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Request ID44 Type of the request High Priority request
TargetReaction and processIncident EnergySecondary energy or angleTarget uncertaintyCovariance
 93-NP-237 (n,f) SIG,DE  200 keV-20 MeV  2-3 Y
FieldSubfieldCreated dateAccepted dateOngoing actionArchived Date
 Fission fast reactors 11-MAY-15 18-MAY-15 16-MAY-18

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Requester: Dr Fredrik TOVESSON at LANL, USA

Project (context): Los Alamos National Laboratory


  • The Np-237 fission cross section has impact for certain fast nuclear reactor designs. A sensitivity study by Aliberti et al. [1] pointed to a target accuracy of 8% for this cross section for Sodium-cooled Fast Reactor of the Gen-IV type (high level waste recycling).
  • WPEC Subgroup-26 [2]: Present uncertainty (BOLNA) 6-8% from 0.5-6 MeV. Required uncertainty for an Accelerator Driven Minor Actinide Burner (ADMAB): 1.5-4 %.
  • For many measurements the 237Np(n,f) is a reference cross section that is valuable on account of its low fission threshold and moderate activity.

Uncertainties of 2-3%

Justification document:
There is a discrepancy of about 6-9% between a recent measurement performed by the n_TOF collaboration and ENDF/B-VII (C. Paradela et al. [3]).
The higher n_TOF values are supported by a validation exercise by Leong et al. [4].
A recent independent result in the energy range from 4.8 to 5.6 MeV yields cross sections that in function of energy first agree with ENDF/B-VII and then with the n_TOF result (M. Diakaki et al. [5]).
Independently an issue was recently found when cross sections for Pu-isotopes referred to the 238U(n,f) cross section were compared to the same cross sections referred to the 237Np(n,f) cross section in the same measurement arrangement (P. Salvador et al. [6]).

Comment from requester:

The request is well motivated and of some concern also to reactor dosimetry when using spectral indices and/or reaction rates of 237Np fission chambers (IRDFF [7]).

  • [1] G. Aliberti et al., Annals of Nuclear Energy 33 (2006) 700-733.
  • [2] M. Salvatores et al., Nuclear Science NEA/WPEC-26,
  • [3] C. Paradela et al., Phys. Rev. C 82 (2010) 034601; Korean Physical Society 59 (2011) 1519.
  • [4] L.S. Leong et al., Annals of Nuclear Energy 54 (2013) 36

Additional file attached: 1-s2.0-S0306454906000296-main.pdf

Review comment:

Entry Status:
Completed (as of SG-C review of May 2018) - The request was related to a discrepancy between measurements performed at LANSCE [Tovesson:2007] and n_TOF [Paradela:2010]. New measurements using improved PPAC detectors have shown that the overestimation of the n_TOF data was caused by different roughness of the surface of the Np and U samples [Tassan-Got:2019].

Main recent references:
Please report any missing information to



  • M.B. Chadwick et al., ENDF/B-VII.0: Next Generation Evaluated Nuclear Data Library for Nuclear Science and Technology, NDS 107 (2006) 2931


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