Preequilibrium Asymmetries in the 
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 Prompt Fission Neutron Spectrum

Kelly, K. J.; Kawano, Toshihiko; O’Donnell, J. M.; Gomez, J. A.; Devlin, M.; Neudecker, Denise; Talou, P.; Lovell, A. E.; White, Morgan Curtis; Haight, R. C.; Taddeucci, T.N.; Mosby, S.; Lee, Hye Young; Wu, C. Y.; Henderson, R.; Henderson, J.; Buckner, Matthew

doi:10.1103/physrevlett.122.072503

Cited by 27 publications

(13 citation statements)

References 36 publications

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“…It was suggested in Ref. (18) that this feature is the pre-equilibrium component of the PFNS as it appears to match predictions of this PFNS component given in Refs. (34; 35; 36; 37).…”

Section: Comparison Of Experimental Resultssupporting

confidence: 76%

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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“…It was suggested in Ref. (18) that this feature is the pre-equilibrium component of the PFNS as it appears to match predictions of this PFNS component given in Refs. (34; 35; 36; 37).…”

Section: Comparison Of Experimental Resultssupporting

confidence: 76%

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

Self Cite

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“…These results were described in Ref. [11], where it was also shown that these counts appear to have an angular distribution consistent with a pure inelastic scattering reaction, providing experimental support to the theory that there is little-to-no cor- Figure 3. Third-chance fission and pre-equilibrium PFNS features observed by the Chi-Nu experiment for neutron-induced fission of 235 U (left) and 239 Pu (right) are shown here.…”

Section: Multi-chance and Pre-equilibrium Pfns Featuressupporting

confidence: 71%

“…1 of Ref. [11]. The evolution of the PFNS with increasing incident neutron energy is the convolution of these various possible fission paths, each of which may produce different features in the measured neutron spectrum in coincidence with fission.…”

Section: Introductionmentioning

confidence: 94%

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

et al. 2020

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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.

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“…These newer results include a large fraction of the PFNS, for fast neutroninduced fission of both 235 U and 239 Pu. Pre-equilibrium neutron distributions in the fission of 239 Pu have been reported previously [22], and these features as well as other features in the PFNS for incoming neutron energies above 5 MeV are reported elsewhere in this volume [23].…”

Section: Introductionmentioning

confidence: 70%

Prompt Fission Neutron Spectra for Neutron-Induced Fission of ²³⁹Pu and ²³⁵U

et al. 2020

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We report the current results of a large effort to accurately measure the Prompt Fission Neutron Spectra (PFNS) for neutron-induced fission of 235U and 239Pu for incident neutrons with energies from 1 to 20 MeV. The Chi-Nu experiment at the Los Alamos Neutron Science Center used an unmoderated, white spectrum of neutrons to induce fission in actinide samples that were placed inside a parallel plate avalanche counter to provide a fast fission signal. A double time-of-flight technique was used to determine the incoming and outgoing neutron energies. Two neutron detector arrays, one with 54 liquid scintillators and another with 22 lithium glass detectors, were used to detect the outgoing neutrons and measure the PFNS distributions over a wide range in outgoing neutron energy, from below 100 keV to 10 MeV. Extensive Monte Carlo modeling was used to understand the experiment response and extract the PFNS. Systematic errors and uncertainties in the method have been examined and quantified. A summary of these results for incoming energies from 1 to 5 MeV is presented here.

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Preequilibrium Asymmetries in the Pu239(n,f) Prompt Fission Neutron Spectrum

Cited by 27 publications

References 36 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

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

Prompt Fission Neutron Spectra for Neutron-Induced Fission of ²³⁹Pu and ²³⁵U

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Preequilibrium Asymmetries in the Pu239(n,f) Prompt Fission Neutron Spectrum

Cited by 27 publications

References 36 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

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

Prompt Fission Neutron Spectra for Neutron-Induced Fission of 239Pu and 235U

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Product

Resources

About

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

Prompt Fission Neutron Spectra for Neutron-Induced Fission of ²³⁹Pu and ²³⁵U