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arXiv 2021年

作者： Schnabel, Georg Capote, Roberto Koning, Arjan Brown, David NAPC–Nuclear Data Section International Atomic Energy Agency Vienna Austria National Nuclear Data Center Brookhaven National Laboratory UptonNY11973-5000 United States

Bayesian networks are graphical models to represent the deterministic and probabilistic relationships between variables within the Bayesian framework. The knowledge of all variables can be updated using new information about some of the variables. The Bayesian Generalized Linear Least Squares method can be regarded as an inference method for Bayesian networks of variables with multivariate normal priors and linear relationships between them. We show that relying explicitly on the Bayesian network interpretation enables large scale inference and gives more flexibility in incorporating prior assumptions and constraints into the nuclear data evaluation process, such as the constraints that some cross sections equal linear combinations of other cross sections and that all cross sections must be non-negative. The latter constraint is accounted for by a nonlinear transformation and therefore we also discuss inference in Bayesian networks with non-linear relationships between variables. Using Bayesian networks, the evaluation process yields more detailed information, such as posterior estimates and uncertainties of all statistical and systematic errors associated with the experiments. We further elaborate on a sparse Gaussian process construction that can be well integrated into the Bayesian network framework and applied to, e.g., the modeling of energy-dependent model parameters, model deficiencies of the physics model or energy-dependent systematic errors of experiments. We present three proof-of-concept examples that emerged in the context of the neutron data standards project and in the ongoing international evaluation efforts of 56Fe. In the first example we demonstrate the modelization and explicit estimation of relative energy-dependent error components associated with experimental datasets. Then we show that Bayesian networks in combination with the outlined Gaussian process construction may be applied to an evaluation of 56Fe in the energy range between one and tw

关键词： Bayesian networks

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Extension of the Hauser-Feshbach fission fragment decay model to multichance fission

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Physical Review C 2021年第1期103卷 014615-014615页

作者： A. E. Lovell T. Kawano S. Okumura I. Stetcu M. R. Mumpower P. Talou Los Alamos National Laboratory Los Alamos New Mexico 87545 USA NAPC–Nuclear Data Section International Atomic Energy Agency Vienna A-1400 Austria

The Hauser-Feshbach fission fragment decay model, HF3D, which calculates the statistical decay of fission fragments, has been expanded to include multichance fission, up to neutron incident energies of 20 MeV. The deterministic decay takes as input prescission quantities—fission probabilities and the average energy causing fission—and postscission quantities—yields in mass, charge, total kinetic energy, spin, and parity. From these fission fragment initial conditions, the full decay is followed through both prompt and delayed particle emissions, allowing for the calculation of prompt neutron and γ properties, such as multiplicity and energy distributions, both independent and cumulative fission yields, and delayed neutron observables. In this work, we describe the implementation of multichance fission in the HF3D model, and show an example of prompt and delayed quantities beyond first-chance fission, using the example of neutron-induced fission on U235. This expansion represents significant progress in consistently modeling the emission of prompt and delayed particles from fissile systems.

关键词： Fission Models & methods for nuclear reactions Nucleon induced nuclear reactions A ≥ 220

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Influence of nonstatistical properties in nuclear structure on emission of prompt fission neutrons

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Physical Review C 2021年第1期104卷 014611-014611页

作者： T. Kawano S. Okumura A. E. Lovell I. Stetcu P. Talou Los Alamos National Laboratory Los Alamos New Mexico 87545 USA NAPC–Nuclear Data Section International Atomic Energy Agency Vienna A-1400 Austria

The Hauser-Feshbach fission-fragment decay (HFD3) model is extended to calculate the prompt fission neutron spectrum (PFNS) for the thermal-neutron-induced fission on U235, where the evaporated neutrons from all possible fission-fragment pairs are aggregated. By studying model parameter sensitivities on the calculated PFNS as well as nonstatistical behavior of low-lying discrete level spin distribution, we conclude that discrepancies between the aggregation calculation and the experimental PFNS seen at higher neutron emission energies can be attributed to both the primary fission-fragment yield distribution and the possible high spin states that are not predicted by the statistical theory of nuclear structure.

关键词： Fission nuclear reactions Nucleon induced nuclear reactions

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An iron evaluation story: from TALYS model parameters to validation on the ASPIS benchmark with the Monte Carlo code TRIPOLI-4®

An iron evaluation story: from TALYS model parameters to val...

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2022 International Conference on Physics of Reactors, PHYSOR 2022

作者： Raffuzzi, Valeria Sublet, Jean-Christophe Jouanne, Cédric Koning, Arjan Rochman, Dimitri University of Cambridge Trumpington Street CambridgeCB2 1PZ United Kingdom IAEA NAPC-Nuclear Data Section Wagramer Str. 5 Vienna1220 Austria Université Paris-Saclay CEA Service d'Etudes des Réacteurs et de Mathématiques Appliquées Gif-sur-Yvette91191 France PSI Forschungsstrasse 111 Villigen5232 Switzerland

ISBN: (纸本)9780894487873

Iron is a widespread structural material in nuclear applications. However, some benchmark studies show that for many libraries, including TENDL-2019, producing good iron evaluations is still an open challenge. This work aims at improving TENDL-2019 56Fe and 54Fe evaluations through feedbacks from experimental data and Monte Carlo results of the iron benchmark ASPIS. Part of the T6 code infrastructure was used to produce the evaluations. In the new evaluations, particular attention to resonance parameters and formalism was paid to address the importance of elastic scattering. The total inelastic scattering and inelastic continuum cross sections were shaped by modifying the input parameters of TALYS, one of the T6 codes. Additionally, it was necessary to normalise some reaction channels to those of JENDL-4.0. With the new files ASPIS results, obtained with the Monte Carlo code TRIPOLI-4®, improved noticeably compared to TENDL-2019. The evaluations and parameter setting modifications are to be included into TENDL-2021. © 2022 Proceedings of the International Conference on Physics of Reactors, PHYSOR 2022. All Rights Reserved.

关键词： ASPIS benchmark Iron Evaluation nuclear data TALYS TENDL

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Modeling Compound nuclear Reactions with EMPIRE 6th

Modeling Compound Nuclear Reactions with EMPIRE

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6th International Workshop on Compound-nuclear Reactions and Related Topics, CNR 2018

作者： Herman, M. Capote, R. Carlson, B.V. Sin, M. Trkov, A. Theoretical Division Los Alamos National Laboratory Los AlamosNM United States NAPC-Nuclear Data Section International Atomic Energy Agency Vienna Austria Instituto Tecnológico da Aeronáutica São José dos Campos SP Brazil Faculty of Physics University of Bucharest Bucharest Romania

ISBN: (纸本)9783030580810

EMPIRE by Herman et al. (Nucl data Sheets 108:2655, 2007) is a modular system of nuclear reaction codes, comprising various nuclear models, and designed for calculations over a broad range of energies and incident particles. A projectile can be a neutron, a proton, an ion, or a photon. The energy range extends from the beginning of the unresolved resonance region for neutron-induced reactions and goes up to several hundred MeV for heavy-ion induced reactions. The code accounts for the major nuclear reaction mechanisms, including direct, pre-equilibrium, and compound nucleus ones. Direct reactions are described by a generalized optical model or by a coupled channels approach. The pre-equilibrium mechanism can be treated by several quantum mechanical and semiclassical models. The compound nucleus decay is described by a full featured Hauser-Feshbach model with γ-cascade and width fluctuations. Advanced treatment of the fission channel takes into account transmission through a multiple-humped fission barrier with absorption in the wells. Here we will discuss the general capabilities of the code to model nuclear reactions and provide several examples of its use in modeling pre-compound and compound nuclear decay. © 2021, This is a U.S. government work and not under copyright protection in the U.S.;foreign copyright protection may apply.

关键词： nuclear reactions

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Influence of non-statistical properties in nuclear structure on emission of prompt fission neutrons

arXiv

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arXiv 2021年

作者： Kawano, Toshihiko Okumura, Shin Lovell, Amy E. Stetcu, Ionel Talou, Patrick Los Alamos National Laboratory Los AlamosNM87545 United States NAPC-Nuclear Data Section International Atomic Energy Agency ViennaA-1400 Austria

The Hauser-Feshbach Fission Fragment Decay (HF3D) model is extended to calculate the prompt fission neutron spectrum (PFNS) for the thermal neutron induced fission on 235U, where the evaporated neutrons from all possible fission fragment pairs are aggregated. By studying model parameter sensitivities on the calculated PFNS, as well as non-statistical behavior of low-lying discrete level spin distribution, we conclude that discrepancies between the aggregation calculation and the experimental PFNS seen at higher neutron emission energies can be attributed to both the primary fission fragment yield distribution and the possible high spin states that are not predicted by the statistical theory of nuclear structure. Copyright © 2021, The Authors. All rights reserved.

关键词： Fission reactions

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Cassini-oval description of the multidimensional potential energy surface for U236: Role of octupole deformation and calculation of the most probable fission path

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Physical Review C 2023年第3期107卷 034608-034608页

作者： K. Okada T. Wada R. Capote N. Carjan Department of Pure and Applied Physics Kansai University 564-8680 Suita Osaka Japan NAPC–Nuclear Data Section International Atomic Energy Agency 1400 Vienna Austria Joint Institute for Nuclear Research 141980 Dubna Moscow Region Russia Centre d'Etudes Nucleaires de Bordeaux-Gradignan UMR 5797 CNRS/IN2P3-University Bordeaux I BP 120 33175 Gradignan Cedex France Horia Hulubei - National Institute for Nuclear Physics and Engineering P.O.Box MG-6 RO-76900 Bucharest Romania

Multidimensional potential energy surfaces (PES) are calculated using the microscopic-macroscopic approach. The nuclear shapes are described by Cassinian ovals generalized by the inclusion of α1, α3, and α4 shape parameters in addition to the main fission coordinate α. The influence of the octupole deformation (α3) on the PES is studied in the case of the nuclear fission of U236. It is found that α3 plays an important role in the last stage of the fission process; for instance, it lowers the third minimum and the third barrier. Two methods to calculate the static fission path are investigated. They are found to be consistent in the sense that they lead to the same fission barrier. In certain subspaces, the least energy paths from the ground state to scission present discontinuities around one of the saddles. They are caused by sharp changes in the nuclear shapes involved occurring without a change in energy. Such transitions are smoothed out by the principle of stationary action, which transforms a discontinuous path into a continuous one. Finally, various macroscopic models have been employed in order to study their influence on the energies and positions of the saddles and the minima.

关键词： Fission Models & methods for nuclear reactions nuclear reactions

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Energy dependent calculations of fission product, prompt, and delayed neutron yields for neutron induced fission on 235U, 238U, and 239Pu

arXiv

引用

arXiv 2021年

作者： Okumura, S. Kawano, T. Lovell, A.E. Yoshida, T. NAPC-Nuclear Data Section International Atomic Energy Agency ViennaA-1400 Austria Theoretical Division Los Alamos National Laboratory Los AlamosNM87545 United States Laboratory for Advanced Nuclear Energy Tokyo Institute of Technology Tokyo152-8550 Japan

We perform energy dependent calculations of independent and cumulative fission product yields for 235U, 238U, and 239Pu in the first chance fission region. Starting with the primary fission fragment distributions taken from available experimental data and analytical functions based on assumptions for the excitation energy and spin-parity distributions, the Hauser-Feshbach statistical decay treatment for fission fragment de-excitation is applied to more than 1,000 fission fragments for the incident neutron energies up to 5 MeV. The calculated independent fission product yields are then used as an input of β-decay to produce the cumulative yield, and summation calculations are performed. Model parameters in these procedures are adjusted by applying the Bayesian technique at the thermal energy for 235U and 239Pu and in the fast energy range for 238U. The calculated fission observable quantities, such as the energy-dependent fission yields, and prompt and delayed neutron yields, are compared with available experimental data. We also study a possible impact of the second chance fission opening on the energy dependence of the delayed neutron yield by extrapolating the calculation. Copyright © 2021, The Authors. All rights reserved.

关键词： Neutrons

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Connection of four-dimensional Langevin model and Hauser-Feshbach theory to describe statistical decay of fission fragments

arXiv

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arXiv 2023年

作者： Fujio, Kazuki Okumura, Shin Ishizuka, Chikako Chiba, Satoshi Katabuchi, Tatsuya Nuclear Engineering Course Department of Transdisciplinary Science and Technology School of Environment and Society Tokyo Institute of Technology 2-12-1 Ookayama Meguro Tokyo152-8550 Japan NAPC-Nuclear Data Section International Atomic Energy Agency Vienna International Centre Vienna1400 Austria Institute of Innovative Research Tokyo Institute of Technology 2-12-1 Ookayama Meguro Tokyo152-8550 Japan NAT Research Center NAT 3129-45 Hirahara Muramatsu Tokai Ibaraki Naka319-1112 Japan

We developed a method superposing two different fission modes calculated in a four-dimensional Langevin model to obtain more accurate fission fragment yield and total kinetic energy (TKE). The two fission modes correspond to the standard I and standard II modes reported by Brosa et al., and parameters in the Langevin model and the superposing ratio were determined to reproduce the fission fragment yield of 240Pu of spontaneous fission. We also investigated the fission fragment yields and the TKEs of other Pu isotopes by using the same Langevin parameters and different superposing ratios, such as spontaneous fission of 238,242Pu and neutron-induced fission of 239Pu. The prompt fission observables, such as the neutron multiplicity, the prompt fission neutron spectrum, and the independent fission product yield were calculated in the Hauser-Feshbach statistical decay model implemented in a nuclear reaction code TALYS with 239Pu(n,f) in the incident energies ranging from thermal energy up to 5 MeV. The calculated fission observables qualitatively reproduce several known trends while calculated results have quantitative discrepancies between reported data. Although more improvements are needed for the most important nuclides, it turned out that our approach has the capability to provide prompt fission observables for difficult-to-measure nuclides. Copyright © 2023, The Authors. All rights reserved.

关键词： Isotopes

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Modeling photon-induced reactions on U233–238 actinide targets

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Physical Review C 2021年第5期103卷 054605-054605页

作者： M. Sin R. Capote M. W. Herman A. Trkov B. V. Carlson University of Bucharest Faculty of Physics Bucharest-Magurele RO-077125 Romania NAPC–Nuclear Data Section International Atomic Energy Agency A-1400 Vienna Austria Los Alamos National Laboratory Los Alamos New Mexico 87544 USA Instituto Tecnológico de Aeronáutica Brazil

Comprehensive calculations of photon-induced reactions on U233–238 targets for incident photon energies from 3 up to 30 MeV are undertaken with the statistical model code empire-3.2 Malta. Results are compared with the experimental data from EXFOR and with the current evaluations. The differences and the similarities between the models and parameters used in calculations of photon- and neutron-induced reactions on the same nuclei are discussed with focus on fission. The role of the extended optical model for fission that includes partial damping in the continuum in improving the description of the measured data is pointed out.

关键词： Fission Models & methods for nuclear reactions Photonuclear reactions A ≥ 220 nuclear reaction analysis

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