The Experts below are selected from a list of 31809 Experts worldwide ranked by ideXlab platform
B Pritychenko - One of the best experts on this subject based on the ideXlab platform.
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calculations of nuclear astrophysics and californium fission Neutron spectrum averaged Cross Section uncertainties using endf b vii 1 jeff 3 1 2 jendl 4 0 and low fidelity covariances
Nuclear Data Sheets, 2015Co-Authors: B PritychenkoAbstract:Abstract Nuclear astrophysics and californium fission Neutron spectrum averaged Cross Sections and their uncertainties for ENDF materials have been calculated. Absolute values were deduced with Maxwellian and Mannhart spectra, while uncertainties are based on ENDF/B-VII.1, JEFF-3.1.2, JENDL-4.0 and Low-Fidelity covariances. These quantities are compared with available data, independent benchmarks, EXFOR library, and analyzed for a wide range of cases. Recommendations for Neutron Cross Section covariances are given and implications are discussed.
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calculations of nuclear astrophysics and californium Neutron Cross Section uncertainties using endf b vii 1 jeff 3 1 2 jendl 4 0 and low fidelity covariances
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: B PritychenkoAbstract:Nuclear astrophysics and californium Neutron spectrum Cross Sections and their uncertainties for ENDF materials have been calculated. Absolute values were deduced with Maxwellian and Mannhart spectra, while uncertainties are based on ENDF/B-VII.1, JEFF-3.1.2, JENDL-4.0 and Low-Fidelity covariances. These quantities are compared with available data, independent benchmarks, EXFOR library, and analyzed for a wide range of cases. Recommendations for Neutron Cross Section covariances are given and implications are discussed.
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sigma web retrieval interface for nuclear reaction data
Nuclear Data Sheets, 2008Co-Authors: B Pritychenko, A A SonzogniAbstract:The authors present Sigma, a Web-rich application which provides user-friendly access in processing and plotting of the evaluated and experimental nuclear reaction data stored in the ENDF-6 and EXFOR formats. The main interface includes browsing using a periodic table and a directory tree, basic and advanced search capabilities, interactive plots of Cross Sections, angular distributions and spectra, comparisons between evaluated and experimental data, computations between different Cross Section sets. Interactive energy-angle, Neutron Cross Section uncertainties plots and visualization of covariance matrices are under development. Sigma is publicly available at the National Nuclear Data Center website at www.nndc.bnl.gov/sigma.
D L Smith - One of the best experts on this subject based on the ideXlab platform.
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a new formulation of the unified monte carlo approach umc b and Cross Section evaluation for the dosimetry reaction 55 mn n γ 56 mn
Journal of Astm International, 2012Co-Authors: R Capote, D L Smith, A Trkov, Mehdi MeghzifeneAbstract:Two relatively new approaches to Neutron Cross Section data evaluation are described. They are known collectively as Unified Monte Carlo (versions UMC-G and UMC-B). Comparisons are made between these two methods, as well as with the well-known generalized least-squares (GLSQ) technique, through the use of simple, hypothetical (toy) examples. These new Monte Carlo methods are based on stochastic sampling of probability functions that are constructed with the use of theoretical and experimental data by applying the principle of maximum entropy. No further assumptions are involved in either UMC-G or UMC-B. However, the GLSQ procedure requires the linearization of non-linear terms, such as those that occur when Cross Section ratio data are included in an evaluation. It is shown that these two stochastic techniques yield results that agree well with each other, and with the GLSQ method, when linear data are involved, or when the perturbations due to data discrepancies and nonlinearity effects are small. Otherwise, there can be noticeable differences. The present investigation also demonstrates, as observed in earlier work, that the least-squares approach breaks down when these conditions are not satisfied. This paper also presents an actual evaluation of the 55Mn(n,γ)56Mn Neutron dosimetry reaction Cross Section in the energy range from 100 keV to 20 MeV, which was performed using both GLSQ and UMC-G approaches.
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international evaluation of Neutron Cross Section standards
Nuclear Data Sheets, 2009Co-Authors: Allan D Carlson, D L Smith, V G Pronyaev, N M Larson, Zhenpeng Chen, G M Hale, Franzjosef Hambsch, E V Gai, S A Badikov, T KawanoAbstract:Neutron Cross Section standards are the basis for the determination of most Neutron Cross Sections. They are used for both measurements and evaluations of Neutron Cross Sections. Not many Cross Sections can be obtained absolutely – most Cross Sections are measured relative to the Cross Section standards and converted using evaluations of the standards. The previous complete evaluation of the Neutron Cross Section standards was finished in 1987 and disseminated as the NEANDC/INDC and ENDF/B-VI standards. R-matrix model fits for the light elements and non-model least-squares fits for all the Cross Sections in the evaluation were the basis of the combined fits for all of the data. Some important reactions and constants are not standards, but they assist greatly in the determination of the standard Cross Sections and reduce their uncertainties – these data were also included in the combined fits. The largest experimental database used in the evaluation was prepared by Poenitz and included about 400 sets of experimental data with covariance matrices of uncertainties that account for all Cross-energy, Cross-reaction and Cross-material correlations. For the evaluation GMA, a least-squares code developed by Poenitz, was used to fit all types of Cross Sections (absolute and shape), their ratios, spectrum-averaged Cross Sections and thermal constants in one full analysis. But, the uncertainties derived in this manner, and especially those obtained in the R-matrix model fits, have been judged to be too low and unrealistic. These uncertainties were substantially increased prior to their release in the recommended data files of 1987. Modified percentage uncertainties were reassigned by the United States Cross Section Evaluation Working Group's Standards Subcommittee for a wide range of energies, and no covariance (or correlation) matrices were supplied at that time. The need to re-evaluate the Cross Section standards is based on the appearance of a significant amount of precise experimental data and improved developments in the methodology of analysis and evaluation. Initial efforts to produce a new evaluation were made by the United States Cross Section Evaluation Working Group which formed a Task Force. It was realized that international cooperation would be needed to produce the evaluation. The Working Party on International Evaluation Cooperation of the Nuclear Energy Agency Nuclear Science Committee formed a Subgroup, and the International Atomic Energy Agency formed a Coordinated Research Project (CRP). These groups worked cooperatively to improve the evaluation process. The major effort in producing the evaluation was through the CRP. The evaluations of the Neutron Cross Section standards were finalized in October 2005. Previous difficulties experienced with a data evaluation problem known as “Peelle's Pertinent Puzzle” create biases in the fit of correlated data, and they have been addressed to reduce this phenomenon. The new evaluations of the Cross Section standards also include covariance matrices of the uncertainties that contain fully justifiable values. The product of this international effort has been adopted as the Neutron standards for ENDF/B-VII.0.
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an investigation of the performance of the unified monte carlo method of Neutron Cross Section data evaluation
Nuclear Data Sheets, 2008Co-Authors: R Capote, D L SmithAbstract:The Unified Monte Carlo method (UMC) has been suggested to avoid certain limitations and approximations inherent to the well-known Generalized Least Squares (GLS) method of nuclear data evaluation. This contribution reports on an investigation of the performance of the UMC method in comparison with the GLS method. This is accomplished by applying both methods to simple examples with few input values that were selected to explore various features of the evaluation process that impact upon the quality of an evaluation. Among the issues explored are: i) convergence of UMC results with the number of Monte Carlo histories and the ranges of sampled values; ii) a comparison of Monte Carlo sampling using the Metropolis scheme and a brute force approach; iii) the effects of large data discrepancies; iv) the effects of large data uncertainties; v) the effects of strong or weak model or experimental data correlations; and vi) the impact of ratio data and integral data. Comparisons are also made of the evaluated results for these examples when the input values are first transformed to comparable logarithmic values prior to performing the evaluation. Some general conclusions that are applicable to more realistic evaluation exercises are offered.
S Carretta - One of the best experts on this subject based on the ideXlab platform.
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Quantum hardware simulating four-dimensional inelastic Neutron scattering
Nature Physics, 2019Co-Authors: A. Chiesa, F. Tacchino, M. Grossi, P. Santini, I. Tavernelli, D. Gerace, S CarrettaAbstract:Inelastic Neutron scattering is used to probe the spin dynamics of molecular nanomagnets, but extensive supporting computations make the technique challenging. Proof-of-principle experiments now show that quantum computers may solve these computations efficiently. Magnetic molecules, modelled as finite-size spin systems, are test-beds for quantum phenomena^ 1 and could constitute key elements in future spintronics devices^ 2 – 5 , long-lasting nanoscale memories^ 6 or noise-resilient quantum computing platforms^ 7 – 10 . Inelastic Neutron scattering is the technique of choice to probe them, characterizing molecular eigenstates on atomic scales^ 11 – 14 . However, although large magnetic molecules can be controllably synthesized^ 15 – 18 , simulating their dynamics and interpreting spectroscopic measurements is challenging because of the exponential scaling of the required resources on a classical computer. Here, we show that quantum computers^ 19 – 22 have the potential to efficiently extract dynamical correlations and the associated magnetic Neutron Cross-Section by simulating prototypical spin systems on a quantum hardware^ 22 . We identify the main gate errors and show the potential scalability of our approach. The synergy between developments in Neutron scattering and quantum processors will help design spin clusters for future applications.
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quantum hardware simulating four dimensional inelastic Neutron scattering
arXiv: Quantum Physics, 2018Co-Authors: A. Chiesa, F. Tacchino, M. Grossi, P. Santini, I. Tavernelli, D. Gerace, S CarrettaAbstract:Magnetic molecules, modelled as finite-size spin systems, are test-beds for quantum phenomena and could constitute key elements in future spintronics devices, long-lasting nanoscale memories or noise-resilient quantum computing platforms. Inelastic Neutron scattering is the technique of choice to probe them, characterizing molecular eigenstates on atomic scales. However, although large magnetic molecules can be controllably synthesized, simulating their dynamics and interpreting spectroscopic measurements is challenging because of the exponential scaling of the required resources on a classical computer. Here, we show that quantum computers have the potential to efficiently extract dynamical correlations and the associated magnetic Neutron Cross-Section by simulating prototypical spin systems on a quantum hardware. We identify the main gate errors and show the potential scalability of our approach. The synergy between developments in Neutron scattering and quantum processors will help design spin clusters for future applications.
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quantum hardware simulating four dimensional inelastic Neutron scattering
arXiv: Quantum Physics, 2018Co-Authors: A. Chiesa, F. Tacchino, M. Grossi, P. Santini, I. Tavernelli, D. Gerace, S CarrettaAbstract:Finite-size spin systems could constitute key elements in future spintronics devices [1-5], long-lasting nano-scale memories [6] or scalable and noise-resilient quantum computing platforms [7-9]. They are also natural test-beds for investigating peculiar quantum phenomena [10]. Inelastic Neutron Scattering is the technique of choice to model these systems. Indeed, it enables an atomic-scale characterization of the molecular eigenstates [11], which can provide unambiguous fingerprints of the spin cluster [12, 13] and can be used to quantify entanglement in supramolecular complexes [14]. However, the full potential of molecular magnetism is still largely unexploited, because large molecules and complex supramolecular structures can be controllably synthesized [15-18], but are poorly understood. In fact, their large Hilbert space precludes the simulation of their dynamics and the interpretation of spectroscopic measurements. Here we show that quantum computers [19-22] can efficiently solve this issue. By simulating prototypical spin systems on the IBM quantum hardware [22], we extract dynamical correlations and the associated magnetic Neutron Cross-Section. From this information we then obtain the degree of entanglement in eigenstates. The synergy between developments in Neutron scattering and processors containing few dozens of qubits will enable a big step forward in the design of spin clusters for fundamental and technological applications.
Hyeongkae Park - One of the best experts on this subject based on the ideXlab platform.
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comparison of multimesh hp fem to interpolation and projection methods for spatial coupling of thermal and Neutron diffusion calculations
Journal of Computational Physics, 2011Co-Authors: Lenka Dubcova, Pavel Solin, Glen Hansen, Hyeongkae ParkAbstract:Multiphysics solution challenges are legion within the field of nuclear reactor design and analysis. One major issue concerns the coupling between heat and Neutron flow (Neutronics) within the reactor assembly. These phenomena are usually very tightly interdependent, as large amounts of heat are quickly produced with an increase in fission events within the fuel, which raises the temperature that affects the Neutron Cross Section of the fuel. Furthermore, there typically is a large diversity of time and spatial scales between mathematical models of heat and Neutronics. Indeed, the different spatial resolution requirements often lead to the use of very different meshes for the two phenomena. As the equations are coupled, one must take care in exchanging solution data between them, or significant error can be introduced into the coupled problem. We propose a novel approach to the discretization of the coupled problem on different meshes based on an adaptive multimesh higher-order finite element method (hp-FEM), and compare it to popular interpolation and projection methods. We show that the multimesh hp-FEM method is significantly more accurate than the interpolation and projection approaches considered in this study.
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comparison of multimesh hp fem to interpolation and projection methods for spatial coupling of reactor thermal and Neutron diffusion calculations
Electrochimica Acta, 2011Co-Authors: Lenka Dubcova, Pavel Solin, Glen Hansen, Hyeongkae ParkAbstract:Multiphysics solution challenges are legion within the ?eld of nuclear reactor design and analysis. One major issue concerns the coupling between heat and Neutron ?ow (Neutronics) within the reactor assembly. These phenomena are usually very tightly interdependent, as large amounts of heat are quickly produced with an increase in ?ssion events within the fuel, which raises the temperature that a?ects the Neutron Cross Section of the fuel. Furthermore, there typically is a large diversity of time and spatial scales between mathematical models of heat and Neutronics. Indeed, the di?erent spatial resolution requirements often lead to the use of very di?erent meshes for the two phenomena. As the equations are coupled, one must take care in exchanging solution data between them, or signi?cant error can be introduced into the coupled problem. We propose a novel approach to the discretization of the coupled problem on di?erent meshes based on an adaptive multimesh higher-order ?nite element method (hp-FEM), and compare it to popular interpolation and projection methods. We show that the multimesh hp-FEM method is signi?cantly more accurate than the interpolation and projection approaches considered in this study.
Olivier Bouland - One of the best experts on this subject based on the ideXlab platform.
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americium 241 phase i reevaluation for jeff 3 1 1 and a step forward
Journal of Nuclear Science and Technology, 2012Co-Authors: David Bernard, Olivier BoulandAbstract:This article reviews the low energy Neutron Cross Section revision and the capture isomeric ratio evaluation of the 241Am Neutron data performed for JEFF-3.1.1. It covers the history of the anterior evaluation made for JEF-2.2 and gives the consistent path used for re-evaluating the resolved resonance parameters from differential measurements and “integral” data feedback. This article highlights the procedure pursued to evaluate the 241Am capture ISOmeric ratio (ISO γ) from 0 to 20 MeV in parallel with a valuable estimation of the associated variances. Monte Carlo-type calculations have been made which predict ISO γ fluctuations over the energy region of the resolved resonances due to the presence of 2 s-wave types exhibiting well separated individual values (estimated to (90 ± 3)% and (76 ± 3)%, respectively, for a 2− and a 3− resonance) and well-resolved γ-multiplicities ( and ). Arguments are developed for using directly pointwise ISO γ data in reactor codes in the form of resonant partial capture cros...