Unrecognized Sources of Uncertainties (USU) in Experimental Nuclear Data

Capote, R.; Badikov, Sergey; Carlson, A.D.; Durán, I.; Gunsing, F.; Neudecker, Denise; Pronyaev, V.G.; Schillebeeckx, P.; Schnabel, Georg; Smith, Donald L.; Wallner, A.

doi:10.1016/j.nds.2019.12.004

Cited by 34 publications

(29 citation statements)

References 74 publications

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“…The agreement of the results in Figs. 12-16 is also consistent with the possible presence of one or more unidentified sources of error in the acquired data common between these correlated experiments, generally termed unrecognized sources of uncertainties (USU) (38), though such issues are difficult to identify by definition.…”

Section: Comparison Of Experimental Resultsmentioning

confidence: 52%

Comparison of Results from Recent NNSA and CEA Measurements of the 239Pu(n, f) Prompt Fission Neutron Spectrum

Kelly

Marini

Taïeb

et al. 2021

Nuclear Data Sheets

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The National Nuclear Security Administration (NNSA)/DP French Alternative Energies and Atomic Energy Commission (CEA)/DAM agreement on cooperation on fundamental science is a U.S.-French collaborative effort to combine intellectual and experimental resources and further the relevant nuclear science. Recently, both the NNSA and CEA experimental teams performed high-statistics measurements of the 239 Pu(n,f ) prompt fission neutron spectrum (PFNS) at the Los Alamos Neutron Science Center, both of which were recently published in the journal Physical Review C. These separate measurements used the same experimental area and a common neutron detector array, but differ in many aspects including background assessments, data acquisition systems and philosophies, fission detectors, and PFNS extraction techniques. Hence, some aspects of the experimental methods and associated uncertainties are highly correlated while others are independent. The results from both measurements broke new ground for PFNS measurements given their higher accuracy and more detailed study of corrections necessary for the measured quantity compared to existing literature measurements, and both will significantly impact PFNS nuclear data evaluations for the foreseeable future. The focus of this work is to document a comparison of the results from these distinct measurements in terms of the acquired data, the PFNS results, and the measured average PFNS energies. While systematic differences between the PFNS results are present on the 1-3% level, the acquired data relative to each respective measurement at low incident neutron energies are in remarkable agreement, as are the conclusions regarding the magnitude and position of features in the PFNS relating to second-chance fission, third-chance fission, and pre-equilibrium neutron emission.

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Section: Comparison Of Experimental Resultsmentioning

confidence: 52%

Comparison of Results from Recent NNSA and CEA Measurements of the 239Pu(n, f) Prompt Fission Neutron Spectrum

Kelly

Marini

Taïeb

et al. 2021

Nuclear Data Sheets

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“…It will be explained in Section 4.3 that while the same input information is used for both studies, that some aspects of the PUBs formalism to obtain total bounds differ from how the evaluated covariances are obtained with GMA. Hence, PUBs indicating that ENDF/B-VII.1 239 Pu(n,f) cross-section uncertainties are underestimated is not only well-supported by USU studies [15,18,19], but also by looking explicitly at the covariance input for the evaluation.…”

Section: Resultsmentioning

confidence: 73%

“…This uncertainty would also be missing in the current PUBs estimate. The USU technique described in reference [15,18,19] might be able to capture this uncertainty if it leads to a spread across all measured data of about the size of the uncorrected effect. If this missing effect leads to an equal off-set in all data-sets, the USU technique will not capture it.…”

Section: Resultsmentioning

confidence: 99%

“…The original GMA output for the current NDS version provided similar evaluated uncertainties to the previous one as these concerns could not be addressed within GMA in a timely manner. However, an additional uncertainty component, namely the "unrecognized source of uncertainty" (USU) one estimated by a method proposed by Gai [15,18,19], was added in quadrature to the GMA evaluated uncertainties. These increased uncertainties were then released as part of the current NDS data and covariances.…”

Section: Pu(nf) Cross Sections Released By the Neutron Data Stanmentioning

confidence: 99%

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Validating nuclear data uncertainties obtained from a statistical analysis of experimental data with the “Physical Uncertainty Bounds” method

Neudecker

White

Vaughan

et al. 2020

EPJ Nuclear Sci. Technol.

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Concerns within the nuclear data community led to substantial increases of Neutron Data Standards (NDS) uncertainties from its previous to the current version. For example, those associated with the NDS reference cross section 239Pu(n,f) increased from 0.6–1.6% to 1.3–1.7% from 0.1–20 MeV. These cross sections, among others, were adopted, e.g., by ENDF/B-VII.1 (previous NDS) and ENDF/B-VIII.0 (current NDS). There has been a strong desire to be able to validate these increases based on objective criteria given their impact on our understanding of various application uncertainties. Here, the “Physical Uncertainty Bounds” method (PUBs) by Vaughan et al. is applied to validate evaluated uncertainties obtained by a statistical analysis of experimental data. We investigate with PUBs whether ENDF/B-VII.1 or ENDF/B-VIII.0 239Pu(n,f) cross-section uncertainties are more realistic given the information content used for the actual evaluation. It is shown that the associated conservative (1.5–1.8%) and minimal realistic (1.1–1.3%) uncertainty bounds obtained by PUBs enclose ENDF/B-VIII.0 uncertainties and indicate that ENDF/B-VII.1 uncertainties are underestimated.

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“…The work focused on helping evaluators in identifying missing or suspiciously low uncertainties and missing correlations between uncertainties of the same and different experiments when estimating covariances for measurements entering their evaluations. Also work [3] has been done on unrecognized sources of uncertainties in experimental nuclear data. Inconsistencies in data have led to the speculation that for many (if not all) experiments of a given type there exist signicant unrecognized (unknown) experimentally related sources of uncertainty that cannot be eliminated by repeated measurements using the same analysis.…”

Section: Introductionmentioning

confidence: 99%

Work on the neutron standards since the completion of the standards evaluation

Carlson

2020

EPJ Web Conf.

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An evaluation of the neutron standards that included the neutron cross section standards was recently completed. It is important to maintain experimental programs to increase the quality and extend the database for the neutron cross section standards in order to improve evaluations of them. In this paper work will be reported on new or continuing efforts on the cross section standards including that on the 30 keV Maxwellian averaged cross section for the 197Au(n,γ) reaction that is now a standard and is used in neutron capture cross section measurements as a standard for reactions important for astrophysics.

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Unrecognized Sources of Uncertainties (USU) in Experimental Nuclear Data

Cited by 34 publications

References 74 publications

Comparison of Results from Recent NNSA and CEA Measurements of the 239Pu(n, f) Prompt Fission Neutron Spectrum

Comparison of Results from Recent NNSA and CEA Measurements of the 239Pu(n, f) Prompt Fission Neutron Spectrum

Validating nuclear data uncertainties obtained from a statistical analysis of experimental data with the “Physical Uncertainty Bounds” method

Work on the neutron standards since the completion of the standards evaluation

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