Burton Joshua R.

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Joshua R.

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  • Preprint
    Progress with a gas-accepting ion source for Accelerator Mass Spectrometry
    ( 2010-08) Roberts, Mark L. ; von Reden, Karl F. ; McIntyre, Cameron P. ; Burton, Joshua R.
    The National Ocean Sciences AMS (NOSAMS) facility at Woods Hole Oceanographic Institution has developed a novel, gas-accepting microwave-plasma ion-source. The source is a key component of a compact Accelerator Mass Spectrometry (AMS) system built for the analysis of 14C in a continuously flowing gas stream. The gas source produces carbon currents from a stream of CO2 with currents typical of a traditional graphite source. Details of the gas source, including ion current achieved, optimal flow rate, efficiency, and memory are presented. Additionally, data obtained from coupling a gas chromatograph to the source to will be shown.
  • Preprint
    Rapid, high-resolution C-14 chronology of ooids
    ( 2015-03) Beaupre, Steven R. ; Roberts, Mark L. ; Burton, Joshua R. ; Summons, Roger E.
    Ooids are small, spherical to ellipsoidal grains composed of concentric layers of CaCO3 that could potentially serve as biogeochemical records of the environments in which they grew. Such records, however, must be placed in the proper temporal context. Therefore, we developed a novel acidification system and employed an accelerator mass spectrometer (AMS) with a gas accepting ion source to obtain radiocarbon (14C) chronologies extending radially through ooids within one 8-hour workday. The method was applied to ooids from Highborne Cay, Bahamas and Shark Bay, Australia, yielding reproducible 14C chronologies, as well as constraints on the rates and durations of ooid growth and independent estimates of local 14C reservoir ages.
  • Preprint
    Design and reality : continuous-flow accelerator mass spectrometry (CFAMS)
    ( 2010-09) von Reden, Karl F. ; Roberts, Mark L. ; McIntyre, Cameron P. ; Burton, Joshua R.
    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.
  • Preprint
    Optimizing a microwave gas ion source for continuous-flow accelerator mass spectrometry
    ( 2011-09) von Reden, Karl F. ; Roberts, Mark L. ; Burton, Joshua R. ; Beaupre, Steven R.
    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.
  • Article
    Advances in Sample Preparation at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS): Investigation of Carbonate Secondary Standards
    ( 2017) Cruz, Anne J. ; Childress, Laurel B. ; Gagnon, Alan R. ; McNichol, Ann P. ; Burton, Joshua R. ; Elder, Kathryn L. ; Lardie Gaylord, Mary C. ; Gospodinova, Kalina D. ; Hlavenka, Joshua ; Kurz, Mark D. ; Longworth, Brett E. ; Roberts, Mark L. ; Trowbridge, Nan Y. ; Walther, Tess ; Xu, Li
    The development of robust sample preparation techniques for ocean science research has been a hallmark of NOSAMS since its inception. Improvements to our standard methods include reducing the minimum size of the samples we can analyze, building modular graphite reactors of different sizes that we can swap in and out depending on our sample stream, and modifying our carbonate acidification methods to improve handling of the smaller samples we now receive. A relatively new instrument, the Ramped PyrOx, which allows the separation of organic matter into thermal fractions, has attracted much interest as a research and development tool. We will also discuss our progress on incorporating a Picarro isotope analyzer into our sample preparation options.
  • Article
    A high-performance 14C accelerator mass spectrometry system
    (Dept. of Geosciences, University of Arizona, 2010-08) Roberts, Mark L. ; Burton, Joshua R. ; Elder, Kathryn L. ; Longworth, Brett E. ; McIntyre, Cameron P. ; von Reden, Karl F. ; Han, Baoxi ; Rosenheim, Brad E. ; Jenkins, William J. ; Galutschek, Ernst ; McNichol, Ann P.
    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.
  • Article
    Rapid radiocarbon (14C) analysis of coral and carbonate samples using a continuous-flow accelerator mass spectrometry (CFAMS) system
    (American Geophysical Union, 2011-11-05) McIntyre, Cameron P. ; Roberts, Mark L. ; Burton, Joshua R. ; McNichol, Ann P. ; Burke, Andrea ; Robinson, Laura F. ; von Reden, Karl F. ; Jenkins, William J.
    Radiocarbon analyses of carbonate materials provide critical information for understanding the last glacial cycle, recent climate history and paleoceanography. Methods that reduce the time and cost of radiocarbon (14C) analysis are highly desirable for large sample sets and reconnaissance type studies. We have developed a method for rapid radiocarbon analysis of carbonates using a novel continuous-flow accelerator mass spectrometry (CFAMS) system. We analyzed a suite of deep-sea coral samples and compared the results with those obtained using a conventional AMS system. Measurement uncertainty is <0.02 Fm or 160 Ryr for a modern sample and the mean background was 37,800 Ryr. Radiocarbon values were repeatable and in good agreement with those from the conventional AMS system. Sample handling and preparation is relatively simple and the method offered a significant increase in speed and cost effectiveness. We applied the method to coral samples from the Eastern Pacific Ocean to obtain an age distribution and identify samples for further analysis. This paper is intended to update the paleoceanographic community on the status of this new method and demonstrate its feasibility as a choice for rapid and affordable radiocarbon analysis.
  • Preprint
    A gas-accepting ion source for Accelerator Mass Spectrometry : progress and applications
    ( 2011-10-31) Roberts, Mark L. ; von Reden, Karl F. ; Burton, Joshua R. ; McIntyre, Cameron P. ; Beaupre, Steven R.
    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.