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Measurement and analysis of the Am243 neutron capture cross section at the n_TOF facility at CERN

E. Mendoza et al. (n_TOF Collaboration)
Phys. Rev. C 90, 034608 – Published 11 September 2014
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  • INTRODUCTION
  • THE EXPERIMENTAL SETUP
  • DATA REDUCTION
  • CROSS SECTION ANALYSIS
  • CONCLUSIONS
  • ACKNOWLEDGEMENTS
    • References

    Abstract

    Background: The design of new nuclear reactors and transmutation devices requires to reduce the present neutron cross section uncertainties of minor actinides.

    Purpose: Improvement of the Am243(n,γ) cross section uncertainty.

    Method: The Am243(n,γ) cross section has been measured at the n_TOF facility at CERN with a BaF2 total absorption calorimeter, in the energy range between 0.7 eV and 2.5 keV.

    Results: The Am243(n,γ) cross section has been successfully measured in the mentioned energy range. The resolved resonance region has been extended from 250 eV up to 400 eV. In the unresolved resonance region our results are compatible with one of the two incompatible capture data sets available below 2.5 keV. The data available in EXFOR and in the literature have been used to perform a simple analysis above 2.5 keV.

    Conclusions: The results of this measurement contribute to reduce the Am243(n,γ) cross section uncertainty and suggest that this cross section is underestimated up to 25% in the neutron energy range between 50 eV and a few keV in the present evaluated data libraries.

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    • Received 23 May 2014
    • Revised 1 July 2014

    DOI:https://doi.org/10.1103/PhysRevC.90.034608

    ©2014 American Physical Society

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    Vol. 90, Iss. 3 — September 2014

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    Images

    • Figure 1
      Figure 1

      Schematic view of the n_TOF total absorption calorimeter.

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    • Figure 2
      Figure 2

      Deposited energy spectrum of the Am243(n,γ) measurement together with different background contributions, without any condition on mcr. The top and bottom panels show the cases when pile-up corrections are neglected (a) and properly applied (b) in the calculation of the backgrounds, respectively. The effect is highlighted on a linear scale in the insets. The data correspond to neutron energies between 1 and 10 eV.

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    • Figure 3
      Figure 3

      Number of events detected in the Am243(n,γ) measurement as a function of the neutron energy, together with different background contributions and under the conditions of mcr>2 and 2.5<Esum<6 MeV.

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    • Figure 4
      Figure 4

      Experimental (solid lines) and simulated (dotted lines) deposited energy spectra from Am243 capture cascades for different multiplicities. On the left (a)–(e), the total γ-ray energy deposited in the TAC (Esum). On the right (f)–(j), the individual crystal energy spectra obtained by gating on the total γ-ray energy in the 4<Esum<6 MeV region. The spectra have been obtained from the strongest Am243 resonance at 1.35 eV. The oscillations present in some spectra at low energies are related with the background subtraction.

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    • Figure 5
      Figure 5

      Experimental (solid lines) and simulated (dotted lines) deposited energy spectra due to the detection of the sample activity. A sample mass of 6.77 mg of Am243 has been used.

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    • Figure 6
      Figure 6

      Normalization factors obtained in 18 different fits with sammy . In all cases, the initial thickness of the Am243 sample considered was 2×105 atoms/barn, which corresponds to a mass of 6.34 mg.

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    • Figure 7
      Figure 7

      Examples of the fitted n_TOF capture yield, in different energy ranges. The dashed line corresponds to the overall background considered in sammy .

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    • Figure 8
      Figure 8

      Ratio between the n_TOF capture cross section and three evaluations integrated over different energy intervals, ∫E1E2σγ,n_TOF(E)dE/∫E1E2σγ,eval(E)dE. The low energy limit of the first bin is 3 eV, in order to avoid the strongest resonance at 1.35 eV.

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    • Figure 9
      Figure 9

      Estimation of the number of missing resonances, performed in the 0–40 eV energy range. The experimental points were fitted to Eq. (2).

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    • Figure 10
      Figure 10

      Linear fit of ∑λgΓn,λ0 as a function of the neutron energy.

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    • Figure 11
      Figure 11

      Fitted n_TOF capture data in the URR together with the two different data sets provided by Weston et al., in their common energy range, and with the cross sections provided by the ENDF/B-VII.1 and JEFF-3.2 evaluations.

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    • Figure 12
      Figure 12

      Ratio between the n_TOF fitted capture cross section and the ones available in different evaluations. JEFF-3.2 is the same as JEFF-3.1, JENDL-3.3, and CENDL-3.1, in this energy range.

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    • Figure 13
      Figure 13

      PROFIL-1 neutron flux multiplied by the Am243 capture cross section in the JEFF-3.2 library.

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