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Request ID15 Type of the request High Priority request
TargetReaction and processIncident EnergySecondary energy or angleTarget uncertaintyCovariance
 95-AM-241 (n,g),(n,tot) SIG  Thermal-Fast  See details 
FieldSubfieldDate Request createdDate Request acceptedOngoing action
 Fission LWR, Thermal 08-NOV-07 10-SEP-08 Y

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Requester: Dr Osamu IWAMOTO at JAEA, JPN

Project (context): JENDL and WPEC subgroup 26

The thermal value for the total cross section is inconsistent with the best value for the capture cross section. This inconsistency should be removed (JENDL). Current inconsistencies in the measured total cross section for the main low energy resonances should be removed and a capture measurement should be made to demonstrate consistency.

Design phases of selected reactor and fuel cycle concepts require improved data and methods in order to reduce margins for both economical and safety reasons. A first indicative nuclear data target accuracy assessment was made within WPEC Subgroup 26 (SG-26). The assessment indicated a list of nuclear data priorities for each of the systems considered (ABTR, SFR, EPR, GFR, LFR, ADMAB, VHTR, EPR). These nuclear data priorities should all be addressed to meet target accuracy requirements for the integral parameters characterizing those systems (see the accompanying requests originating from SG-26).

For JENDL: A new measurement with a total uncertainty of 5% for the thermal total cross section would be required to resolve the issue.
For SG-26: Target accuracies are specified per system and per energy group when they are not met by the BOLNA estimate of the current (initial) uncertainties.

Energy RangeUncertainty (%)
  InitialGFR ADMAB
67.4 -183 keV 7 4 2
24.8 -67.4 keV 8 3 2
9.12 -24.8 keV 7 3 2
2.03 -9.12 keV 7 3 2
0.454-2.03 keV 7 3 3

Justification document:
[1] Toru YAMAMOTO, "Analysis of Core Physics Experiments of High Moderation Full MOX LWR", Proc. of the 2005 Symposium on Nuclear Data, February 2-3, 2006, JAEA, Tokai, Japan, pp.7-13, JAEA-Conf 2006-009 (2006). (See attached document)
OECD/NEA WPEC Subgroup 26 Final Report: "Uncertainty and Target Accuracy Assessment for Innovative Systems Using Recent Covariance Data Evaluations" (Link to WPEC Subgroup 26 Report in PDF format, 6 Mb).

Comment from requester:
Given the present state of knowledge the above target accuracies are very tight. However, any attempt that significantly contributes to reducing the present accuracy for this quantity is strongly encouraged. Any such attempt will significantly enhance the accuracy with which reactor integral parameters may be estimated and will therefore impact economic and safety margins.

Additional file attached: Yamamoto_T(MOX-LWR)2006.pdf

Review comment:
New experimental work is ongoing at IRMM in collaboration with CEA. Recent capture measurements have taken place at Los Alamos. There appear to be no large discrepancies in thermal capture measurements dating from 2000 as long as it is clearly distinguished whether the isomer contribution is included or not. Sample material available at IRMM is not compatible with an accurate measurement of the total cross section at thermal energy.

Entry Status:
Work in progress (as of SG-C review of May 2018)

Main recent references:
Please report any missing information to


  • S. Nakamura et al., Thermal-Neutron Capture Cross Section and Resonance Integral of Americium-241, JNST 44 (2007) 1500, EXFOR 22998
  • M. Jandel et al., Neutron capture cross section of 241Am, PRC 78 (2008) 034609, EXFOR 14209
  • C. Lampoudis et al., Neutron transmission and capture cross section measurements for 241Am at the GELINA facility, Eur. Phys. J. Plus (2013) 128:86, EXFOR 23139
  • K. Fraval et al., Measurement and analysis of the 241Am(n,g) cross section with liquid scintillator detectors using time-of-flight spectroscopy at the n_TOF facility at CERN, PRC 89 (2014) 044609, EXFOR 23237
  • H. Harada et al., Capture Cross-section Measurement of 241Am(n,g) at J-PARC/MLF/ANNRI, NDS 119 (2014) 61, EXFOR 23172
  • K. Terada et al., Measurements of gamma-ray emission probabilities of 241,243Am and 239Np, JNST 53 (2016) 1881
  • K. Hirose et al., Simultaneous measurement of neutron-induced fission and capture cross sections for 241Am at neutron energies below fission threshold, NIM A 856 (2017) 133, EXFOR 23338
  • K. Terada et al., Measurements of neutron total and capture cross sections of 241Am with ANNRI at J-PARC (tentative title), to be submitted to JNST
  • E. Mendoza et al., Measurement and analysis of the 241Am neutron capture cross section at the n_TOF facility at CERN, PRC 97 (2018) 054616
  • New capture measurement performed in 2017 at n_TOF EAR2


  • G. Noguere et al., Partial-wave analysis of n+Am-241 reaction cross sections in the resonance region, PRC 92 (2015) 014607
  • K. Mizuyama et al., Correction of the thermal neutron capture cross section of 241Am obtained by the Westcott convention, JNST 54 (2017) 74
  • H. Harada, Improving nuclear data accuracy of Am-241 and Np-237 capture cross-sections, International Evaluation Cooperation, NEA/WPEC-41, see also G. Zerovnik et al., EPJ Conferences 146 (2017) 11035