scholarly journals Systematic Distortion Factor and Unrecognized Source of Uncertainties in Nuclear Data Measurements and Evaluations

Metrology ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 1-18
Author(s):  
Nikolay V. Kornilov ◽  
Vladimir G. Pronyaev ◽  
Steven M. Grimes
Keyword(s):  
Cross Sections ◽  
Nuclear Data ◽  
Fission Neutron ◽  
Model Case ◽  
Distortion Factor ◽  
True Value ◽  
New Information ◽  
Measurement Results ◽  
Prompt Fission ◽  
Prompt Fission Neutron

Each experiment provides new information about the value of some physical quantity. However, not only measured values but also the uncertainties assigned to them are an important part of the results. The metrological guides provide recommendations for the presentation of the uncertainties of the measurement results: statistics and systematic components of the uncertainties should be explained, estimated, and presented separately as the results of the measurements. The experimental set-ups, the models of experiments for the derivation of physical values from primary measured quantities, are the product of human activity, making it a rather subjective field. The Systematic Distortion Factor (SDF) may exist in any experiment. It leads to the bias of the measured value from an unknown “true” value. The SDF appears as a real physical effect if it is not removed with additional measurements or analysis. For a set of measured data with the best evaluated true value, their differences beyond their uncertainties can be explained by the presence of Unrecognized Source of Uncertainties (USU) in these data. We can link the presence of USU in the data with the presence of SDF in the results of measurements. The paper demonstrates the existence of SDF in Prompt Fission Neutron Spectra (PFNS) measurements, measurements of fission cross sections, and measurements of Maxwellian spectrum averaged neutron capture cross sections for astrophysical applications. The paper discusses introducing and accounting for the USU in the data evaluation in cases when SDF cannot be eliminated. As an example, the model case of 238U(n,f)/235U(n,f) cross section ratio evaluation is demonstrated.

Measurement of Selected Differential Cross Sections in 235U Spectrum

2019 ◽  
Vol 5 (3) ◽  
Author(s):  
Nicola Burianová ◽  
Michal Košt´ál ◽  
Martin Schulc ◽  
Jan Šimon ◽  
Martin Mareček ◽  
...  
Keyword(s):  
Cross Sections ◽  
Nuclear Data ◽  
Reaction Rates ◽  
Fission Neutron ◽  
Data Libraries ◽  
Nuclear Data Libraries ◽  
Prompt Fission Neutron Spectrum ◽  
Prompt Fission ◽  
Prompt Fission Neutron ◽  
Good Agreement

This paper describes the measurement of 55Mn(n,2n) and 127I(n,2n) reaction rates in a well-defined reactor field in a special core of LR-0 reactor. The reaction rates were derived using gamma-spectrometry by measuring gamma activities of irradiated MnO2 and NaI samples at a high purity germanium (HPGe) detector. The spectral average cross section (SACS) in 235U prompt fission neutron spectrum (PFNS) was experimentally determined to be 0.2393 ± 0.015 × 10−3 b for 55Mn and 1.2087 ± 0.052 × 10−3 b for 127I. These obtained results were compared with calculations by MCNP6 code using ENDF/B VII.1, ENDF/B VII, JEFF-3.1, JEFF-3.2, JENDL-3.3, JENDL-4, ROSFOND- 2010, CENDL-3.1, and IRDFF nuclear data libraries. In a case of 55Mn, a good agreement with ENDF/B VII.1, JEFF 3.1, JENDL 3.3, JENDL 4, ROSFOND, and CENDL 3.1 nuclear data libraries was found, where C/E−1 is 0.1%, while IRDFF underestimated by about 15.8%. In the case of 127I, more significant discrepancies were found, where JENDL 3.3 and JENDL 4 overestimate the result by about 31.3%.

scholarly journals Cross-observables and cross-isotopes correlations in nuclear data from integral constraints

2018 ◽  
Vol 4 ◽  
pp. 35 ◽  
Author(s):  
Eric Bauge ◽  
Dimitri A. Rochman
Keyword(s):  
Cross Sections ◽  
Nuclear Data ◽  
Fission Neutron ◽  
Wide Range ◽  
Data Files ◽  
Fission Neutrons ◽  
Prompt Fission ◽  
Benchmark Evaluation ◽  
Prompt Fission Neutron ◽  
Good Agreement

Most recent evaluated nuclear data files exhibit excellent integral performance, as shown by the very good agreement between experimental and calculated keff values over a wide range of benchmark integral experiments. However, the propagation of the uncertainties associated with those nuclear data to integral observables, generally produces calculated distribution which are much (3–5 times) wider than the experimental uncertainties. Reducing the variances of the evaluated data to achieve consistency at the integral level would lead to unreasonably narrow variances in the light of differential experimental data. One way of solving that paradox could be to allow, for different observables like fission cross-sections (σf), the prompt fission neutron spectra (χ), and the average multiplicity of fission neutrons ([see formula in PDF]) to be correlated in a Bayesian-like, Total Monte-Carlo approach, under constraints from integral experiments from the ICSBEP (International International Criticality Safety Benchmark Evaluation Project) benchmark compilation. Future developments will be highlighted and restrictions imposed by the current formatting of nuclear data will be discussed.

scholarly journals Observations of poorly-known features of the 239Pu and 235U prompt fission neutron spectra

2020 ◽  
Vol 239 ◽  
pp. 05010
Author(s):  
Keegan J. Kelly ◽  
Jaime A. Gomez ◽  
John M. O'Donnell ◽  
Matthew Devlin ◽  
Robert C. Haight ◽  
...  
Keyword(s):  
Experimental Data ◽  
Neutron Spectrum ◽  
Neutron Emission ◽  
National Laboratory ◽  
Nuclear Data ◽  
Fission Neutron ◽  
Fission Neutron Spectrum ◽  
Wide Range ◽  
Prompt Fission ◽  
Prompt Fission Neutron

Prompt fission neutron spectrum (PFNS) evaluations use provide nuclear data for the PFNS across a wide range of incident and outgoing neutron energies. However, experimental data underlying the evaluation are sparse, inconsistent, and incomplete with respect to the desired incident and outgoing energy coverage. As such, evaluations sometimes predict features of the PFNS, such those relating to multi-chance fission and pre-equilibrium pre-fission neutron emission, without any experimental validation. The Chi-Nu experiment at Los Alamos National Laboratory has recently obtained high-precision results for the 239Pu and 235U PFNS which, for the first time in both cases, have shed light on multi-chance fission and pre-equilibrium contributions to the observed fission neutron spectrum. In addition to providing the first experimental data on some of these fission properties, the angular coverage of the Chi-Nu experiment allows for the extraction of angular distributions of pre-equilibrium pre-fission neutrons. PFNS results of multi-chance fission and pre-equilibrium pre-fission neutron emission are discussed in this proceedings in terms of the observed neutron spectrum and the average PFNS energies.

scholarly journals ARIADNE – a program estimating covariances in detail for neutron experiments

2018 ◽  
Vol 4 ◽  
pp. 34 ◽  
Author(s):  
Denise Neudecker
Keyword(s):  
Experimental Data ◽  
Uncertainty Quantification ◽  
Nuclear Data ◽  
Fission Neutron ◽  
Efficient Manner ◽  
Plain Text ◽  
Uncertainty Sources ◽  
Evaluation Community ◽  
Prompt Fission ◽  
Prompt Fission Neutron

The python program ARIADNE is a tool developed for evaluators to estimate detailed uncertainties and covariances for experimental data in a consistent and efficient manner. Currently, it is designed to aid in the uncertainty quantification of prompt fission neutron spectra, and was employed to estimate experimental covariances for CIELO and ENDF/B-VIII.0 evaluations. It provides a streamlined way to estimate detailed covariances by (1) implementing uncertainty quantification algorithms specific to the observables, (2) defining input quantities for typically encountered uncertainty sources and correlation shapes, and (3) automatically generating plots of data, uncertainties and correlations, GND formatted XML and plain text output files. Covariances of the same and between different datasets can be estimated, and tools are provided to assemble a database of experimental data and covariances for an evaluation based on ARIADNE outputs. The underlying IPython notebook files can be easily stored, including all assumptions on uncertainties, leading to more reproducible inputs for nuclear data evaluations. Here, the key inputs and outputs are shown along with a representative example for the current version of ARIADNE to illustrate its usability and to open a discussion on how it could address further needs of the nuclear data evaluation community.

scholarly journals Fission cross-sections, prompt fission neutron and γ-ray emission in request for nuclear applications

2016 ◽  
Vol 122 ◽  
pp. 01005
Author(s):  
F.-J. Hambsch ◽  
P. Salvador-Castiñeira ◽  
S. Oberstedt ◽  
A. Göök ◽  
R. Billnert
Keyword(s):  
Cross Sections ◽  
Fission Neutron ◽  
Γ Ray ◽  
Prompt Fission ◽  
Prompt Fission Neutron ◽  
Nuclear Applications

scholarly journals Prompt fission neutron emission in the reaction 235U(n,f)

2018 ◽  
Vol 169 ◽  
pp. 00004 ◽  
Author(s):  
Alf Göök ◽  
Franz-Josef Hambsch ◽  
Stephan Oberstedt
Keyword(s):  
Fission Fragment ◽  
Ionization Chamber ◽  
Neutron Emission ◽  
Nuclear Data ◽  
Fission Neutron ◽  
Fission Fragments ◽  
Position Sensitive ◽  
Prompt Fission ◽  
Prompt Fission Neutron ◽  
Reaction 235U

Experimental activities at JRC-Geel on prompt fission neutron (PFN) emission in response to OECD/NEA nuclear data requests are presented in this contribution. Specifically, on-going investigations of PFN emission from the reaction 235U(n,f) in the region of the resolved resonances, taking place at the GELINA facility, are presented. The focus of this contribution lies on studies of PFN correlations with fission fragment properties. The experiment employs a scintillation detector array for neutron detection, while fission fragment properties are determined via the double kinetic energy technique using a position sensitive twin ionization chamber. This setup allows us to study several correlations between properties of neutron and fission fragments simultaneously. Results on PFN correlations with fission fragment properties from the present study differ significantly from earlier studies on this reaction, induced by thermal neutrons.

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