We applied the four dimensional Langevin dynamical model to investigate the average spin of fission fragments. Elongation, neck thickness, asymmetry parameter, and the orientation degree of freedom（K coordinate）are ...We applied the four dimensional Langevin dynamical model to investigate the average spin of fission fragments. Elongation, neck thickness, asymmetry parameter, and the orientation degree of freedom（K coordinate）are the four dimensions of the dynamical model. We assume that the collective modes depend on the emission angle of the fragments, then different parameters related to the average spin of fission fragments are calculated dynamically.The angle dependence of average spin of fission fragments is investigated by calculating the spin at angles 90？and165？. Also, the obtained results based on the transition state model at scission point are presented. One can obtain better agreement between the results of the dynamical model and experimental data in comparison with the results of the transition state model.展开更多
According to some experimental and evaluated data,the total excitation energy partitioning way between both of the fission fragments was given with a semi-empirical method. With the calculated energy partitioning way,...According to some experimental and evaluated data,the total excitation energy partitioning way between both of the fission fragments was given with a semi-empirical method. With the calculated energy partitioning way,the prompt neutron multiplicity as a function of fragment mass,（A） ,for neutron-induced fission of 235U at En=0.0253 eV,3 MeV,and 5 MeV was calculated. The results are checked with the total average prompt neutron multiplicities and compared with the experimental and evaluated data.展开更多
The fission fragment mass-yields are evaluated for pre-actinide and actinide isotopes using a systematic statistical scission point model.The total potential energy of the fissioning systems at the scission point is p...The fission fragment mass-yields are evaluated for pre-actinide and actinide isotopes using a systematic statistical scission point model.The total potential energy of the fissioning systems at the scission point is presented in approximate relations as functions of mass numbers,deformation parameters and the temperature of complementary fission fragments.The collective temperature,Tcoll,and the temperature of fission fragments,Ti,are separated and the effect of collective temperature on mass yields results is investigated.The fragment temperature has been calculated with the generalized superfluid model.The sum of deformation parameters of complementary fission fragments has been obtained by fitting the calculated results with the experimental data.To investigate the transitions between symmetric and asymmetric modes mass yields for pre-actinide and heavy actinides are calculated with this model.The transition from asymmetric to symmetric fission is well reproduced using this systematic statistical scission point model.The calculated results are in good agreement with the experimental data with Tcoll=2 Me V at intermediate excitation energy and with T_(coll)=1MeV for spontaneous fission.Despite the Langevin model,in the scission point model,a constraint on the deformation parameters of fission fragments has little effect on the results of the mass yield.展开更多
An experiment for measuring the hyperon-related fission rate was carried out with the reaction 209^Bi（e, e＇K^＋）209^hPb at the Thomas Jefferson National Laboratory （Jlab）. In the experiment, the performance of th...An experiment for measuring the hyperon-related fission rate was carried out with the reaction 209^Bi（e, e＇K^＋）209^hPb at the Thomas Jefferson National Laboratory （Jlab）. In the experiment, the performance of the fission fragment detector （FFD） was dramaticlly crashed by the background particles in comparison with that during the test without beam. The scattering of the high intensity （500 nA） primary electrons was the dominant cause. Using the GEANT4 toolkit, this report simulates the experimental situation of the target chamber in which the FFD was located. The simulation results indicate that the background particles were dominantly （~ electrons, and protons and alpha particles were the important heavy background particles. The performance of the multi-wire proportional chambers （MWPCs） depends not only on the background-particle intensity but also the current density, which was also given by the simulation code. Furthermore, the measures to suppress the background particles were also investigated with the simulation code.展开更多
MIXED Oxide Nuclear fuel (MOX) contains both uranium and plutonium in oxidized form. It is important to calculate the nuclear decay heat due to the single thermal fission (fission due to 0.0235 eV neutron) for all fis...MIXED Oxide Nuclear fuel (MOX) contains both uranium and plutonium in oxidized form. It is important to calculate the nuclear decay heat due to the single thermal fission (fission due to 0.0235 eV neutron) for all fissile nuclei in the MOX fuels (U<sup>235</sup>, Pu<sup>239</sup>, and Pu<sup>241</sup>). These fissile nuclei are the main source of the decay heat in MOX fuel. Decay heat calculation of the weighted fissile material content in MOX fuel is also important. A numerical method was used in this work to calculate the concentrations of all fission products due to the individual thermal fission of the three fissile materials as a function of time N(t). The decay heat calculations for the three fissile materials are directly calculated using the summation method by knowing the different concentrations of fission products over time. The average decay heat of the MOX fuel in induced thermal fission is also concluded. The most influential nuclei in the decay heat were also identified. The method used has been validated by several comparisons before, but the new in this work is using the most recent Evaluated Nuclear Data Library ENDF/B-VIII.0. Calculations of decay heat show very common trends for a period of 10<sup>7</sup> sec after the fission burst of thermal fissions of individual fissile nuclei. Moreover, the code showed high capability in calculating the fission fragments inventories and decay heats due to the decay of fission fragments of 31 fissionable nuclei.展开更多
In this paper, a home-made code was designed to calculate the decay heat emitted by fission fragments as a result of successive radioactive emissions after a fission burst. The nuclear data necessary for the calculati...In this paper, a home-made code was designed to calculate the decay heat emitted by fission fragments as a result of successive radioactive emissions after a fission burst. The nuclear data necessary for the calculations was extracted from the latest version of the Evaluated Nuclear Data Library ENDF/B-VIII.0. The code can calculate the decay heat of thermal and fast neutron-induced fission reactions on the isotopes of Thorium, Protactinium, Uranium, Neptunium, Plutonium, Americium, Curium, California, Einsteinium, and Fermium. A numerical method was used in this work to calculate the decay heat of all fission fragments due to the individual thermal or fast fissions of the isotopes of the previous ten actinides. The most influential nuclei in the decay heat were also identified at different times after the fission event. Moreover, the code showed high capability in calculating the fission fragments inventories and decay heats due to the decay of fission fragments of 31 fissionable nuclei.展开更多
Using the Skyrme density functional theory,potential energy surfaces of^(240)Pu with constraints on the axial quadrupole and octupole deformations(q_(20)and q_(30))were calculated.The volume-like and surface-like pair...Using the Skyrme density functional theory,potential energy surfaces of^(240)Pu with constraints on the axial quadrupole and octupole deformations(q_(20)and q_(30))were calculated.The volume-like and surface-like pairing forces,as well as a combination of these two forces,were used for the Hartree–Fock–Bogoliubov approximation.Variations in the least-energy fission path,fission barrier,pairing energy,total kinetic energy,scission line,and mass distribution of the fission fragments based on the different forms of the pairing forces were analyzed and discussed.The fission dynamics were studied based on the timedependent generator coordinate method plus the Gaussian overlap approximation.The results demonstrated a sensitivity of the mass and charge distributions of the fission fragments on the form of the pairing force.Based on the investigation of the neutron-induced fission of^(239)Pu,among the volume,mixed,and surface pairing forces,the mixed pairing force presented a good reproduction of the experimental data.展开更多
The mean total kinetic energy as a function of fission fragments,the<TKE>distribution,is presented for neutron-induced fission of ^(235-239)Np using the scission point model.The calculated results of<TKE>f...The mean total kinetic energy as a function of fission fragments,the<TKE>distribution,is presented for neutron-induced fission of ^(235-239)Np using the scission point model.The calculated results of<TKE>for neutron-induced fission of ^(237,238) Np are compared with the available experimental data to obtain the deformation parameters in the scission point model.The deformation parameters of fission fragments are discussed at the scission point.The calculated results are also compared with the results from other methods and with experimental data.The behavior of the<TKE>distribution is then studied for the neutron-induced fission of actinides.This indicates that the<TKE>values for neutron-induced fission of actinides with odd mass numbers are greater than for those with even mass numbers.展开更多
The temperature dependent width of the fission fragment distributions was simulated in the Langevin equation by taking two-parameter exponential form of the fission fragment mass variance at scission point for each fi...The temperature dependent width of the fission fragment distributions was simulated in the Langevin equation by taking two-parameter exponential form of the fission fragment mass variance at scission point for each fission event. The result can reproduce experimental data well, and it permits to make reliable estimate for unmeasured product yields near symmetry fission.展开更多
To study the neutron-induced fission of^(239)Pu,potential energy surface(PES)calculations were performed using zero and finite-temperature density functional theory(FT-DFT)with the Skyrme force.The energy of the incid...To study the neutron-induced fission of^(239)Pu,potential energy surface(PES)calculations were performed using zero and finite-temperature density functional theory(FT-DFT)with the Skyrme force.The energy of the incident neutron was simulated by the temperature of the FT-DFT.The variations of the least-energy fission path,fission barrier,total kinetic energy,scission line,and mass distribution of fission fragments with the incident neutron energy were analyzed.It was learned that an increase in the temperature lowers the barrier height,the isomericstate energy,and the ridge between symmetric and asymmetric fission valleys.Additionally,the gaps of the single particle levels become smaller with an increase in the temperature.As the temperature increases,the pre-fission region shrinks,and the scission occurs at smaller deformation around the symmetric fission channel.At low temperatures,the pairing correlations in the collective space are similar to those in zero-temperature DFT,and when the temperature is T>0.3 MeV,the pairing gaps decrease rapidly.Two different methods were used to calculate the fission yields of the neutron-induced fision^(239)Pu(n,)with different incident neutron energies,in the framework of timedependent generator coordinate method(TDGCM).One way to calculate the fission yield of^(239)Pu(n,f)is to solve the collective equation of the TDGCM by using the PES from the FT-DFT with the corresponding temperature.The other involves using the PES from the zero-temperature DFT and adjusting the initial collective energy of the wave packet in the TDGCM according to the incident neutron energy.For the cases of the lower incident neutron energies,these two methods gave similar results and reproduced the experimental peak and width of fission fragment distribution.However,for the highest incident neutron energy considered in this study,the results from the TDGCM using the PES from zero-temperature DFT deviated explicitly from the experimental data,whereas those obtained by using the PES from FT-DFT remained close to the experimental data.This indicated that,with the increase in the incident neutron energy,the shell structure of the compound nuclei changed explicitly;thus,it may not be effective to use the PES from zero-temperature to perform the fission dynamic calculation.展开更多
Based on the neutron induced fission fragment mass distribution data up to neutron energy 20 MeV measured with the double kinetic energy method （KEM） and the radio active method （RAM）, the systematics of fission f...Based on the neutron induced fission fragment mass distribution data up to neutron energy 20 MeV measured with the double kinetic energy method （KEM） and the radio active method （RAM）, the systematics of fission fragment mass distribution was investigated by using 5 Gaussian model and the systematics parameters were obtained by fitting the experimental data. With the systematics, the yields of any mass A and at any energy in the region from 0 to 20 MeV of neutron energy can be calculated. The calculated results could well reproduce the experimental data measured with KEM, but show some systematical deviation from the data measured by RAM, which reflects some systematical deviations between the two kinds of measured data. The error of systematics yield was calculated in an exact error transformation way, including from the error of the experimental yield data to the error of the discrete parameters, then to the systematics parameters, and at last to the yield calculated with systematics.展开更多
The prompt fission neutron spectra for the neutron-induced fission of 235U at En 5 MeV are calculated using nuclear evaporation theory with a semi-empirical model, in which the nonconstant and con- stant temperatures ...The prompt fission neutron spectra for the neutron-induced fission of 235U at En 5 MeV are calculated using nuclear evaporation theory with a semi-empirical model, in which the nonconstant and con- stant temperatures related to the Fermi gas model are taken into account. The calculated prompt fission neutron spectra reproduce the experimental data well. For the n（thermal）＋235 U reaction, the average nuclear temperature of the fission fragment, and the probability distribution of the nuclear temperature, are discussed and compared with the Los Alamos model. The energy carried away by γ rays emitted from each fragment is also obtained and the results are in good agreement with the existing experimental data.展开更多
When a A hyperon is embedded in a nucleus it can form a hypernucleus. The lifetime and its mass dependence of stable hypernuclei provide information about the AN interaction in the nuclear medium. This work will intro...When a A hyperon is embedded in a nucleus it can form a hypernucleus. The lifetime and its mass dependence of stable hypernuclei provide information about the AN interaction in the nuclear medium. This work will introduce the Jefferson Lab experiment （E02-017）, which aims to study the lifetime of the heavy hypernuclei using a specially developed fission fragment detection technique： a multi-wire proportional chamber operating under low gas pressure （LPMWPC）. The trajectory of the detected fragment is reconstructed and used to find the fission point on the target foil, the position resolution is less than I ram, which meets the original design, the separation of target materials and events mixture percentage in different regions are verified by Monte Carlo simulation.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
Two couples of low pressure multi-wire proportional chambers （MWPC） were located in the target chamber to detect fission fragments in a hypernuclei producing experiment at Thomas Jefferson National Laboratory （Jlab...Two couples of low pressure multi-wire proportional chambers （MWPC） were located in the target chamber to detect fission fragments in a hypernuclei producing experiment at Thomas Jefferson National Laboratory （Jlab）. In the experiment, a continuous wave （CW） electron beam was applied to form hypernuclei by electromagnetic interaction. In the target chamber, the high energy （1.853 GeV） and high intensity （500 nA） primary electron beam caused a high particle background, which influenced the detection of the fission fragments. This report described the design of the MWPCs and studied the fission-fragment detecting performance of them under such a high background. The efficiency of the MWPCs was given with the help of a high resolution kaon spectrometer. At the same time, the background particles were discussed with a Monte Carlo code based on GEANT4.展开更多
The isoscaling parameters aevai in the fissioning systems,i.e.,those extracted from the Evaluated Nuclear Data Library(ENDF/B-VIII.O)and the Joint Evaluated Fission and Fusion File(JEFF-3.3),show an obvious difference...The isoscaling parameters aevai in the fissioning systems,i.e.,those extracted from the Evaluated Nuclear Data Library(ENDF/B-VIII.O)and the Joint Evaluated Fission and Fusion File(JEFF-3.3),show an obvious difference from simple statistic model prediction where only the symmetry energy plays the dominant role.To explain the aeVai as a function of the charge number of the fission fragment,a statistic scission point model is adopted.Our analysis shows that the effects of the shell correction,nuclear shape deformation,and intrinsic temperature of fission fragments are indispensable as well as the symmetry energy.Furthermore,an alternative method for extracting the intrinsic temperatures of fission fragments is proposed based on the isoscaling relationship in fission fragments.The intrinsic temperatures of the light fragments are higher than those of the heavy fragments.展开更多
Purpose Back-n is a white neutron beamline at China spallation neutron source,which was established in the year of 2018.It is a powerful facility for nuclear data measurement,neutron detector calibration,and radiation...Purpose Back-n is a white neutron beamline at China spallation neutron source,which was established in the year of 2018.It is a powerful facility for nuclear data measurement,neutron detector calibration,and radiation effect research.Method A series of detectors were built for different experiments,including beam monitoring,beam profile measurement,neutron induced secondaries(fission fragments,light charged particles and gamma)cross section measurement,and neutron resonance radiography,etc.A common digitization electronics and a cluster-based DAQ were developed for these detector systems.Most detectors have been employed at Back-n and serviced for experiments from the beginning of the beamline running.Results and conclusion As an overview of detectors of Back-n,the details of the detector design and the experiment performing are described in this paper.Some developing systems,e.g.,MTPC and B-MCP,are also included.展开更多
For the n＋235U fission reaction, the total excitation energy partition of the fission fragments, the average neutron kinetic energy ε （A） and the total average energies Eˉγ（A） removed by γ rays as a function ...For the n＋235U fission reaction, the total excitation energy partition of the fission fragments, the average neutron kinetic energy ε （A） and the total average energies Eˉγ（A） removed by γ rays as a function of fission fragment mass are given at incident energies up to 20 MeV. The prompt neutron multiplicity as a function of the fragment mass, ν（A）, for neutron-induced fission of 235U at different incident neutron energies is calculated. The calculated results are checked with the total average prompt neutron multiplicities νˉ and compared with the experimental and evaluated data. Some prompt neutron and γ emission mechanisms are discussed.展开更多
文摘We applied the four dimensional Langevin dynamical model to investigate the average spin of fission fragments. Elongation, neck thickness, asymmetry parameter, and the orientation degree of freedom（K coordinate）are the four dimensions of the dynamical model. We assume that the collective modes depend on the emission angle of the fragments, then different parameters related to the average spin of fission fragments are calculated dynamically.The angle dependence of average spin of fission fragments is investigated by calculating the spin at angles 90？and165？. Also, the obtained results based on the transition state model at scission point are presented. One can obtain better agreement between the results of the dynamical model and experimental data in comparison with the results of the transition state model.
文摘According to some experimental and evaluated data,the total excitation energy partitioning way between both of the fission fragments was given with a semi-empirical method. With the calculated energy partitioning way,the prompt neutron multiplicity as a function of fragment mass,（A） ,for neutron-induced fission of 235U at En=0.0253 eV,3 MeV,and 5 MeV was calculated. The results are checked with the total average prompt neutron multiplicities and compared with the experimental and evaluated data.
文摘The fission fragment mass-yields are evaluated for pre-actinide and actinide isotopes using a systematic statistical scission point model.The total potential energy of the fissioning systems at the scission point is presented in approximate relations as functions of mass numbers,deformation parameters and the temperature of complementary fission fragments.The collective temperature,Tcoll,and the temperature of fission fragments,Ti,are separated and the effect of collective temperature on mass yields results is investigated.The fragment temperature has been calculated with the generalized superfluid model.The sum of deformation parameters of complementary fission fragments has been obtained by fitting the calculated results with the experimental data.To investigate the transitions between symmetric and asymmetric modes mass yields for pre-actinide and heavy actinides are calculated with this model.The transition from asymmetric to symmetric fission is well reproduced using this systematic statistical scission point model.The calculated results are in good agreement with the experimental data with Tcoll=2 Me V at intermediate excitation energy and with T_(coll)=1MeV for spontaneous fission.Despite the Langevin model,in the scission point model,a constraint on the deformation parameters of fission fragments has little effect on the results of the mass yield.
基金supported by the Fundamental Research Funds for the Central Universities of China (No.HEUCF101501)the Fundamental Research Funds of Harbin Engineering University of China (No.002150260713)
文摘An experiment for measuring the hyperon-related fission rate was carried out with the reaction 209^Bi（e, e＇K^＋）209^hPb at the Thomas Jefferson National Laboratory （Jlab）. In the experiment, the performance of the fission fragment detector （FFD） was dramaticlly crashed by the background particles in comparison with that during the test without beam. The scattering of the high intensity （500 nA） primary electrons was the dominant cause. Using the GEANT4 toolkit, this report simulates the experimental situation of the target chamber in which the FFD was located. The simulation results indicate that the background particles were dominantly （~ electrons, and protons and alpha particles were the important heavy background particles. The performance of the multi-wire proportional chambers （MWPCs） depends not only on the background-particle intensity but also the current density, which was also given by the simulation code. Furthermore, the measures to suppress the background particles were also investigated with the simulation code.
文摘MIXED Oxide Nuclear fuel (MOX) contains both uranium and plutonium in oxidized form. It is important to calculate the nuclear decay heat due to the single thermal fission (fission due to 0.0235 eV neutron) for all fissile nuclei in the MOX fuels (U<sup>235</sup>, Pu<sup>239</sup>, and Pu<sup>241</sup>). These fissile nuclei are the main source of the decay heat in MOX fuel. Decay heat calculation of the weighted fissile material content in MOX fuel is also important. A numerical method was used in this work to calculate the concentrations of all fission products due to the individual thermal fission of the three fissile materials as a function of time N(t). The decay heat calculations for the three fissile materials are directly calculated using the summation method by knowing the different concentrations of fission products over time. The average decay heat of the MOX fuel in induced thermal fission is also concluded. The most influential nuclei in the decay heat were also identified. The method used has been validated by several comparisons before, but the new in this work is using the most recent Evaluated Nuclear Data Library ENDF/B-VIII.0. Calculations of decay heat show very common trends for a period of 10<sup>7</sup> sec after the fission burst of thermal fissions of individual fissile nuclei. Moreover, the code showed high capability in calculating the fission fragments inventories and decay heats due to the decay of fission fragments of 31 fissionable nuclei.
文摘In this paper, a home-made code was designed to calculate the decay heat emitted by fission fragments as a result of successive radioactive emissions after a fission burst. The nuclear data necessary for the calculations was extracted from the latest version of the Evaluated Nuclear Data Library ENDF/B-VIII.0. The code can calculate the decay heat of thermal and fast neutron-induced fission reactions on the isotopes of Thorium, Protactinium, Uranium, Neptunium, Plutonium, Americium, Curium, California, Einsteinium, and Fermium. A numerical method was used in this work to calculate the decay heat of all fission fragments due to the individual thermal or fast fissions of the isotopes of the previous ten actinides. The most influential nuclei in the decay heat were also identified at different times after the fission event. Moreover, the code showed high capability in calculating the fission fragments inventories and decay heats due to the decay of fission fragments of 31 fissionable nuclei.
基金supported by the National Key R&D Program of China(No.2022YFA1602000)National Natural Science Foundation of China(Nos.12275081,U2067205,11790325,and U1732138)the Continuous-support Basic Scientific Research Project。
文摘Using the Skyrme density functional theory,potential energy surfaces of^(240)Pu with constraints on the axial quadrupole and octupole deformations(q_(20)and q_(30))were calculated.The volume-like and surface-like pairing forces,as well as a combination of these two forces,were used for the Hartree–Fock–Bogoliubov approximation.Variations in the least-energy fission path,fission barrier,pairing energy,total kinetic energy,scission line,and mass distribution of the fission fragments based on the different forms of the pairing forces were analyzed and discussed.The fission dynamics were studied based on the timedependent generator coordinate method plus the Gaussian overlap approximation.The results demonstrated a sensitivity of the mass and charge distributions of the fission fragments on the form of the pairing force.Based on the investigation of the neutron-induced fission of^(239)Pu,among the volume,mixed,and surface pairing forces,the mixed pairing force presented a good reproduction of the experimental data.
文摘The mean total kinetic energy as a function of fission fragments,the<TKE>distribution,is presented for neutron-induced fission of ^(235-239)Np using the scission point model.The calculated results of<TKE>for neutron-induced fission of ^(237,238) Np are compared with the available experimental data to obtain the deformation parameters in the scission point model.The deformation parameters of fission fragments are discussed at the scission point.The calculated results are also compared with the results from other methods and with experimental data.The behavior of the<TKE>distribution is then studied for the neutron-induced fission of actinides.This indicates that the<TKE>values for neutron-induced fission of actinides with odd mass numbers are greater than for those with even mass numbers.
基金Supported by Knowledge Innovation Program of Chinese Academy of Sciences (55010701)National Support Plan of Science and Technology of China (2006BAI08B04-7)+2 种基金973 Program (2007CB815004)Shanghai Development Foundation from Science and Technology (06JC14082)National Natural Science Foundation of China (10775167)
文摘The temperature dependent width of the fission fragment distributions was simulated in the Langevin equation by taking two-parameter exponential form of the fission fragment mass variance at scission point for each fission event. The result can reproduce experimental data well, and it permits to make reliable estimate for unmeasured product yields near symmetry fission.
基金Supported by the National Natural Science Foundation of China(11790325,12275081,11790320,11790321,11961131010,11605054,12105369,12147219,12047568)the Continuous Basic Scientific Research Project(WDJC-2019-09)。
文摘To study the neutron-induced fission of^(239)Pu,potential energy surface(PES)calculations were performed using zero and finite-temperature density functional theory(FT-DFT)with the Skyrme force.The energy of the incident neutron was simulated by the temperature of the FT-DFT.The variations of the least-energy fission path,fission barrier,total kinetic energy,scission line,and mass distribution of fission fragments with the incident neutron energy were analyzed.It was learned that an increase in the temperature lowers the barrier height,the isomericstate energy,and the ridge between symmetric and asymmetric fission valleys.Additionally,the gaps of the single particle levels become smaller with an increase in the temperature.As the temperature increases,the pre-fission region shrinks,and the scission occurs at smaller deformation around the symmetric fission channel.At low temperatures,the pairing correlations in the collective space are similar to those in zero-temperature DFT,and when the temperature is T>0.3 MeV,the pairing gaps decrease rapidly.Two different methods were used to calculate the fission yields of the neutron-induced fision^(239)Pu(n,)with different incident neutron energies,in the framework of timedependent generator coordinate method(TDGCM).One way to calculate the fission yield of^(239)Pu(n,f)is to solve the collective equation of the TDGCM by using the PES from the FT-DFT with the corresponding temperature.The other involves using the PES from the zero-temperature DFT and adjusting the initial collective energy of the wave packet in the TDGCM according to the incident neutron energy.For the cases of the lower incident neutron energies,these two methods gave similar results and reproduced the experimental peak and width of fission fragment distribution.However,for the highest incident neutron energy considered in this study,the results from the TDGCM using the PES from zero-temperature DFT deviated explicitly from the experimental data,whereas those obtained by using the PES from FT-DFT remained close to the experimental data.This indicated that,with the increase in the incident neutron energy,the shell structure of the compound nuclei changed explicitly;thus,it may not be effective to use the PES from zero-temperature to perform the fission dynamic calculation.
文摘Based on the neutron induced fission fragment mass distribution data up to neutron energy 20 MeV measured with the double kinetic energy method （KEM） and the radio active method （RAM）, the systematics of fission fragment mass distribution was investigated by using 5 Gaussian model and the systematics parameters were obtained by fitting the experimental data. With the systematics, the yields of any mass A and at any energy in the region from 0 to 20 MeV of neutron energy can be calculated. The calculated results could well reproduce the experimental data measured with KEM, but show some systematical deviation from the data measured by RAM, which reflects some systematical deviations between the two kinds of measured data. The error of systematics yield was calculated in an exact error transformation way, including from the error of the experimental yield data to the error of the discrete parameters, then to the systematics parameters, and at last to the yield calculated with systematics.
基金Supported by IAEA-CRP(15905)the State Key Laboratory of Nuclear Physics and Technology,Peking University(SKL-NPT)
文摘The prompt fission neutron spectra for the neutron-induced fission of 235U at En 5 MeV are calculated using nuclear evaporation theory with a semi-empirical model, in which the nonconstant and con- stant temperatures related to the Fermi gas model are taken into account. The calculated prompt fission neutron spectra reproduce the experimental data well. For the n（thermal）＋235 U reaction, the average nuclear temperature of the fission fragment, and the probability distribution of the nuclear temperature, are discussed and compared with the Los Alamos model. The energy carried away by γ rays emitted from each fragment is also obtained and the results are in good agreement with the existing experimental data.
基金Supported by National Natural Science Foundation of China(11175075,11135002 and 91026021)supported by the State Scholarship Fund Program of the China Scholarship Council
文摘When a A hyperon is embedded in a nucleus it can form a hypernucleus. The lifetime and its mass dependence of stable hypernuclei provide information about the AN interaction in the nuclear medium. This work will introduce the Jefferson Lab experiment （E02-017）, which aims to study the lifetime of the heavy hypernuclei using a specially developed fission fragment detection technique： a multi-wire proportional chamber operating under low gas pressure （LPMWPC）. The trajectory of the detected fragment is reconstructed and used to find the fission point on the target foil, the position resolution is less than I ram, which meets the original design, the separation of target materials and events mixture percentage in different regions are verified by Monte Carlo simulation.
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 Fundamental Research Funds for Central Universities (HEUCF101501)Fundamental Research Funds of Harbin Engineering University (002150260713)National Natural Science Foundation of China (10575046)
文摘Two couples of low pressure multi-wire proportional chambers （MWPC） were located in the target chamber to detect fission fragments in a hypernuclei producing experiment at Thomas Jefferson National Laboratory （Jlab）. In the experiment, a continuous wave （CW） electron beam was applied to form hypernuclei by electromagnetic interaction. In the target chamber, the high energy （1.853 GeV） and high intensity （500 nA） primary electron beam caused a high particle background, which influenced the detection of the fission fragments. This report described the design of the MWPCs and studied the fission-fragment detecting performance of them under such a high background. The efficiency of the MWPCs was given with the help of a high resolution kaon spectrometer. At the same time, the background particles were discussed with a Monte Carlo code based on GEANT4.
基金Supported by the National Natural Science Foundation of China(11790325,11875323,11875125,11947410,11705163,11790320,11790323,11961141003)the National Key R&D Program of China(2018 YFA0404404)+1 种基金the Continuous Basic Scientific Research Project(WDJC-2019-09,WDJC-2019-13,BJ20002501)of the funding of China Institute of Atomic EnergyChinese-Polish Joint project by the National Science Foundation of China(11961131010)。
文摘The isoscaling parameters aevai in the fissioning systems,i.e.,those extracted from the Evaluated Nuclear Data Library(ENDF/B-VIII.O)and the Joint Evaluated Fission and Fusion File(JEFF-3.3),show an obvious difference from simple statistic model prediction where only the symmetry energy plays the dominant role.To explain the aeVai as a function of the charge number of the fission fragment,a statistic scission point model is adopted.Our analysis shows that the effects of the shell correction,nuclear shape deformation,and intrinsic temperature of fission fragments are indispensable as well as the symmetry energy.Furthermore,an alternative method for extracting the intrinsic temperatures of fission fragments is proposed based on the isoscaling relationship in fission fragments.The intrinsic temperatures of the light fragments are higher than those of the heavy fragments.
基金support provided by the National KeyR&DProgram of China(Grant No.2016YFA0401600).
文摘Purpose Back-n is a white neutron beamline at China spallation neutron source,which was established in the year of 2018.It is a powerful facility for nuclear data measurement,neutron detector calibration,and radiation effect research.Method A series of detectors were built for different experiments,including beam monitoring,beam profile measurement,neutron induced secondaries(fission fragments,light charged particles and gamma)cross section measurement,and neutron resonance radiography,etc.A common digitization electronics and a cluster-based DAQ were developed for these detector systems.Most detectors have been employed at Back-n and serviced for experiments from the beginning of the beamline running.Results and conclusion As an overview of detectors of Back-n,the details of the detector design and the experiment performing are described in this paper.Some developing systems,e.g.,MTPC and B-MCP,are also included.
文摘For the n＋235U fission reaction, the total excitation energy partition of the fission fragments, the average neutron kinetic energy ε （A） and the total average energies Eˉγ（A） removed by γ rays as a function of fission fragment mass are given at incident energies up to 20 MeV. The prompt neutron multiplicity as a function of the fragment mass, ν（A）, for neutron-induced fission of 235U at different incident neutron energies is calculated. The calculated results are checked with the total average prompt neutron multiplicities νˉ and compared with the experimental and evaluated data. Some prompt neutron and γ emission mechanisms are discussed.
