Burton Joshua R.

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Burton
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Joshua R.
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Author: Beaupre, Steven R. ×

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  • 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
    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.
  • 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.