• A Beam Profile Monitor for Rare Isotopes in Accelerator Mass Spectrometry: Preliminary Measurements

      Taccetti, F.; Carraresi, L.; Fedi, M. E.; Manetti, M.; Mariani, P.; Tobia, G.; Mandò, P. A. (Department of Geosciences, The University of Arizona, 2010-01-01)
      In accelerator systems, beam lines are generally equipped with diagnostic elements, such as Faraday cups and beam profile monitors (BPM), to optimize beam transport. These diagnostic elements, or at least commercial ones, are designed to only work with continuous beams, and their typical maximum sensitivity is about few tens of pA. Thus, in the case of diagnosis of rare isotope beams in accelerator mass spectrometry (AMS), Faraday cups and BPMs are not suitable on the high-energy side of the tandem accelerator, after energy-mass-charge analysis. For example, in 14C AMS, even for a modern sample, the expected counting rate is a few tens of Hz; in these conditions, a commercial BPM cannot be used. On the other hand, checking the shape and the position of the rare isotope beam hitting the detector can be important in order to better identify signals in the detector itself, thus also helping in reducing the measurement background. This paper presents a prototype BPM especially designed for low-intensity beams. The BPM is based on a multiwire proportional chamber characterized by 2 grids of anode wires, oriented perpendicular to each other in order to measure both the x and the y coordinates of the particle impact point. Details about the design and the electronics of the device are given, and the first test measurements are discussed.
    • A Comparison of Cellulose Extraction and ABA Pretreatment Methods for AMS 14C Dating of Ancient Wood

      Southon, J. R.; Magana, A. L. (Department of Geosciences, The University of Arizona, 2010-01-01)
      We have compared accelerator mass spectrometry (AMS) radiocarbon results on wood samples at or near the limit of 14C dating, pretreated with a standard acid-base-acid (ABA) protocol, with those obtained from cellulose prepared from the same samples by several modifications of the Jayme-Wise cellulose extraction method (Green 1963). These tests were carried out to determine the most efficient way to ensure low backgrounds in 14C measurements of well-preserved ancient wood samples.
    • A Continuous-Flow Gas Chromatography 14C Accelerator Mass Spectrometry System

      McIntyre, C. P.; Galutschek, E.; Roberts, M. L.; von Reden, K. F.; McNichol, A. P.; Jenkins, W. J. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Gas-accepting ion sources for radiocarbon accelerator mass spectrometry (AMS) have permitted the direct analysis of CO2 gas, eliminating the need to graphitize samples. As a result, a variety of analytical instruments can be interfaced to an AMS system, processing time is decreased, and smaller samples can be analyzed (albeit with lower precision). We have coupled a gas chromatograph to a compact 14C AMS system fitted with a microwave ion source for real-time compound-specific 14C analysis. As an initial test of the system, we have analyzed a sample of fatty acid methyl esters and biodiesel. Peak shape and memory was better then existing systems fitted with a hybrid ion source while precision was comparable. 14C/12C ratios of individual components at natural abundance levels were consistent with those determined by conventional methods. Continuing refinements to the ion source are expected to improve the performance and scope of the instrument.
    • A High-Performance 14C Accelerator Mass Spectrometry System

      Roberts, M. L.; Burton, J. R.; Elder, K. L.; Longworth, B. E.; McIntyre, C. P.; Vo, K. F.; Han, B. X.; Rosenheim, B. E.; Jenkins, W. J.; Galutschek, E.; et al. (Department of Geosciences, The University of Arizona, 2010-01-01)
      A new and unique radiocarbon accelerator mass spectrometry (AMS) facility has been constructed at the Woods Hole Oceanographic Institution. The defining characteristic of the new system is its large-gap optical elements that provide a larger-than-standard beam acceptance. Such a system is ideally suited for high-throughput, high-precision measurements of 14C. Details and performance of the new system are presented.
    • A New 14C Data Set of the PY608W-PC Sediment Core from Lake Pumoyum Co (Southeastern Tibetan Plateau) over the Last 19 kyr

      Watanabe, Takahiro; Matsunaka, Tetsuya; Nakamura, Toshio; Nishimura, Mitsugu; Izutsu, Yasuhiro; Minami, Motoyasu; Nara, Fumiko Watanabe; Kakegawa, Takeshi; Zhu, Liping (Department of Geosciences, The University of Arizona, 2010-01-01)
      A new continuous sediment core (PY608W-PC; 3.8 m length) for reconstruction of climatic and environmental changes in the southeastern Tibetan Plateau was taken from the eastern part of Lake Pumoyum Co in August 2006. Sediment layers of the lower part of PY608W-PC (380-300 cm depth) were composed mainly of relatively large plant residues (up to ~3 cm in length) with an admixture of fine sand and sandy silt. The large plant residues disappeared at ~300-290 cm depth in core PY608W-PC and were replaced by silt-silty clay. The large plant residues from the lower part of PY608W-PC could be aquatic, because the plant residues were extremely enriched in 13C (up to -3.0‰, -5.6 +/- 2.3‰ on average). On the other hand, the plant residue concentrates (PRC fractions) from the upper part of the core (290-0 cm in depth) could be terrestrial C3 plants (delta-13C = -21.8 +/- 1.7 on average). Radiocarbon dating was performed on the large plant residues and PRC fractions from the PY608W-PC sediment core, which represented the chronology from ~19,000 cal BP to present.
    • A New 1MV AMS Facility at KIGAM

      Hong, W.; Park, J. H.; Sung, K. S.; Woo, H. J.; Kim, J. K.; Choi, H. W.; Kim, G. D. (Department of Geosciences, The University of Arizona, 2010-01-01)
      A 1MV AMS was installed in KIGAM (Korea Institute of Geoscience and Mineral Resources). After 4 months of installation, the AMS started normal operation from January 2008. This multi-element AMS was developed by HVEE to measure 14C, 10Be, and 26Al. The results of an acceptance test demonstrate that this machine is capable of routine 14C age dating and of measurements of other radioisotopes in terms of accuracy and precision as well as the background level. After installation, an investigation aimed at determining the stable operating conditions was conducted, and background levels were determined to be as low as 10-15 for 14C and 10-14 for 10Be and 26Al.
    • A New Attempt to Establish the International Radiocarbon Soils Database (IRSDB)

      Becker-Heidmann, Peter; Heidmann, Pascal (Department of Geosciences, The University of Arizona, 2010-01-01)
      Twenty years after the first International Radiocarbon Database Workshop, and 13 yr after the setup of a preliminary structure for a worldwide database on 14C dates of soils, sound reasons and excuses for not establishing a real and globally accessible database have diminished. Climate change itself is widely accepted as reality now, and the strong demand of the modeling community for reliable data of the carbon pool--especially in soils--has been maintained. With the steadily increasing capacity of 14C dating facilities, these data can be and are produced. Nevertheless, they still cannot be accessed easily and equally enough. Now, decreased costs of hardware and recent developments of the internet enable the IRSDB to be implemented, in a joint effort. As a seed, a test server has been set up, with open-source software, housing the database in alpha-stage, a web interface, and a community portal. Thus, the development of the design as well as the data input of the database is done in close collaboration of the users of the database, the laboratories, soil scientists, archaeologists, modelers, other scientists, and interested laypersons. In order to guarantee the longtime independence of the availability and usability of the database from vendors or changing standards, only widely used open-source software and open standards are used. Therefore, the development of plug-ins for data input from laboratory databases or output to different required formats as well as interfaces to GIS and other software is possible. A version control system takes care of the integrity of the data.
    • A New Automated Extraction System for 14C Measurement for Atmospheric CO2

      Turnbull, Jocelyn C.; Lehman, Scott J.; Morgan, Stephen; Wolak, Chad (Department of Geosciences, The University of Arizona, 2010-01-01)
      The radiocarbon content of atmospheric CO2 (∆14CO2) has long been of interest to atmospheric and Earth system researchers. Recent improvements in 14C measurement precision and reduction in sample size requirements have now made it possible to measure ∆14CO2 within existing trace gas sampling networks, most notably as a method to quantify recently added fossil-fuel-derived CO2 in the atmosphere. At INSTAAR, in collaboration with NOAA/ESRL, ~600 atmospheric samples from around the globe are prepared each year, and that number is anticipated to grow in connection with various monitoring and data assimilation efforts. To accommodate the growing demand and reduce per sample costs, we developed an automated extraction system to quantitatively isolate CO2 from whole air for AMS 14C analysis. Twenty samples can be extracted in 1 fully automated run, taking 10-12 hr to complete and requiring only about 1 hr of operator time, a substantial improvement over the manual extraction system. CO2 is extracted cryogenically by flowing the whole air over a liquid nitrogen trap, after first removing water in a trap at -85 C. Large volume vacuum lines are used to extract ~30 mol of CO2 in less than 10 min, keeping contamination from leaks to a minimum and allowing rapid processing and greater throughput. 13C measurements on the resultant CO2 demonstrate that extraction is quantitative, and extractions of 14C-free air show that no significant modern contamination occurs. Replicate analyses of standard materials indicate that both mean values and precision are comparable to those for the manual extraction system.
    • A New Radiocarbon Pretreatment Method for Molluscan Shell Using Density Fractionation of Carbonates in Bromoform

      Russo, Christopher M.; Tripp, Jennifer A.; Douka, Katerina; Higham, Thomas F. G. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Coastal archaeological sites that lack organic remains for radiocarbon dating are often abundant sources of molluscan shells. As a substitute for materials such as bone and charcoal, shells can be analyzed with 14C dating to determine a site's age. Despite their being convenient, non-mobile archaeological artifacts, molluscan shells are plagued by several issues, including carbonate remodeling, in which aragonite in shells is converted to calcite as predicted by thermodynamics. We present here a carbonate density separation technique that addresses the issue of carbonate remodeling. Using a density fractionation with bromoform, aragonite concentrations are enriched in shells that have undergone significant remodeling. The technique has been applied to archaeological shells and has returned dates that are younger than those previously determined for the same shells.
    • A Nondestructive Prescreening Method for Bone Collagen Content Using Micro-Computed Tomography

      Tripp, J. A.; Squire, M. E.; Hamilton, J.; Hedges, R. E. M. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Isolation of bone collagen for radiocarbon dating is a labor-intensive and time-consuming process that sometimes results in unacceptably low protein recovery. In preliminary studies reported here, micro-computed tomography (microCT), a nondestructive technique that uses X-rays to produce high-resolution three-dimensional images of mineralized materials such as bone, offers promise as a suitable prescreening option for bones of questionable preservation. We have found that the bone volume fraction calculated by the scanner software correlates well with collagen recovery in 4 analyzed bones from Etton, United Kingdom.
    • A Preparative 2D-Chromatography Method for Compound-Specific Radiocarbon Analysis of Dicarboxylic Acids in Aerosols

      Fahrni, S. M.; Ruff, M.; Wacker, L.; Perron, N.; Gäggeler, H. W.; Szidat, S. (Department of Geosciences, The University of Arizona, 2010-01-01)
      There is a great scientific demand for an assessment of the sources and formation processes of atmospheric carbonaceous aerosols since they strongly influence the global radiation balance and affect public health. Much attention in atmospheric studies has been paid to dicarboxylic acids (DCAs) due to their abundance at substantially different sites and their potential influence on cloud formation processes. Nevertheless, sources of oxalic acid (HOOCCOOH) and other DCAs are not well understood yet. In order to quantify contributions of fossil and non-fossil sources, a method for the preparative separation of oxalic acid and other DCAs from aerosols for compound-specific radiocarbon analysis (CSRA) has been developed. This method consists of a water extraction of aerosols collected on quartz-fiber filters followed by 2 consecutive liquid chromatography (LC) steps on different chromatography columns (2D-chromatography). Through the use of aqueous, completely non-organic eluents and single injections into liquid chromatography, low blank levels are achieved with total oxalic acid recoveries of up to 66%. Upon separation, 14C measurements of small samples (containing typically 10-20 g carbon) are conducted at the gas ion source of the 200kV accelerator mass spectrometry facility MICADAS. The method is verified with processed reference materials, artificial mixtures of oxalic acid with typical matrix components, and a standard addition of ambient aerosols. Two exemplary field samples show dominant non-fossil sources of oxalic acid.
    • A Report on Phase 2 of the Fifth International Radiocarbon Intercomparison (VIRI)

      Scott, E. Marian; Cook, Gordon T.; Naysmith, Philip (Department of Geosciences, The University of Arizona, 2010-01-01)
      The Fifth International Radiocarbon Intercomparison (VIRI) continues the tradition of the TIRI (third) and FIRI (fourth) (Scott 2003) intercomparisons and operates in addition to any within-laboratory quality assurance measures as an independent check on laboratory procedures. VIRI is a phased intercomparison; results for the first phase, which employed grain samples, were reported in Scott et al. (2007). The second phase, involving bone samples, is reported here. The third and final phase, which includes samples of peat, wood, and shell, has also been completed and a companion paper appears in these proceedings. Five bone samples were made available and included Sample E: mammoth bone (>5 half-lives); Sample F: horse bone (from Siberia, excavated in 2001; and Samples H and I: whale bones (approximately 2 half-lives). Sample G (human bone) was accessible only to accelerator mass spectrometry (AMS) laboratories because of the limited amount of sample available. More than 40 laboratories participated in Phase 2 and consensus values for the ages were as follows: Sample E = 39,305 14C yr BP (standard deviation [1 sigma] = 121 yr); Sample F = 2513 yr BP (1 sigma = 5 yr); Sample G = 969 yr BP (1 sigma = 5 yr); Sample H = 9528 yr BP (1 sigma = 7 yr); and Sample I = 8331 yr BP (1 sigma = 6 yr). Sample G had previously been dated by 4 laboratories and a weighted mean of 934 +/- 12 yr BP had been quoted. Sample I had previously been dated at 8335 +/- 25 yr BP and Sample H had been dated at 9565 +/- 130 yr BP. Results for Sample H and Sample I are in good agreement with the previous results; Sample G results, however, give a value that is significantly older than the previously reported results.
    • A Response to Finkelstein and Piasetzky's Criticism and "New Perspective"

      Mazar, Amihai; Bronk Ramsey, Christopher (Department of Geosciences, The University of Arizona, 2010-01-01)
      The following short paper is a response to criticism by Finkelstein and Piasetzky (2010b), published in the present issue of Radiocarbon, of our 2008 paper in Radiocarbon concerning the evaluation of 14C dates from Iron Age levels in Israel published by Boaretto et al. (2005). We refer to criticism concerning exclusion and inclusion of data. We also evaluate new models suggested by Finkelstein and Piasetzky and in particular their suggestion of regional stages marking the end of the Iron Age in Israel. We also comment on several methodological issues.
    • A Simplified In Situ Cosmogenic 14C Extraction System

      Pigati, Jeffrey S.; Lifton, Nathaniel A.; Jull, A. J. Timothy; Quade, Jay (Department of Geosciences, The University of Arizona, 2010-01-01)
      We describe the design, construction, and testing of a new, simplified in situ radiocarbon extraction system at the University of Arizona. Blank levels for the new system are low ((234 +- 11) x 10^3 atoms (1 sigma; n = 7)) and stable. The precision of a given measurement depends on the concentration of 14C, but is typically <5% for concentrations of 100 x 10^3 atoms g^(-1) or more. The new system is relatively small and easy to construct, costs significantly less than the original in situ 14C extraction system at Arizona, and lends itself to future automation.
    • A Thermal and Acid Treatment for Carbon Extraction from Cast Iron and Its Application to AMS Dating of Cast Iron Objects from Ancient Korea

      Park, J. S.; Burr, G. S.; Jull, A. J. T. (Department of Geosciences, The University of Arizona, 2010-01-01)
      A method of thermal and acid treatments was developed at the Archaeo-metallurgy Laboratory of Hongik University in Korea to extract carbon from cast iron, and carbon objects thus prepared from cast iron artifacts of ancient Korea were dated at the University of Arizona's AMS Facility. The thermal treatments consist of heating a specimen to ~1000 C in a controlled environment with reduced oxygen potential, then cooling it rapidly to room temperature. The heating causes the cementite phase in white cast iron to be graphitized and the quenching suppresses pearlite formation. The specimen then consists of flakes of graphite embedded in a matrix of martensite. The next stage of the treatment is to dissolve the martensite matrix in a solution of nitric and hydrochloric acids to release the graphite as a powder. This material is then cleaned, dried, and pressed into target holders for accelerator mass spectrometry (AMS) analysis. The method was applied to a collection of artifacts from the Korean Three Kingdoms period (about AD 300-668) and the AMS results were compared with chronological estimates from other means.
    • A Wiggle-Matched Date for the Copper Age Cemetery at Manerba del Garda, Northern Italy

      Barfield, Lawrence H.; Manning, Sturt W.; Valzolgher, Erio; Higham, Thomas F. G. (Department of Geosciences, The University of Arizona, 2010-01-01)
      The cemetery in the Riparo Valtenesi rockshelter at Manerba del Garda in northern Italy is well known for its wooden burial chambers. These chambers are some of the best sources of evidence for 3rd millennium BC collective burial in Europe. To further refine the absolute dating of burial activity at the site (beyond the approximate data provided by a previous series of routine radiocarbon measurements), a charred construction oak timber was sampled from Chamber 133 for 14C dendro wiggle-matching (DWM). We present the results from the DWM analysis, the first of its kind for the Italian Copper Age as a whole, establishing a terminus post quem for construction of Chamber 133 ~2955-2872 cal BC.
    • Age and Growth Rate Dynamics of an Old African Baobab Determined by Radiocarbon Dating

      Patrut, A.; Mayne, D. H.; Vo, K. F.; Lowy, D. A.; Venter, S.; McNichol, A. P.; Roberts, M. L.; Margineanu, D. (Department of Geosciences, The University of Arizona, 2010-01-01)
      In 2008, a large African baobab (Adansonia digitata L.) from Makulu Makete, South Africa, split vertically into 2 sections, revealing a large enclosed cavity. Several wood samples collected from the cavity were processed and radiocarbon dated by accelerator mass spectrometry (AMS) for determining the age and growth rate dynamics of the tree. The 14C date of the oldest sample was found to be of 1016 22 BP, which corresponds to a calibrated age of 1000 15 yr. Thus, the Makulu Makete tree, which eventually collapsed to the ground and died, becomes the second oldest African baobab dated accurately to at least 1000 yr. The conventional growth rate of the trunk, estimated by the radial increase, declined gradually over its life cycle. However, the growth rate expressed more adequately by the cross-sectional area increase and by the volume increase accelerated up to the age of 650 yr and remained almost constant over the past 450 yr.
    • Age-Depth Model of Lake Soppensee (Switzerland) Based on the High-Resolution 14C Chronology Compared with Varve Chronology

      Hajdas, Irka; Michczyński, Adam (Department of Geosciences, The University of Arizona, 2010-01-01)
      An age-depth model for laminated sediments of Lake Soppensee is constructed using radiocarbon ages of macrofossils and a depositional model of the OxCal v 4.1 program with the updated IntCal09 data set. The resulting calendar chronology is compared with the varve chronology that was built for this record in a previous study (Hajdas 1993); there is a very good agreement between the 2 approaches. This illustrates the potential of high-resolution 14C dating for construction of reliable, high-resolution calendar timescales for sedimentary records. Based on the age-depth model of this study, the Vasset/Killian tephra found in sediment of Soppensee dates to a calendar age of 9291-9412 cal BP (2-delta range) while the Lachersee tephra dates to 12,735-12,871 cal BP (2-delta range). Precise dating of the Late Glacial boundaries is possible with this chronology but requires more precise correlation between proxies and records than typically practiced.
    • Alternative Explanations for Anomalous 14C Ages on Human Skeletons Associated with the 612 BCE Destruction of Nineveh

      Taylor, R. E.; Beaumont, W. C.; Southon, J.; Stronach, D.; Pickworth, D. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Three factors--contamination, a dietary reservoir effect, and a regional ∆14C anomaly--are considered as possible contributing explanations for an almost 2-century offset between the historically documented age of 612 BCE and the calibrated ages of 9 14C determinations obtained on 3 human skeletons directly associated stratigraphically with an archaeologically--and historically--defined 612 BCE event at the ancient site of Nineveh in northern Mesopotamia (Iraq). We note that on the order of a 1% (~80 yr) offset caused by one or a combination of these 3 factors, or other as yet unidentified additional factor(s), would be sufficient to move the average measured 14C age of these bone samples within the major "warp" in the 14C timescale during the mid-1st millennium BCE. We provide what we believe to be sufficient evidence that contamination is not a major factor in the case of these bone samples. At this time, we lack appropriate data to determine with sufficient rigor the degree to which a dietary reservoir effect may be contributing to the offset. At present, a posited regional ∆14C anomaly does not appear to be supported on the basis of data from several other localities in the Near East of similar age. One purpose of presenting this data set is to solicit comparisons with 14C values obtained on samples from additional, historically well-documented, known-age archaeological contexts for this time period in this and adjacent regions.
    • Alternative Methods for Cellulose Preparation for AMS Measurement

      Němec, Mojmir; Wacker, Lukas; Hajdas, Irka; Gäggeler, Heinz (Department of Geosciences, The University of Arizona, 2010-01-01)
      The main methods applied to clean plant material for radiocarbon dating are not compound-specific and generally remove only the easily exchangeable components by an acid-base-acid sequence and additional optional steps like Soxhlet extraction to remove resins and oxidative bleaching with NaClO2. The products are normally clean enough for standard 14C measurement, but in some cases it is desirable to have pure cellulose, which remains unchanged and immobile over longer time ranges, better representing the original plant material. In this work, 2 more compound-specific but still simple methods were tested to separate the cellulose from wood. The viscose method is based on the xanthification process used in the textile industry, where the alkali-cellulose with CS2 forms a soluble cellulose xanthate, which is then extracted and cellulose is recovered. The second procedure is based on the wood/cellulose dissolution in ionic liquid 1-butyl-3-methylimidazolium chloride [BMIM]Cl, when the dissolved cellulose could be precipitated again by simply adding a water-acetone mixture. This process was recently reported, but still not used in sample preparation procedures for 14C dating.