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  • 11
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    Comparative AMS radiocarbon dating of pretreated versus non-pretreated tropical wood samples (2009)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 268 (2010): 910-913, doi:10.1016/j.nimb.2009.10.062.
    Description: Several wood samples collected from Dorslandboom, a large African baobab (Adansonia digitata L.) from Namibia, were investigated by AMS radiocarbon dating subsequent to pretreatment and, alternatively, without pretreatment. The comparative statistical evaluation of results showed that there were no significant differences between fraction modern values and radiocarbon dates of the samples analyzed after pretreatment and without pretreatment, respectively. The radiocarbon date of the oldest sample was 993 ± 20 BP. Dating results also revealed that Dorslandboom is a multi-generation tree, with several stems showing different ages.
    Description: This material is based on work supported by U.S. National Science Foundation under Cooperative Agreement OCE-022828996. Part of the research was supported by grants from the Romanian Academy and the Romanian National University Research Council (PN II – ID 2354) and also by Nova Research Inc.
    Keywords: AMS C-14 dating ; Tropical trees ; Adansonia digitata ; Gas ion source ; Pretreatment
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 12
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    A continuous-flow gas chromatography 14C accelerator mass spectrometry system (2011)
    Dept. of Geosciences, University of Arizona
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Arizona Board of Regents on behalf of the University of Arizona, 2010. This article is posted here by permission of Dept. of Geosciences, University of Arizona for personal use, not for redistribution. The definitive version was published in Radiocarbon 52 (2010): 295-300.
    Description: 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 compoundspecific 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.
    Description: This work was performed under NSF Cooperative Agreement Number OCE-0753487.
    Repository Name: Woods Hole Open Access Server
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  • 13
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    Age and growth rate dynamics of an old African baobab determined by radiocarbon dating (2011)
    Dept. of Geosciences, University of Arizona
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Arizona Board of Regents on behalf of the University of Arizona, 2010. This article is posted here by permission of Dept. of Geosciences, University of Arizona for personal use, not for redistribution. The definitive version was published in Radiocarbon 52 (2010): 727-734.
    Description: 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.
    Description: This material is based on work supported by a grant from the Romanian National University Research Council (PN II - IDEI 2354 Nr. 1092) and by US National Science Foundation under Cooperative Agreement OCE-022828996.
    Repository Name: Woods Hole Open Access Server
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  • 14
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    A gas-accepting ion source for Accelerator Mass Spectrometry : progress and applications (2013)
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 294 (2013): 296-299, doi:10.1016/j.nimb.2011.10.016.
    Description: The National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility at the Woods Hole Oceanographic Institution has developed an Accelerator Mass Spectrometry (AMS) system designed specifically for the analysis of 14C in a continuously flowing stream of carrier gas. A key part of the system is a gas-accepting microwave ion source. Recently, substantial progress has been made in the development of this source, having achieved ion currents rivaling that of a traditional graphite source (albeit at relatively low efficiency). Details and present performance of the gas source are given. Additionally, representative results obtained from coupling the source to both a gas chromatograph and gas bench are presented.
    Description: This work is supported by a Cooperative Agreement (OCE- 2310753487) with the US National Science Foundation.
    Repository Name: Woods Hole Open Access Server
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  • 15
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    Carbonate as sputter target material for rapid 14C AMS (2013)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 294 (2013): 328-334, doi:10.1016/j.nimb.2012.05.014.
    Description: This paper describes a technique for measuring the 14C content of carbonate samples by producing C-ions directly in the negative ion sputter source of an accelerator mass spectrometer (AMS) system. This direct analysis of carbonate material eliminates the time and expense of graphite preparation. Powdered carbonate is mixed with titanium powder, loaded into a target cartridge, and compressed. Beam currents for optimally sized carbonate targets (0.09-0.15 mg C) are typically 10-20% of those produced by optimally-sized graphite targets (0.5-1 mg C). Modern (〉0.8 Fm) samples run by this method have standard deviations of 0.009 Fm or less, and near-modern samples run as unknowns agree with values from traditional hydrolysis/graphite to better than 2%. Targets with as little as 0.06 mg carbonate produce useable ion currents and results, albeit with increased error and larger blank. In its current state, direct sputtering is best applied to problems where a large number of analyses with lower precision are required. These applications could include age surveys of deep-sea corals for determination of historic population dynamics, to identify samples that would benefit from high precision analysis, and for growth rate studies of organisms forming carbonate skeletons.
    Description: This work was funded by a WHOI Mellon Interdisciplinary award, NSF NOSAMS cooperative agreement, and NSF OPP #s 0944474 and 0902957.
    Repository Name: Woods Hole Open Access Server
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  • 16
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    Optimizing a microwave gas ion source for continuous-flow accelerator mass spectrometry (2012)
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of American Institute of Physics for personal use, not for redistribution. The definitive version was published in Review of Scientific Instruments 83 (2012): 02B304, doi:10.1063/1.3656408.
    Description: A 2.45 GHz microwave ion source coupled with a magnesium charge exchange canal (CxC) has been successfully adapted to a large acceptance radiocarbon accelerator mass spectrometry system at the National Ocean Sciences AMS Facility (NOSAMS), Woods Hole Oceanographic Institution. CO2 samples from various preparation sources are injected into the source through a glass capillary at 370 µl/min. Routine system parameters are about 120 - 140 µA of negative 12C current after the CxC, leading to about 400 14C counts per second for a modern sample and implying a system efficiency of 0.2%. While these parameters already allow us to perform high quality AMS analyses on large samples, we are working on ways to improve the output of the ion source regarding emittance and efficiency. Modeling calculations suggest modifications in the extraction triode geometry, shape and size of the plasma chamber could improve emittance and hence ion transport efficiency. Results of experimental tests of these modifications are presented.
    Description: This work has been supported by the US National Science Foundation through Cooperative Agreement OCE-0753487.
    Repository Name: Woods Hole Open Access Server
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  • 17
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    Design and reality : continuous-flow accelerator mass spectrometry (CFAMS) (2012)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 269 (2011): 3176–3179, doi:10.1016/j.nimb.2011.04.019.
    Description: In 2007 we published the design of a novel accelerator mass spectrometry (AMS) system capable of analyzing gaseous samples injected continuously into a microwave plasma gas ion source. Obvious advantages of such a system are drastically reduced processing times and avoidance of potentially contaminating chemical preparation steps. Another paper in these proceedings will present the progress with the development of the microwave gas ion source that has since been built and tested at the National Ocean Sciences AMS Facility in Woods Hole. In this paper we will review the original design and present updates, reflecting our recent encouraging experience with the system. A simple summary: large acceptance ion beam optics design is beneficial to accelerator mass spectrometry in general, but essential to AMS with plasma gas ion sources.
    Keywords: Ion optics ; Computer modeling ; Microwave ion source ; Continuous-flow AMS
    Repository Name: Woods Hole Open Access Server
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  • 18
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    Single Step Production of Graphite from Organic Samples [Poster] (2018)
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    Publication Date: 2022-05-25
    Description: We present a low-cost, high-throughput method for converting many types of organic samples into graphite. The method combines sample combustion and graphitization in a single process. Using a modified sealed graphitization method, samples are placed in a Pyrex tube containing zinc, titanium hydride and iron catalyst. The tube is evacuated, flamed sealed, and placed in a muffle furnace for 7 hours. Graphite forms on the iron and is then analyzed for 14C content using either of NOSAMS’s two AMS systems. This method has been shown to work on a variety of organic samples including pure compounds, wood, peat, collagen and humics. This simplified procedure could be especially useful in reconnaissance studies in which it is desired to rapidly measure a large number of samples (untreated or pretreated), at low-cost with analytical precision and accuracy approaching that of traditional hydrogen reduction methods.
    Keywords: Beech Tree ; Graphite
    Repository Name: Woods Hole Open Access Server
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  • 19
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    Accelerator mass spectrometry 14C determination in CO2 produced from laser decomposition of aragonite (2009)
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © John Wiley & Sons, 2008. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Rapid Communications in Mass Spectrometry 22 (2008): 3443-3449, doi:10.1002/rcm.3745.
    Description: Determination of 14C in aragonite (CaCO3) decomposed thermally to CO2 using an yttrium‐aluminum‐garnet doped neodymium laser is reported. Laser decomposition accelerator mass spectrometer (LD‐AMS) measurements reproduce AMS determinations of 14C from conventional reaction of aragonite with concentrated phosphoric acid. The lack of significant differences between these sets of measurements indicate that LD‐AMS radiocarbon dating can overcome the significant fractionation that has been observed during stable isotope (C and O) laser decomposition analysis of different carbonate minerals. The laser regularly converted nearly 30% of material removed to CO2 despite being optimized for ablation, where laser energy breaks material apart rather than chemically altering it. These results illustrate promise for using laser decomposition on the front‐end of AMS systems that directly measure CO2 gas. The feasibility of such measurements depends on 1. the improvement of material removal and/or CO2 generation efficiency of the laser decomposition system and 2. the ionization efficiency of AMS systems measuring continuously flowing CO2.
    Description: This work was funded on a competitive basis by the Cecil H. and Ida M. Green Technology Innovation Award of Woods Hole Oceanographic Institution.
    Repository Name: Woods Hole Open Access Server
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  • 20
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    Ultra-small graphitization reactors for ultra-microscale 14C analysis at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) Facility (2015)
    University of Arizona Libraries
    Details
    Publication Date: 2022-05-26
    Description: © The Arizona Board of Regents on behalf of the University of Arizona, 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Radiocarbon 57, no. 1 (2015): 109–122, doi:10.2458/azu_rc.57.18118.
    Description: In response to the increasing demand for 14C analysis of samples containing less than 25 µg C, ultra-small graphitization reactors with an internal volume of ~0.8 mL were developed at NOSAMS. For samples containing 6 to 25 µg C, these reactors convert CO2 to graphitic carbon in approximately 30 min. Although we continue to refine reaction conditions to improve yield, the reactors produce graphite targets that are successfully measured by AMS. Graphite targets produced with the ultra-small reactors are measured by using the Cs sputter source on the CFAMS instrument at NOSAMS where beam current was proportional to sample mass. We investigated the contribution of blank carbon from the ultra-small reactors and estimate it to be 0.3 ± 0.1 µg C with an Fm value of 0.43 ± 0.3. We also describe equations for blank correction and propagation of error associated with this correction. With a few exceptions for samples in the range of 6 to 7 µg C, we show that corrected Fm values agree with expected Fm values within uncertainty for samples containing 6–100 µg C.
    Description: This work was funded by the NSF Cooperative Agreement for the Operation of a National Ocean Sciences Accelerator Mass Spectrometry Facility (OCE-0753487). S R Shah Walter was also partially supported by the WHOI Postdoctoral Scholar Program.
    Keywords: Ultra-microscale ; Carbon dioxide ; Graphite ; Accelerator mass spectroscopy ; Methods ; Sample preparation
    Repository Name: Woods Hole Open Access Server
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