The Experts below are selected from a list of 28374 Experts worldwide ranked by ideXlab platform
R C Haight - One of the best experts on this subject based on the ideXlab platform.
-
Prompt-Fission-Neutron spectra in the $^{239}\mathrm{Pu}(\mathit{n},\phantom{\rule{0.28em}{0ex}}\mathit{f})$ reaction
Phys.Rev.C, 2020Co-Authors: P. Marini, J A Gomez, M Devlin, J Taieb, B Laurent, G Belier, A. Chatillon, D. Etasse, P. Morfouace, R C HaightAbstract:Prompt-Fission-Neutron spectra from Pu239 (n,f) were measured with respect to Cf252 spontaneous Fission for incident Neutron energies from 0.7 to 700MeV at the Weapons Neutron Research facility (WNR) of the Los Alamos Neutron Science Center. A newly designed high-efficiency Fission chamber was coupled to the highly segmented Chi-Nu Neutron liquid scintillator array to detect Neutrons emitted in Fission events. The double time-of-flight technique was used to deduce the incident Neutron energies from the spallation target and the outgoing-Neutron energies from the Fission chamber. Prompt-Fission-Neutron spectra (PFNS) were measured with respect to Cf252 spontaneous Fission down to 200keV and up to about 12MeV for all the incident Neutron energies with typical total uncertainties well below 2% up to about 7-MeV outgoing-Neutron energy. The general trend of PFNS is well reproduced by JEFF3.3 and ENDF evaluations, although a better agreement is found with JEFF3.3. Discrepancies were observed for the low-energy part of the spectra, especially around the opening of the second-, third- and fourth-chance Fission. Neutron average kinetic energies as a function of incident Neutron energy are obtained experimentally with reported total uncertainties below 0.5%. The measured values agree with the most recent data. The trend is fairly well reproduced by the JEFF3.3 evaluation, although it fails to reproduce the experimental values within their uncertainties.
-
preequilibrium asymmetries in the 239 pu n f prompt Fission Neutron spectrum
Physical Review Letters, 2019Co-Authors: K J Kelly, J M Odonnell, J A Gomez, M Devlin, D Neudecker, Patrick Talou, M C White, A E Lovell, T. Kawano, R C HaightAbstract:: The physical properties of Neutrons emitted from Neutron-induced Fission are fundamental to our understanding of nuclear Fission. However, while state-of-the-art Fission models still incorporate isotropic Fission Neutron spectra, it is believed that the preequilibrium preFission component of these spectra is strongly anisotropic. The lack of experimental guidance on this feature has not motivated incorporation of anisotropic Neutron spectra in Fission models, though any significant anisotropy would impact descriptions of a Fissioning system. In the present work, an excess of counts at high energies in the Fission Neutron spectrum of ^{239}Pu is clearly observed and identified as an excess of the preequilibrium preFission distribution above the postFission Neutron spectrum. This excess is separated from the underlying postFission Neutron spectrum, and its angular distribution is determined as a function in incident Neutron energy and outgoing Neutron detection angle. Comparison with Neutron scattering models provides the first experimental evidence that the preequilibrium angular distribution is uncorrelated with the Fission axis. The results presented here also impact the interpretation of several influential prompt Fission Neutron spectrum measurements.
-
Preequilibrium Asymmetries in the ^{239}Pu(n,f) Prompt Fission Neutron Spectrum.
Physical Review Letters, 2019Co-Authors: K J Kelly, J A Gomez, M Devlin, D Neudecker, Patrick Talou, M C White, J. M. O'donnell, A E Lovell, T. Kawano, R C HaightAbstract:: The physical properties of Neutrons emitted from Neutron-induced Fission are fundamental to our understanding of nuclear Fission. However, while state-of-the-art Fission models still incorporate isotropic Fission Neutron spectra, it is believed that the preequilibrium preFission component of these spectra is strongly anisotropic. The lack of experimental guidance on this feature has not motivated incorporation of anisotropic Neutron spectra in Fission models, though any significant anisotropy would impact descriptions of a Fissioning system. In the present work, an excess of counts at high energies in the Fission Neutron spectrum of ^{239}Pu is clearly observed and identified as an excess of the preequilibrium preFission distribution above the postFission Neutron spectrum. This excess is separated from the underlying postFission Neutron spectrum, and its angular distribution is determined as a function in incident Neutron energy and outgoing Neutron detection angle. Comparison with Neutron scattering models provides the first experimental evidence that the preequilibrium angular distribution is uncorrelated with the Fission axis. The results presented here also impact the interpretation of several influential prompt Fission Neutron spectrum measurements.
-
the prompt Fission Neutron spectrum of 235 u n f below 2 5 mev for incident Neutrons from 0 7 to 20 mev
Nuclear Data Sheets, 2018Co-Authors: M Devlin, K J Kelly, J M Odonnell, J A Gomez, R C Haight, T.n. Taddeucci, B A Perdue, N. Fotiades, S Mosby, J L UllmannAbstract:Abstract New prompt Fission Neutron spectrum measurements are reported for 235U( n , f ) reactions induced by Neutrons with energies from 0.7 to 20 MeV. These measurements cover outgoing Neutron energies from 2.5 MeV down to 10 keV, using an array of 6Li-glass scintillators for Neutron detection and a double time-of-flight technique. The Neutrons were produced at the Weapons Neutron Research facility of the Los Alamos Neutron Science Center. A detailed MCNP® model of the experimental equipment and the surrounding room was used to interpret the experimental results. Backgrounds were measured in situ, making use of the time-dependent singles rates of the various detectors with asynchronous readout from waveform digitizers. The results presented here have been included in a re-evaluation of the Fission Neutron spectra for this Fissioning system, a description of which is presented elsewhere in this issue.
-
The 235 U prompt Fission Neutron spectrum measured by the Chi-Nu project at LANSCE
EPJ Web of Conferences, 2017Co-Authors: J A Gomez, K J Kelly, M Devlin, R C Haight, J. M. O'donnell, T.n. Taddeucci, Shea Mosby, Hye Young Lee, N. Fotiades, D NeudeckerAbstract:The Chi-Nu experiment aims to accurately measure the prompt Fission Neutron spectrum for the major actinides. At the Los Alamos Neutron Science Center (LANSCE), Fission can be induced with Neutrons ranging from 0.7 MeV and above. Using a two arm time-of-flight (TOF) technique, the Fission Neutrons are measured in one of two arrays: a 22-6 Li glass array for lower energies, or a 54-liquid scintillator array for outgoing energies of 0.5 MeV and greater. Presented here are the collaboration's preliminary efforts at measuring the 235 U PFNS.
M Devlin - One of the best experts on this subject based on the ideXlab platform.
-
Observations of poorly-known features of the 239Pu and 235U prompt Fission Neutron spectra
EPJ Web of Conferences, 2020Co-Authors: K J Kelly, J A Gomez, M Devlin, D Neudecker, J. M. O'donnell, Robert C. Haight, T.n. Taddeucci, Shea Mosby, Hye Young Lee, Toshihiko KawanoAbstract: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.
-
Prompt-Fission-Neutron spectra in the $^{239}\mathrm{Pu}(\mathit{n},\phantom{\rule{0.28em}{0ex}}\mathit{f})$ reaction
Phys.Rev.C, 2020Co-Authors: P. Marini, J A Gomez, M Devlin, J Taieb, B Laurent, G Belier, A. Chatillon, D. Etasse, P. Morfouace, R C HaightAbstract:Prompt-Fission-Neutron spectra from Pu239 (n,f) were measured with respect to Cf252 spontaneous Fission for incident Neutron energies from 0.7 to 700MeV at the Weapons Neutron Research facility (WNR) of the Los Alamos Neutron Science Center. A newly designed high-efficiency Fission chamber was coupled to the highly segmented Chi-Nu Neutron liquid scintillator array to detect Neutrons emitted in Fission events. The double time-of-flight technique was used to deduce the incident Neutron energies from the spallation target and the outgoing-Neutron energies from the Fission chamber. Prompt-Fission-Neutron spectra (PFNS) were measured with respect to Cf252 spontaneous Fission down to 200keV and up to about 12MeV for all the incident Neutron energies with typical total uncertainties well below 2% up to about 7-MeV outgoing-Neutron energy. The general trend of PFNS is well reproduced by JEFF3.3 and ENDF evaluations, although a better agreement is found with JEFF3.3. Discrepancies were observed for the low-energy part of the spectra, especially around the opening of the second-, third- and fourth-chance Fission. Neutron average kinetic energies as a function of incident Neutron energy are obtained experimentally with reported total uncertainties below 0.5%. The measured values agree with the most recent data. The trend is fairly well reproduced by the JEFF3.3 evaluation, although it fails to reproduce the experimental values within their uncertainties.
-
preequilibrium asymmetries in the 239 pu n f prompt Fission Neutron spectrum
Physical Review Letters, 2019Co-Authors: K J Kelly, J M Odonnell, J A Gomez, M Devlin, D Neudecker, Patrick Talou, M C White, A E Lovell, T. Kawano, R C HaightAbstract:: The physical properties of Neutrons emitted from Neutron-induced Fission are fundamental to our understanding of nuclear Fission. However, while state-of-the-art Fission models still incorporate isotropic Fission Neutron spectra, it is believed that the preequilibrium preFission component of these spectra is strongly anisotropic. The lack of experimental guidance on this feature has not motivated incorporation of anisotropic Neutron spectra in Fission models, though any significant anisotropy would impact descriptions of a Fissioning system. In the present work, an excess of counts at high energies in the Fission Neutron spectrum of ^{239}Pu is clearly observed and identified as an excess of the preequilibrium preFission distribution above the postFission Neutron spectrum. This excess is separated from the underlying postFission Neutron spectrum, and its angular distribution is determined as a function in incident Neutron energy and outgoing Neutron detection angle. Comparison with Neutron scattering models provides the first experimental evidence that the preequilibrium angular distribution is uncorrelated with the Fission axis. The results presented here also impact the interpretation of several influential prompt Fission Neutron spectrum measurements.
-
Preequilibrium Asymmetries in the ^{239}Pu(n,f) Prompt Fission Neutron Spectrum.
Physical Review Letters, 2019Co-Authors: K J Kelly, J A Gomez, M Devlin, D Neudecker, Patrick Talou, M C White, J. M. O'donnell, A E Lovell, T. Kawano, R C HaightAbstract:: The physical properties of Neutrons emitted from Neutron-induced Fission are fundamental to our understanding of nuclear Fission. However, while state-of-the-art Fission models still incorporate isotropic Fission Neutron spectra, it is believed that the preequilibrium preFission component of these spectra is strongly anisotropic. The lack of experimental guidance on this feature has not motivated incorporation of anisotropic Neutron spectra in Fission models, though any significant anisotropy would impact descriptions of a Fissioning system. In the present work, an excess of counts at high energies in the Fission Neutron spectrum of ^{239}Pu is clearly observed and identified as an excess of the preequilibrium preFission distribution above the postFission Neutron spectrum. This excess is separated from the underlying postFission Neutron spectrum, and its angular distribution is determined as a function in incident Neutron energy and outgoing Neutron detection angle. Comparison with Neutron scattering models provides the first experimental evidence that the preequilibrium angular distribution is uncorrelated with the Fission axis. The results presented here also impact the interpretation of several influential prompt Fission Neutron spectrum measurements.
-
the prompt Fission Neutron spectrum of 235 u n f below 2 5 mev for incident Neutrons from 0 7 to 20 mev
Nuclear Data Sheets, 2018Co-Authors: M Devlin, K J Kelly, J M Odonnell, J A Gomez, R C Haight, T.n. Taddeucci, B A Perdue, N. Fotiades, S Mosby, J L UllmannAbstract:Abstract New prompt Fission Neutron spectrum measurements are reported for 235U( n , f ) reactions induced by Neutrons with energies from 0.7 to 20 MeV. These measurements cover outgoing Neutron energies from 2.5 MeV down to 10 keV, using an array of 6Li-glass scintillators for Neutron detection and a double time-of-flight technique. The Neutrons were produced at the Weapons Neutron Research facility of the Los Alamos Neutron Science Center. A detailed MCNP® model of the experimental equipment and the surrounding room was used to interpret the experimental results. Backgrounds were measured in situ, making use of the time-dependent singles rates of the various detectors with asynchronous readout from waveform digitizers. The results presented here have been included in a re-evaluation of the Fission Neutron spectra for this Fissioning system, a description of which is presented elsewhere in this issue.
D Neudecker - One of the best experts on this subject based on the ideXlab platform.
-
Observations of poorly-known features of the 239Pu and 235U prompt Fission Neutron spectra
EPJ Web of Conferences, 2020Co-Authors: K J Kelly, J A Gomez, M Devlin, D Neudecker, J. M. O'donnell, Robert C. Haight, T.n. Taddeucci, Shea Mosby, Hye Young Lee, Toshihiko KawanoAbstract: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.
-
preequilibrium asymmetries in the 239 pu n f prompt Fission Neutron spectrum
Physical Review Letters, 2019Co-Authors: K J Kelly, J M Odonnell, J A Gomez, M Devlin, D Neudecker, Patrick Talou, M C White, A E Lovell, T. Kawano, R C HaightAbstract:: The physical properties of Neutrons emitted from Neutron-induced Fission are fundamental to our understanding of nuclear Fission. However, while state-of-the-art Fission models still incorporate isotropic Fission Neutron spectra, it is believed that the preequilibrium preFission component of these spectra is strongly anisotropic. The lack of experimental guidance on this feature has not motivated incorporation of anisotropic Neutron spectra in Fission models, though any significant anisotropy would impact descriptions of a Fissioning system. In the present work, an excess of counts at high energies in the Fission Neutron spectrum of ^{239}Pu is clearly observed and identified as an excess of the preequilibrium preFission distribution above the postFission Neutron spectrum. This excess is separated from the underlying postFission Neutron spectrum, and its angular distribution is determined as a function in incident Neutron energy and outgoing Neutron detection angle. Comparison with Neutron scattering models provides the first experimental evidence that the preequilibrium angular distribution is uncorrelated with the Fission axis. The results presented here also impact the interpretation of several influential prompt Fission Neutron spectrum measurements.
-
Preequilibrium Asymmetries in the ^{239}Pu(n,f) Prompt Fission Neutron Spectrum.
Physical Review Letters, 2019Co-Authors: K J Kelly, J A Gomez, M Devlin, D Neudecker, Patrick Talou, M C White, J. M. O'donnell, A E Lovell, T. Kawano, R C HaightAbstract:: The physical properties of Neutrons emitted from Neutron-induced Fission are fundamental to our understanding of nuclear Fission. However, while state-of-the-art Fission models still incorporate isotropic Fission Neutron spectra, it is believed that the preequilibrium preFission component of these spectra is strongly anisotropic. The lack of experimental guidance on this feature has not motivated incorporation of anisotropic Neutron spectra in Fission models, though any significant anisotropy would impact descriptions of a Fissioning system. In the present work, an excess of counts at high energies in the Fission Neutron spectrum of ^{239}Pu is clearly observed and identified as an excess of the preequilibrium preFission distribution above the postFission Neutron spectrum. This excess is separated from the underlying postFission Neutron spectrum, and its angular distribution is determined as a function in incident Neutron energy and outgoing Neutron detection angle. Comparison with Neutron scattering models provides the first experimental evidence that the preequilibrium angular distribution is uncorrelated with the Fission axis. The results presented here also impact the interpretation of several influential prompt Fission Neutron spectrum measurements.
-
The 235 U prompt Fission Neutron spectrum measured by the Chi-Nu project at LANSCE
EPJ Web of Conferences, 2017Co-Authors: J A Gomez, K J Kelly, M Devlin, R C Haight, J. M. O'donnell, T.n. Taddeucci, Shea Mosby, Hye Young Lee, N. Fotiades, D NeudeckerAbstract:The Chi-Nu experiment aims to accurately measure the prompt Fission Neutron spectrum for the major actinides. At the Los Alamos Neutron Science Center (LANSCE), Fission can be induced with Neutrons ranging from 0.7 MeV and above. Using a two arm time-of-flight (TOF) technique, the Fission Neutrons are measured in one of two arrays: a 22-6 Li glass array for lower energies, or a 54-liquid scintillator array for outgoing energies of 0.5 MeV and greater. Presented here are the collaboration's preliminary efforts at measuring the 235 U PFNS.
-
prompt Fission Neutron spectra of actinides
Nuclear Data Sheets, 2016Co-Authors: R Capote, D Neudecker, Franzjosef Hambsch, Stephan Oberstedt, Yong-jing Chen, N. Kornilov, B Morillon, J P Lestone, O Litaize, Takaaki OhsawaAbstract:The energy spectrum of prompt Neutrons emitted in Fission (PFNS) plays a very important role in nuclear science and technology. A Coordinated Research Project (CRP) “Evaluation of Prompt Fission Neutron Spectra of Actinides”was established by the IAEA Nuclear Data Section in 2009, with the major goal to produce new PFNS evaluations with uncertainties for actinide nuclei. The following technical areas were addressed: (i) experiments and uncertainty quantification (UQ): New data for Neutron-induced Fission of 233U, 235U, 238U, and 239Pu have been measured, and older data have been compiled and reassessed. There is evidence from the experimental work of this CRP that a very small percentage of Neutrons emitted in Fission are actually scission Neutrons; (ii) modeling: The Los Alamos model (LAM) continues to be the workhorse for PFNS evaluations. Monte Carlo models have been developed that describe the Fission phenomena microscopically, but further development is needed to produce PFNS evaluations meeting the uncertainty targets; (iii) evaluation methodologies: PFNS evaluations rely on the use of the least-squares techniques for merging experimental and model data. Considerable insight was achieved on how to deal with the problem of too small uncertainties in PFNS evaluations. The importance of considering that all experimental PFNS datamore » are “shape” data was stressed; (iv) PFNS evaluations: New evaluations, including covariance data, were generated for major actinides including 1) non-model GMA evaluations of the 235U(nth,f), 239Pu(nth,f), and 233U(nth,f) PFNS based exclusively on experimental data (0.02 ≤ E ≤ 10 MeV), which resulted in PFNS average energies E of 2.00±0.01, 2.073±0.010, and 2.030±0.013 MeV, respectively; 2) LAM evaluations of Neutron-induced Fission spectra on uranium and plutonium targets with improved UQ for incident energies from thermal up to 30 MeV; and 3) Point-by-Point calculations for 232Th, 234U and 237Np targets; and (v) data testing: Spectrum averaged cross sections (SACS) calculated for the evaluated 235U(nth,f) PFN field agree within uncertainties with evaluated SACS experimental data. Despite the observed reduction of the PFNS E by about 30 keV for Neutron-induced Fission of 233U, 235U, and 239Pu, the criticality benchmark outcomes suggested that new evaluations can achieve the same (or better) integral performance with respect to existing evaluations, but the strong compensating effects observed need to be addressed. Summarizing, this project has significantly improved PFNS evaluations and evaluation methodology, provided new PFNS data for applications, and also highlighted the areas for future research« less
Patrick Talou - One of the best experts on this subject based on the ideXlab platform.
-
preequilibrium asymmetries in the 239 pu n f prompt Fission Neutron spectrum
Physical Review Letters, 2019Co-Authors: K J Kelly, J M Odonnell, J A Gomez, M Devlin, D Neudecker, Patrick Talou, M C White, A E Lovell, T. Kawano, R C HaightAbstract:: The physical properties of Neutrons emitted from Neutron-induced Fission are fundamental to our understanding of nuclear Fission. However, while state-of-the-art Fission models still incorporate isotropic Fission Neutron spectra, it is believed that the preequilibrium preFission component of these spectra is strongly anisotropic. The lack of experimental guidance on this feature has not motivated incorporation of anisotropic Neutron spectra in Fission models, though any significant anisotropy would impact descriptions of a Fissioning system. In the present work, an excess of counts at high energies in the Fission Neutron spectrum of ^{239}Pu is clearly observed and identified as an excess of the preequilibrium preFission distribution above the postFission Neutron spectrum. This excess is separated from the underlying postFission Neutron spectrum, and its angular distribution is determined as a function in incident Neutron energy and outgoing Neutron detection angle. Comparison with Neutron scattering models provides the first experimental evidence that the preequilibrium angular distribution is uncorrelated with the Fission axis. The results presented here also impact the interpretation of several influential prompt Fission Neutron spectrum measurements.
-
Preequilibrium Asymmetries in the ^{239}Pu(n,f) Prompt Fission Neutron Spectrum.
Physical Review Letters, 2019Co-Authors: K J Kelly, J A Gomez, M Devlin, D Neudecker, Patrick Talou, M C White, J. M. O'donnell, A E Lovell, T. Kawano, R C HaightAbstract:: The physical properties of Neutrons emitted from Neutron-induced Fission are fundamental to our understanding of nuclear Fission. However, while state-of-the-art Fission models still incorporate isotropic Fission Neutron spectra, it is believed that the preequilibrium preFission component of these spectra is strongly anisotropic. The lack of experimental guidance on this feature has not motivated incorporation of anisotropic Neutron spectra in Fission models, though any significant anisotropy would impact descriptions of a Fissioning system. In the present work, an excess of counts at high energies in the Fission Neutron spectrum of ^{239}Pu is clearly observed and identified as an excess of the preequilibrium preFission distribution above the postFission Neutron spectrum. This excess is separated from the underlying postFission Neutron spectrum, and its angular distribution is determined as a function in incident Neutron energy and outgoing Neutron detection angle. Comparison with Neutron scattering models provides the first experimental evidence that the preequilibrium angular distribution is uncorrelated with the Fission axis. The results presented here also impact the interpretation of several influential prompt Fission Neutron spectrum measurements.
-
evaluation and uncertainty quantification of prompt Fission Neutron spectra of uranium and plutonium isotopes
Nuclear Science and Engineering, 2013Co-Authors: Patrick Talou, T. Kawano, Mike Rising, Anil K. PrinjaAbstract:AbstractThe prompt Fission Neutron spectra (PFNS) of the low-incident-energy Neutron-induced Fission reactions n + 229-238U and n + 235-242Pu have been systematically evaluated using differential experimental data and the Los Alamos model (LA model). Using the first-order, linear Kalman filter, the LA model parameters are constrained using the experimental data and an evaluation of the PFNS and its uncertainties across a suite of isotopes’ results. Correlations between isotopes of each actinide are presented through the model parameter correlations, and the resulting evaluations can be used to fill in inconsistencies within the ENDF/B-VII.1 library where PFNS data are scarce or in need of an update.
-
Systematic Quantification of Uncertainties for Evaluated Prompt Fission Neutron Spectra and Multiplicities
EPJ Web of Conferences, 2012Co-Authors: Patrick Talou, Mike Rising, Toshihiko Kawano, Anil K. PrinjaAbstract:Uncertainties associated with evaluated average prompt Fission Neutron spectra and multiplicities are obtained for a suite of actinides in the Los Alamos model formalism. Systematics for the model input parameters are taken from the literature and used as prior values in a Bayesian updating procedure. Posterior systematics as well as associated posterior uncertainties are inferred. In addition, cross-isotope correlations are evaluated for the first time. The quantification of uncertainties associated with advanced Monte Carlo Hauser-Feshbach calculations of prompt Fission Neutron spectra is also discussed.
-
uncertainty quantification of prompt Fission Neutron spectrum for n 0 5 mev 239pu
Nuclear Science and Engineering, 2010Co-Authors: Patrick Talou, M C White, T. Kawano, D.g. Madland, A C Kahler, Donald Kent Parsons, R C Little, M B ChadwickAbstract:AbstractUncertainties associated with the prompt Fission Neutron spectrum (PFNS) of n(0.5 MeV) + 239Pu evaluated for the ENDF/B-VII.0 library are estimated using known experimental information and model parameter uncertainties in the framework of the Madland-Nix model. The model parameters used for the ENDF/B-VII.0 evaluation are also used in the present work. A covariance matrix is obtained, and its eigenvalues are estimated. Sampled spectra are then used in PARTISN transport simulations to infer the impact of PFNS uncertainties on the calculation of the multiplication factor keff in the Jezebel critical assembly. The present evaluated PFNS uncertainties lead to ˜0.24% uncertainty in the Jezebel keff. Finally, multigroup covariance matrices are produced in 33- and 590-group structures.
M C White - One of the best experts on this subject based on the ideXlab platform.
-
preequilibrium asymmetries in the 239 pu n f prompt Fission Neutron spectrum
Physical Review Letters, 2019Co-Authors: K J Kelly, J M Odonnell, J A Gomez, M Devlin, D Neudecker, Patrick Talou, M C White, A E Lovell, T. Kawano, R C HaightAbstract:: The physical properties of Neutrons emitted from Neutron-induced Fission are fundamental to our understanding of nuclear Fission. However, while state-of-the-art Fission models still incorporate isotropic Fission Neutron spectra, it is believed that the preequilibrium preFission component of these spectra is strongly anisotropic. The lack of experimental guidance on this feature has not motivated incorporation of anisotropic Neutron spectra in Fission models, though any significant anisotropy would impact descriptions of a Fissioning system. In the present work, an excess of counts at high energies in the Fission Neutron spectrum of ^{239}Pu is clearly observed and identified as an excess of the preequilibrium preFission distribution above the postFission Neutron spectrum. This excess is separated from the underlying postFission Neutron spectrum, and its angular distribution is determined as a function in incident Neutron energy and outgoing Neutron detection angle. Comparison with Neutron scattering models provides the first experimental evidence that the preequilibrium angular distribution is uncorrelated with the Fission axis. The results presented here also impact the interpretation of several influential prompt Fission Neutron spectrum measurements.
-
Preequilibrium Asymmetries in the ^{239}Pu(n,f) Prompt Fission Neutron Spectrum.
Physical Review Letters, 2019Co-Authors: K J Kelly, J A Gomez, M Devlin, D Neudecker, Patrick Talou, M C White, J. M. O'donnell, A E Lovell, T. Kawano, R C HaightAbstract:: The physical properties of Neutrons emitted from Neutron-induced Fission are fundamental to our understanding of nuclear Fission. However, while state-of-the-art Fission models still incorporate isotropic Fission Neutron spectra, it is believed that the preequilibrium preFission component of these spectra is strongly anisotropic. The lack of experimental guidance on this feature has not motivated incorporation of anisotropic Neutron spectra in Fission models, though any significant anisotropy would impact descriptions of a Fissioning system. In the present work, an excess of counts at high energies in the Fission Neutron spectrum of ^{239}Pu is clearly observed and identified as an excess of the preequilibrium preFission distribution above the postFission Neutron spectrum. This excess is separated from the underlying postFission Neutron spectrum, and its angular distribution is determined as a function in incident Neutron energy and outgoing Neutron detection angle. Comparison with Neutron scattering models provides the first experimental evidence that the preequilibrium angular distribution is uncorrelated with the Fission axis. The results presented here also impact the interpretation of several influential prompt Fission Neutron spectrum measurements.
-
the need for precise and well documented experimental data on prompt Fission Neutron spectra from Neutron induced Fission of 239pu
Nuclear Data Sheets, 2016Co-Authors: D Neudecker, M C White, R C Haight, T.n. Taddeucci, Hye Young Lee, M E RisingAbstract:The spectrum of Neutrons emitted promptly after 239Pu(n,f)—a so-called prompt Fission Neutron spectrum (PFNS)—is a quantity of high interest, for instance, for reactor physics and global security. However, there are only few experimental data sets available that are suitable for evaluations. In addition, some of those data sets differ by more than their 1-σ uncertainty boundaries. We present the results of MCNP studies indicating that these differences are partly caused by underestimated multiple scattering contributions, over-corrected background, and inconsistent deconvolution methods. A detailed uncertainty quantification for suitable experimental data was undertaken including these effects, and test-evaluations were performed with the improved uncertainty information. The test-evaluations illustrate that the inadequately estimated effects and detailed uncertainty quantification have an impact on the evaluated PFNS and associated uncertainties as well as the Neutron multiplicity of selected critical assemblies. A summary of data and documentation needs to improve the quality of the experimental database is provided based on the results of simulations and test-evaluations. Furthermore, given the possibly substantial distortion of the PFNS by multiple scattering and background effects, special care should be taken to reduce these effects in future measurements, e.g., by measuring the 239Pu PFNS as a ratio to either the 235Umore » or 252Cf PFNS.« less
-
multiple scattering corrections to measurements of the prompt Fission Neutron spectrum
Nuclear Data Sheets, 2015Co-Authors: T.n. Taddeucci, J M Odonnell, M Devlin, D Neudecker, M C White, R C Haight, B A Perdue, Nikolaos Fotiadis, J L Ullmann, R O NelsonAbstract:Abstract The Chi-Nu project, conducted jointly by LANL and LLNL, aims to measure the shape of the prompt Fission Neutron spectrum (PFNS) for Fission of 239Pu induced by Neutrons from 50 keV to 15 MeV with accuracies of 3–5% in the outgoing energy from 50 keV to 9 MeV and 15% from 9 to 15 MeV. In order to meet this goal, detailed Monte Carlo simulations are being used to assess the importance and effect of every component in the experimental configuration. As part of this effort, we have also simulated some past PFNS measurements to identify possible sources of systematic error. We find that multiple scattering plays an important role in the target geometry, collimators, and detector response and that past experiments probably underestimated the extent of this effect.
-
uncertainty quantification of prompt Fission Neutron spectrum for n 0 5 mev 239pu
Nuclear Science and Engineering, 2010Co-Authors: Patrick Talou, M C White, T. Kawano, D.g. Madland, A C Kahler, Donald Kent Parsons, R C Little, M B ChadwickAbstract:AbstractUncertainties associated with the prompt Fission Neutron spectrum (PFNS) of n(0.5 MeV) + 239Pu evaluated for the ENDF/B-VII.0 library are estimated using known experimental information and model parameter uncertainties in the framework of the Madland-Nix model. The model parameters used for the ENDF/B-VII.0 evaluation are also used in the present work. A covariance matrix is obtained, and its eigenvalues are estimated. Sampled spectra are then used in PARTISN transport simulations to infer the impact of PFNS uncertainties on the calculation of the multiplication factor keff in the Jezebel critical assembly. The present evaluated PFNS uncertainties lead to ˜0.24% uncertainty in the Jezebel keff. Finally, multigroup covariance matrices are produced in 33- and 590-group structures.