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| Titel |
Progress on using deuteron-deuteron fusion generated neutrons for ⁴⁰Ar/³⁹Ar sample irradiation |
| VerfasserIn |
Daniel Rutte, Paul R. Renne, Tim Becker, Cory Waltz, Mauricio Ayllon Unzueta, Susan Zimmerman, Alan Hidy, Robert Finkel, Joseph D. Bauer, Lee Bernstein, Karl van Bibber |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250145842
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| Publikation (Nr.) |
 EGU/EGU2017-9815.pdf |
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| Zusammenfassung |
| We present progress on the development and proof of concept of a deuteron-deuteron fusion
based neutron generator for 40Ar/39Ar sample irradiation. Irradiation with deuteron-deuteron
fusion neutrons is anticipated to reduce Ar recoil and Ar production from interfering
reactions. This will allow dating of smaller grains and increase accuracy and precision of the
method.
The instrument currently achieves neutron fluxes of ∼9×107 cm−2s−1 as determined by
irradiation of indium foils and use of the activation reaction 115In(n,n’)115mIn. Multiple foils
and simulations were used to determine flux gradients in the sample chamber. A first
experiment quantifying the loss of 39Ar is underway and will likely be available at the time of
the presentation of this abstract.
In ancillary experiments via irradiation of K salts and subsequent mass spectrometric
analysis we determined the cross-sections of the 39K(n,p)39Ar reaction at ∼2.8 MeV to be
160 ± 35 mb (1σ). This result is in good agreement with bracketing cross-section data of
∼96 mb at ∼2.45 MeV and ∼270 mb at ∼4 MeV [Johnson et al., 1967; Dixon and Aitken,
1961 and Bass et al. 1964]. Our data disfavor a much lower value of ∼45 mb at
2.59 MeV [Lindström & Neuer, 1958]. In another ancillary experiment the cross
section for 39K(n,α)36Cl at ∼2.8 MeV was determined as 11.7 ± 0.5 mb (1σ), which
is significant for 40Ar/39Ar geochronology due to subsequent decay to 36Ar as
well as for the determination of production rates of cosmogenic 36Cl. Additional
experiments resolving the cross section functions on 39K between 1.5 and 3.6 MeV
are on their way using the LICORNE neutron source of the IPN Orsay tandem
accelerator. Results will likely be available at the time of the presentation of this
abstract.
While the neutron generator is designed for fluxes of ∼109 cm−2s−1, arcing in the
sample chamber currently limits the power—straightforwardly correlated to the neutron
flux—the generator can safely be run at. Further technical improvements are necessary to
increase the neutron flux to make geologic sample irradiation possible in a reasonable
experimental timeframe.
(This work was performed under the auspices of the U.S. Department of Energy (DOE)
by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344, and by
the DOE Office of Science, Office of Nuclear Physics under Contract No. DE-AC02-
05CH11231 (LBNL).) |
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