93-Np-237(n,f)

Requester

Dr Fredrik TOVESSON at LANL, USA

Project (context)

Los Alamos National Laboratory

Impact

• 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.

Accuracy

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]).

References:

• [1] G. Aliberti et al., Annals of Nuclear Energy 33 (2006) 700-733.
• [2] M. Salvatores et al., Nuclear Science NEA/WPEC-26, www.oecd.org.
• [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

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 hprlinfo@oecd-nea.org

Experiments

• O. Shcherbakov et al., Neutron-Induced Fission of 233U, 238U, 232Th, 239Pu, 237Np, natPb and 209Bi Relative to 235U in the Energy Range 1-200 MeV, Jour. of Nuclear Science and Technology Suppl. 2 (2002) 230, EXFOR 41455
• F. Tovesson and T. Hill, Neutron induced fission cross section of 237Np from 100 keV to 200 MeV, PRC 75 (2007) 034610, EXFOR 14130
• M.S. Basunia, The (3He, t f) as a surrogate reaction to determine (n,f) cross sections in the 10-20 MeV energy range, NIM B 267 (2009) 1899, EXFOR 31673
• C. Paradela, et al., Neutron-induced fission cross section of 234U and 237Np measured at the CERN Neutron Time-of-Flight (n_TOF) facility, PRC 82 (2010) 034601, EXFOR 23126
• M. Diakaki et al., Determination of the 237Np(n,f) reaction cross section for En = 4.5-5.3 MeV using a MicroMegas detector assembly, EPJA 49 (2013) 62, EXFOR 23189
• M. Diakaki et al., Neutron-induced fission cross section of 237Np in the keV to MeV range at the CERN n_TOF facility, PRC 93 (2016) 034614, EXFOR 22742
• L. Tassan-Got et al., Fission program at n_TOF, EPJ Web of Conferences 211, 03006 (2019)

Theory/Evaluation

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

Validation

• G. Palmiotti, et al., Combined Use of Integral Experiments and Covariance Data, Nuclear Data Sheets 118 (2014) 596