An attempt is made to improve the evaluation of the prompt fission neutron emis- sion from 233U（n, f） reaction for incident neutron energies below 6 MeV. The multi-modal fission approach is applied to the improved v...An attempt is made to improve the evaluation of the prompt fission neutron emis- sion from 233U（n, f） reaction for incident neutron energies below 6 MeV. The multi-modal fission approach is applied to the improved version of Los Alamos model and the point by point model. The prompt fission neutron spectra and the prompt fission neutron as a function of fragment mass （usually named ＂sawtooth＂ data） v（A） are calculated independently for the three most dominant fission modes （standard I, standard II and superlong）, and the total spectra and v（A） are syn- thesized. The multi-modal parameters are determined on the basis of experimental data of fission fragment mass distributions. The present calculation results can describe the experimental data very well, and the proposed treatment is thus a useful tool for prompt fission neutron emission prediction.展开更多
The pre-neutron-emission mass distributions for reaction232Th(n, f) up to 60 MeV are systematically studied with an empirical fission potential model. The energy dependences of the peaks and valleys of the pre-neutron...The pre-neutron-emission mass distributions for reaction232Th(n, f) up to 60 MeV are systematically studied with an empirical fission potential model. The energy dependences of the peaks and valleys of the pre-neutronemission mass distributions are described by the exponential expressions based on the newly measured data. The energy dependence of evaporation neutrons before scission, which plays a crucial role for the reasonable description of the mass distribution, is also considered. Both the double-humped and triple-humped shape of the measured pre-neutronemission mass distributions for reaction232Th(n, f) are reasonably well reproduced at incident energies up to 60 MeV.The mass distributions at unmeasured energies and the critical energies at which the humped pre-neutron-emission mass distributions are transformed into each other are also predicted.展开更多
Knowledge of actinides(n,f) fission process induced by neutron is of importance in the field of nuclear power and nuclear engineering,especially for reactor applications.In this work,fission characteristics of^(238)U(...Knowledge of actinides(n,f) fission process induced by neutron is of importance in the field of nuclear power and nuclear engineering,especially for reactor applications.In this work,fission characteristics of^(238)U(n,f) reaction induced by D-T neutron source were simulated with Geant4 code from multiple perspectives,including the fission production yields,total nubar,kinetic energy distribution,fission neutron spectrum and cumulative γ-ray spectrum of the fission products.The simulation results agree well with the experimental nuclear reaction data(EXFOR) and evaluated nuclear data(ENDF).Mainly,this work was to examine the rationality of the parametric nuclear fission model in Geant4 and to direct our future experimental measurements for the cumulative fission yields of ^(238)U(n,f) reaction.展开更多
当前新型核能利用系统及核数据评价的发展对快中子诱发^(239)Pu裂变核数据提出了更高的精度需求。本工作基于已提出并构建的Potential-driving模型,通过中子诱发^(239)Pu(n,f)裂变驱动势研究,计算了几个典型能量中子诱发^(239)Pu(n,f)...当前新型核能利用系统及核数据评价的发展对快中子诱发^(239)Pu裂变核数据提出了更高的精度需求。本工作基于已提出并构建的Potential-driving模型,通过中子诱发^(239)Pu(n,f)裂变驱动势研究,计算了几个典型能量中子诱发^(239)Pu(n,f)反应发射中子前裂变碎片质量分布,并与实验数据进行了对比。结果显示:Potential-driving模型计算数据能够很好地与实验数据符合。将Potential-driving模型植入GEANT4程序,开展了快中子诱发^(239)Pu(n,f)反应相关的模拟研究,给出了14 Me V中子诱发^(239)Pu(n,f)反应的裂变碎片独立产额质量分布和电荷分布、累积产额质量分布和电荷分布、动能分布、裂变中子能谱以及^(239)Pu(n,f)反应裂变碎片平均总动能随入射中子能量的变化等数据,并与GEANT4程序原有的参数化裂变模型(G4Para Fission Model)模拟结果、ENDF/B-VII.1库评价数据以及实验数据进行了比较。结果显示:所发展的Potential-driving模型能很好地预测快中子诱发^(239)Pu(n,f)反应裂变产物数据,为快中子诱发^(239)Pu(n,f)反应裂变产物核数据的研究提供了一种更可靠的计算方法。展开更多
Properties of prompt fission neutrons from 238U（n, f） are calculated for incident neutron egies below 6 MeV using the multi-modal model, including the prompt fission neutron spectrum, thnere average prompt fission n...Properties of prompt fission neutrons from 238U（n, f） are calculated for incident neutron egies below 6 MeV using the multi-modal model, including the prompt fission neutron spectrum, thnere average prompt fission neutron multiplicity, and the prompt fission neutron multiplicity as a function of the fission fragment mass v（A） （usually named ＂sawtooth＂ data） The three most dominant fission modes are taken into account. The model parameters are determined on the basis of experimental fission fragment data. The predicted results are in good agreement with the experimental data.展开更多
The prompt fission neutron spectra for the neutron-induced fission of 233U for low energy neutrons （below 6 MeV） are calculated using nuclear evaporation theory with a semi-empirical method, in which the partition o...The prompt fission neutron spectra for the neutron-induced fission of 233U for low energy neutrons （below 6 MeV） are calculated using nuclear evaporation theory with a semi-empirical method, in which the partition of the total excitation energy between the fission fragments for the nth＋233U fission reactions is determined by the available experimental and evaluation data. The calculated prompt fission neutron spectra agree well with the experimental data. The proportions of high-energy neutrons of prompt fission neutron spectrum versus incident neutron energies are investigated with the theoretical spectra, and the results are consistent with the systematics. The semi-empirical method could be a useful tool for the prompt evaluation of fission neutron spectra.展开更多
Calculations of prompt fission neutron spectra （PFNS） from the ^235U（n, f） reaction were performed with a semi-empirical method for En = 7.0 and 14.7 MeV neutron energies. The total PFNS were obtained as a superpo...Calculations of prompt fission neutron spectra （PFNS） from the ^235U（n, f） reaction were performed with a semi-empirical method for En = 7.0 and 14.7 MeV neutron energies. The total PFNS were obtained as a superposition of （n,xnf） pre-fission neutron spectra and post-fission spectra of neutrons which were evaporated from fission fragments, and these two kinds of spectra were taken as an expression of the evaporation spectrum. The contributions of （n,xnf） fission neutron spectra on the calculated PFNS were discussed. The results show that emission of one or two neutrons in the （n,nf） or （n,2nf） reactions influences the PFNS shape, and the neutron spectra of the （n,xnf） fission-channel are soft compared with the neutron spectra of the （n,f） fission channel. In addition, analysis of the multiple-chance fission component showed that second-chance fission dominates the PFNS with an incident neutron energy of 14.7 MeV whereas first-chance fission dominates the 7 MeV case.展开更多
Accurate cross sections of neutron induced fission reactions are required in the design of advanced nuclear systems and the development of fission theory.Time projection chambers(TPCs),with their track reconstruction ...Accurate cross sections of neutron induced fission reactions are required in the design of advanced nuclear systems and the development of fission theory.Time projection chambers(TPCs),with their track reconstruction and particle identification capabilities,are considered the best detectors for high-precision fission cross section measurements.The TPC developed by the back-streaming white neutron source(Back-n)team of the China Spallation Neutron Source(CSNS)was used as the fission fragment detector in measurements.In this study,the cross sections of the ^(232)Th(n,f)reaction at five neutron energies in the 4.50−5.40 MeV region were measured.The fission fragments and α particles were well identified using our TPC,which led to a higher detection efficiency of the fission fragments and smaller uncertainty of the measured cross sections.Ours is the first measurement of the ^(232)Th(n,f)reaction using a TPC for the detection of fission fragments.With uncertainties less than 5%,our cross sections are consistent with the data in different evaluation libraries,including JENDL-4.0,ROSFOND-2010,CENDL-3.2,ENDF/B-VⅢ.0,and BROND-3.1,whose uncertainties can be reduced after future improvement of the measurement.展开更多
Abstract： The pre-neutron-emission mass distributions for reaction ^238U（n, f） up to 60 MeV are systematically studied with an empirical fission potential model. The energy dependence of the peaks and valleys of th...Abstract： The pre-neutron-emission mass distributions for reaction ^238U（n, f） up to 60 MeV are systematically studied with an empirical fission potential model. The energy dependence of the peaks and valleys of the pre-neutronemission mass distributions is described by an exponential form based on the newly measured data. The energy dependence of evaporation neutrons before scission is also considered, which plays a crucial role in the reasonable description of the mass distributions. The measured ^238U（n, f） are reasonably well reproduced up to 60 predicted using this approach. data of the pre-neutron-emission mass distributions for reaction MeV. The mass distributions at unmeasured energies are also展开更多
基金supported by the State Key Development Program for Basic Research of China (Nos. 2008CB717803, 2009GB107001, and2007CB209903)the Research Fund for the Doctoral Program of Higher Education of China (No. 200610011023)
文摘An attempt is made to improve the evaluation of the prompt fission neutron emis- sion from 233U（n, f） reaction for incident neutron energies below 6 MeV. The multi-modal fission approach is applied to the improved version of Los Alamos model and the point by point model. The prompt fission neutron spectra and the prompt fission neutron as a function of fragment mass （usually named ＂sawtooth＂ data） v（A） are calculated independently for the three most dominant fission modes （standard I, standard II and superlong）, and the total spectra and v（A） are syn- thesized. The multi-modal parameters are determined on the basis of experimental data of fission fragment mass distributions. The present calculation results can describe the experimental data very well, and the proposed treatment is thus a useful tool for prompt fission neutron emission prediction.
基金Major State Basic Research Development Programs for Basic Research of China(2007CB209903,2008CB717803)Research Fund for Doctoral Programof Higher Education of China(200610001023)National Found for Fostering Talents of Basic Science of China(J0630311)~~
基金Supported by Guangxi University Science and Technology Research Projects under Grant No.2013ZD007Guangxi Natural Science Foundation under Grant No.2012GXNSFAA053008+1 种基金National Natural Science Foundation of China under Grant No.11265004the Th-based Molten Salt Reactor Power System of the Strategic Pioneer Science and Technology Projects from the Chinese Academy of Sciences
文摘The pre-neutron-emission mass distributions for reaction232Th(n, f) up to 60 MeV are systematically studied with an empirical fission potential model. The energy dependences of the peaks and valleys of the pre-neutronemission mass distributions are described by the exponential expressions based on the newly measured data. The energy dependence of evaporation neutrons before scission, which plays a crucial role for the reasonable description of the mass distribution, is also considered. Both the double-humped and triple-humped shape of the measured pre-neutronemission mass distributions for reaction232Th(n, f) are reasonably well reproduced at incident energies up to 60 MeV.The mass distributions at unmeasured energies and the critical energies at which the humped pre-neutron-emission mass distributions are transformed into each other are also predicted.
基金supported by the National Natural Science Foundation of China(No.21327801)
文摘Knowledge of actinides(n,f) fission process induced by neutron is of importance in the field of nuclear power and nuclear engineering,especially for reactor applications.In this work,fission characteristics of^(238)U(n,f) reaction induced by D-T neutron source were simulated with Geant4 code from multiple perspectives,including the fission production yields,total nubar,kinetic energy distribution,fission neutron spectrum and cumulative γ-ray spectrum of the fission products.The simulation results agree well with the experimental nuclear reaction data(EXFOR) and evaluated nuclear data(ENDF).Mainly,this work was to examine the rationality of the parametric nuclear fission model in Geant4 and to direct our future experimental measurements for the cumulative fission yields of ^(238)U(n,f) reaction.
文摘当前新型核能利用系统及核数据评价的发展对快中子诱发^(239)Pu裂变核数据提出了更高的精度需求。本工作基于已提出并构建的Potential-driving模型,通过中子诱发^(239)Pu(n,f)裂变驱动势研究,计算了几个典型能量中子诱发^(239)Pu(n,f)反应发射中子前裂变碎片质量分布,并与实验数据进行了对比。结果显示:Potential-driving模型计算数据能够很好地与实验数据符合。将Potential-driving模型植入GEANT4程序,开展了快中子诱发^(239)Pu(n,f)反应相关的模拟研究,给出了14 Me V中子诱发^(239)Pu(n,f)反应的裂变碎片独立产额质量分布和电荷分布、累积产额质量分布和电荷分布、动能分布、裂变中子能谱以及^(239)Pu(n,f)反应裂变碎片平均总动能随入射中子能量的变化等数据,并与GEANT4程序原有的参数化裂变模型(G4Para Fission Model)模拟结果、ENDF/B-VII.1库评价数据以及实验数据进行了比较。结果显示:所发展的Potential-driving模型能很好地预测快中子诱发^(239)Pu(n,f)反应裂变产物数据,为快中子诱发^(239)Pu(n,f)反应裂变产物核数据的研究提供了一种更可靠的计算方法。
基金Supported by State Key Development Program for Basic Research of China (2008CB717803,2009GB107001,2007CB209903)Research Fund for the Doctoral Program of Higher Education of China (200610011023)
文摘Properties of prompt fission neutrons from 238U（n, f） are calculated for incident neutron egies below 6 MeV using the multi-modal model, including the prompt fission neutron spectrum, thnere average prompt fission neutron multiplicity, and the prompt fission neutron multiplicity as a function of the fission fragment mass v（A） （usually named ＂sawtooth＂ data） The three most dominant fission modes are taken into account. The model parameters are determined on the basis of experimental fission fragment data. The predicted results are in good agreement with the experimental data.
基金Supported by National Natural Science Foundation of China(11205246,91126010,91226102)
文摘The prompt fission neutron spectra for the neutron-induced fission of 233U for low energy neutrons （below 6 MeV） are calculated using nuclear evaporation theory with a semi-empirical method, in which the partition of the total excitation energy between the fission fragments for the nth＋233U fission reactions is determined by the available experimental and evaluation data. The calculated prompt fission neutron spectra agree well with the experimental data. The proportions of high-energy neutrons of prompt fission neutron spectrum versus incident neutron energies are investigated with the theoretical spectra, and the results are consistent with the systematics. The semi-empirical method could be a useful tool for the prompt evaluation of fission neutron spectra.
基金Supported by National Natural Science Foundation of China(11205246,91126010,U1230127,91226102)AEA CRP(15905)Defense Industrial Technology Development Program(B0120110034)
文摘Calculations of prompt fission neutron spectra （PFNS） from the ^235U（n, f） reaction were performed with a semi-empirical method for En = 7.0 and 14.7 MeV neutron energies. The total PFNS were obtained as a superposition of （n,xnf） pre-fission neutron spectra and post-fission spectra of neutrons which were evaporated from fission fragments, and these two kinds of spectra were taken as an expression of the evaporation spectrum. The contributions of （n,xnf） fission neutron spectra on the calculated PFNS were discussed. The results show that emission of one or two neutrons in the （n,nf） or （n,2nf） reactions influences the PFNS shape, and the neutron spectra of the （n,xnf） fission-channel are soft compared with the neutron spectra of the （n,f） fission channel. In addition, analysis of the multiple-chance fission component showed that second-chance fission dominates the PFNS with an incident neutron energy of 14.7 MeV whereas first-chance fission dominates the 7 MeV case.
基金Supported by the National Natural Science Foundation of China(12075008)the Key Laboratory of Nuclear Data foundation(6142A08200103)+1 种基金the Basic and Applied Basic Research Foundation of Guangdong Province,China(2021B1515120027)the State Key Laboratory of Nuclear Physics and Technology,Peking University(NPT2021KFJ57)。
文摘Accurate cross sections of neutron induced fission reactions are required in the design of advanced nuclear systems and the development of fission theory.Time projection chambers(TPCs),with their track reconstruction and particle identification capabilities,are considered the best detectors for high-precision fission cross section measurements.The TPC developed by the back-streaming white neutron source(Back-n)team of the China Spallation Neutron Source(CSNS)was used as the fission fragment detector in measurements.In this study,the cross sections of the ^(232)Th(n,f)reaction at five neutron energies in the 4.50−5.40 MeV region were measured.The fission fragments and α particles were well identified using our TPC,which led to a higher detection efficiency of the fission fragments and smaller uncertainty of the measured cross sections.Ours is the first measurement of the ^(232)Th(n,f)reaction using a TPC for the detection of fission fragments.With uncertainties less than 5%,our cross sections are consistent with the data in different evaluation libraries,including JENDL-4.0,ROSFOND-2010,CENDL-3.2,ENDF/B-VⅢ.0,and BROND-3.1,whose uncertainties can be reduced after future improvement of the measurement.
基金Supported by Guangxi University Science and Technology Research Projects(2013ZD007)Guangxi Natural Science Foundation(2012GXNSFAA053008)National Natural Science Foundation of China(11265004)
文摘Abstract： The pre-neutron-emission mass distributions for reaction ^238U（n, f） up to 60 MeV are systematically studied with an empirical fission potential model. The energy dependence of the peaks and valleys of the pre-neutronemission mass distributions is described by an exponential form based on the newly measured data. The energy dependence of evaporation neutrons before scission is also considered, which plays a crucial role in the reasonable description of the mass distributions. The measured ^238U（n, f） are reasonably well reproduced up to 60 predicted using this approach. data of the pre-neutron-emission mass distributions for reaction MeV. The mass distributions at unmeasured energies are also
