean-Air" Sites in Southernmost Sweden

      Stenström, Kristina; Skog, Göran; Thornberg, Charlotte; Erlandsson, Bengt; Hellborg, Ragnar; Mattsson, Sören; Persson, Per (Department of Geosciences, The University of Arizona, 1998-01-01)
      14C is one of the radionuclides that are produced to different degrees by neutron-induced reactions in all types of nuclear reactors. Part of the 14C created is continuously released into the surrounding environment during normal operation as airborne effluents in various chemical forms (such as CO2, Co and hydrocarbons) through the ventilation system of the plant. Because of the biological importance of carbon and the long half-life of 14C, it is of interest to measure the releases and their incorporation into living material. We report here on the 14C activity concentrations in annual tree rings and the air around two Swedish nuclear power plants, as well as the background 14C activity levels from two reference sites in southern Sweden from 1973-1996. We used both accelerator mass spectrometry (AMS) and decay counting in the investigation.
    • A Tree-Ring and 14C Chronology of the Key Sayan-Altai Monuments

      Zaitseva, G. I.; Vasiliev, S. S.; Marsadolov, L. S.; van der Plicht, J.; Sementsov, Anatoly A.; Dergachev, Valentin A.; Lebedeva, L. M. (Department of Geosciences, The University of Arizona, 1998-01-01)
      We present a radiocarbon chronology of key Sayan-Altai monuments from the Scythian period, based on a statistical analysis of dates produced in the 1980s and now supplemented with new dates. These new 14C dates were produced for samples from the Tuekta-1 barrows (burial mounds) and were measured both in St. Petersburg and Groningen. These tree-ring samples were fitted to the calibration curve. Chronologies were established for the Arzhan, Tuekta-1 and Pazyryk-5 barrows. The time of the construction of the Arzhan and Pazyryk-5 barrows is the 9th and late 5th-4th centuries BC, respectively, and agrees with archaeology. According to new data obtained, the time of the Tuekta-1 barrow construction is some years older than has been accepted thus far by archaeologists.
    • Chemistry Strategies for Organic 14C Samples

      Van Klinken, G. J.; Hedges, R. M. (Department of Geosciences, The University of Arizona, 1998-01-01)
      Pretreatment of organic samples can be achieved by removal of contaminants, or, alternatively, by isolation of sample-specific components. We discuss the molecular aspects of these two pretreatment types, together with an assessment of their effectiveness in relation to sample type. The main division in sample type is the one between carbohydrates and proteins, leading to opposite chemical strategies for the two sample categories. Recommendations for routine 14C chemistry of organic samples also include the standardization of quality screening procedures using chemical, stable isotope and elemental data that can be collected routinely during the pretreatment of each sample.