The Covariance of PFNS Results from the Chi-Nu Experiment

Kelly, Keegan John; O’Donnell, John M.; Devlin, Matthew

doi:10.1051/epjconf/202328100026

Title: The Covariance of PFNS Results from the Chi-Nu Experiment

Journal Article · Wed Mar 29 00:00:00 EDT 2023 · EPJ Web of Conferences (Online)

DOI:https://doi.org/10.1051/epjconf/202328100026· OSTI ID:1969243

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Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

The prompt fission neutron spectrum (PFNS) from neutron-induced fission is a fundamental quantity for the behavior of nuclear reactors, and has been measured many times on a wide variety of nuclei and covering different ranges of incident and emitted neutron energies. However, results from past measurements are frequently called into question in modern nuclear data evaluations because of a lack of thorough experimental documentation and incomplete uncertainty analyses. The Chi-Nu experiment at Los Alamos National Laboratory was designed to produce high-precision measurements of the PFNS of major actinides over a wide range of incident and emitted neutron energies, and with the documentation and covariance analysis required to ensure that the results of this experiment maintain their impact long into the future, thereby avoiding this pitfall of past measurements. In this work we describe the Chi-Nu experiment along with summaries of the treatment of and methods developed to address two important components of the analysis of Chi-Nu data: random-coincidence backgrounds and MCNP simulations. Furthermore, we describe the first results for correlations not just between all data points collected on a single target nucleus, but also between all data points from separate Chi-Nu measurements on ²³⁵U and ²³⁹Pu. These correlations are important for accurately calculating ratios of the PFNS from one actinide to another, which are rare and can be informative for nuclear data evaluation efforts.

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Research Organization:: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA)

Grant/Contract Number:: 89233218CNA000001

OSTI ID:: 1969243

Report Number(s):: LA-UR-22-31615; TRN: US2313392

Journal Information:: EPJ Web of Conferences (Online), Vol. 281; ISSN 2100-014X

Publisher:: EDP SciencesCopyright Statement

Country of Publication:: United States

Language:: English

References (12)

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Numerical integration of detector response functions via Monte Carlo simulations Kelly, K. J.; O’Donnell, J. M.; Gomez, J. A. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 866 https://doi.org/10.1016/j.nima.2017.05.048	journal	September 2017
The Need for Precise and Well-documented Experimental Data on Prompt Fission Neutron Spectra from Neutron-induced Fission of 239Pu Neudecker, D.; Taddeucci, T. N.; Haight, R. C. Nuclear Data Sheets, Vol. 131 https://doi.org/10.1016/j.nds.2015.12.005	journal	January 2016
The impact of detection rate changes and correlations on random-coincidence background measurements Kelly, K. J.; O’Donnell, J. M.; Gomez, J. A. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 1045 https://doi.org/10.1016/j.nima.2022.167531	journal	January 2023
Utilization of MCNP®6 implicit-capture simulations for quantification of systematic uncertainties from experimental environments Kelly, K. J.; Gomez, J. A.; O’Donnell, J. M. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 954 https://doi.org/10.1016/j.nima.2018.10.089	journal	February 2020
Multiple-scattering Corrections to Measurements of the Prompt Fission Neutron Spectrum Taddeucci, T. N.; Haight, R. C.; Lee, H. Y. Nuclear Data Sheets, Vol. 123 https://doi.org/10.1016/j.nds.2014.12.024	journal	January 2015
Measurement of the U235(n,f) prompt fission neutron spectrum from 10 keV to 10 MeV induced by neutrons of energy from 1 MeV to 20 MeV Kelly, K. J.; Gomez, J. A.; Devlin, M. Physical Review C, Vol. 105, Issue 4 https://doi.org/10.1103/PhysRevC.105.044615	journal	April 2022
The Prompt Fission Neutron Spectrum of 235 U( n , f ) below 2.5 MeV for Incident Neutrons from 0.7 to 20 MeV Devlin, M.; Gomez, J. A.; Kelly, K. J. Nuclear Data Sheets, Vol. 148 https://doi.org/10.1016/j.nds.2018.02.008	journal	February 2018
Measurement of the ${}^{239}{Pu} (n, f)$ prompt fission neutron spectrum from 10 keV to 10 MeV induced by neutrons of energy 1–20 MeV Kelly, K. J.; Devlin, M.; O'Donnell, J. M. Physical Review C, Vol. 102, Issue 3 https://doi.org/10.1103/PhysRevC.102.034615	journal	September 2020
A new method to reduce the statistical and systematic uncertainty of chance coincidence backgrounds measured with waveform digitizers O׳Donnell, J. M. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 805 https://doi.org/10.1016/j.nima.2015.07.044	journal	January 2016
Preequilibrium Asymmetries in the ${}^{239}{Pu} (n, f)$ Prompt Fission Neutron Spectrum Kelly, K. J.; Kawano, T.; O’Donnell, J. M. Physical Review Letters, Vol. 122, Issue 7 https://doi.org/10.1103/PhysRevLett.122.072503	journal	February 2019
A multiple parallel-plate avalanche counter for fission-fragment detection Wu, C. Y.; Henderson, R. A.; Haight, R. C. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 794 https://doi.org/10.1016/j.nima.2015.05.010	journal	September 2015

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