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
We numerically study a one-dimensional,nonlinear lattice model which in the linear limit is relevant to the study of bending(flexural)waves.In contrast with the classic one-dimensional mass-spring system,the linear di...We numerically study a one-dimensional,nonlinear lattice model which in the linear limit is relevant to the study of bending(flexural)waves.In contrast with the classic one-dimensional mass-spring system,the linear dispersion relation of the considered model has different characteristics in the low frequency limit.By introducing disorder in the masses of the lattice particles,we investigate how different nonlinearities in the potential(cubic,quadratic,and their combination)lead to energy delocalization,equipartition,and chaotic dynamics.We excite the lattice using single site initial momentum excitations corresponding to a strongly localized linear mode and increase the initial energy of excitation.Beyond a certain energy threshold,when the cubic nonlinearity is present,the system is found to reach energy equipartition and total delocalization.On the other hand,when only the quartic nonlinearity is activated,the system remains localized and away from equipartition at least for the energies and evolution times considered here.However,for large enough energies for all types of nonlinearities we observe chaos.This chaotic behavior is combined with energy delocalization when cubic nonlinearities are present,while the appearance of only quadratic nonlinearity leads to energy localization.Our results reveal a rich dynamical behavior and show differences with the relevant Fermi–Pasta–Ulam–Tsingou model.Our findings pave the way for the study of models relevant to bending(flexural)waves in the presence of nonlinearity and disorder,anticipating different energy transport behaviors.展开更多
We calculate the three-dimensional potential energy surface(PES)for the fission of the compound nucleus^(236)U using covariant density functional theory with constraints on the axial quadrupole and octupole deformatio...We calculate the three-dimensional potential energy surface(PES)for the fission of the compound nucleus^(236)U using covariant density functional theory with constraints on the axial quadrupole and octupole deformations(β_(2),β_(3))coexistence of the elongated and compact fission modes is predicted for comes shallow across a large range of quadrupole and octupole deformations for small scission line in the(β_(2),β_(3))plane extends to a shallow band,leading to fluctuations of several to ten MeV in the estimated total kinetic energies and of several to approximately ten nucleons in the fragment masses.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
Fission properties of the actinide nuclei are deduced from theoretical analysis.We investigate potential energy surfaces and fission barriers and predict the fission fragment mass yields of actinide isotopes.The resul...Fission properties of the actinide nuclei are deduced from theoretical analysis.We investigate potential energy surfaces and fission barriers and predict the fission fragment mass yields of actinide isotopes.The results are compared with experimental data where available.The calculations were performed in the macroscopic-microscopic approximation With the Lublin-Strasbourg Drop(LSD)for the macroscopic part,and the microscopic energy corrections were evaluated in the Yukawa-folded potential.The Fourier nuclear shape parametrization is used to describe the nuclear shape,including the non-axial degree of freedom.The fission fragment mass yields of the nuclei considered are evaluated within a 3D colletive model using the Borm-Oppenheimer approximation.展开更多
The influence of the neck parameter on the fission dynamics at low excitation energy is studied based on the three-dimensional Langevin approach,in which the nuclear shape is described with the two-center shell model(...The influence of the neck parameter on the fission dynamics at low excitation energy is studied based on the three-dimensional Langevin approach,in which the nuclear shape is described with the two-center shell model(TCSM)parametrization,and the elongation,mass asymmetry,and fragment deformation are set to be the generalized coordinates of the Langevin equation.We first study the influence of the neck parameter on the scission configuration.We find that there is almost no obvious correlation between the neck parameter and mass asymmetryηat the scission point,indicating that has no evident impact on the fragment mass distribution.The elongation Z_(0)=R_(0) and its correlation with the mass asymmetryηat the scission point are clearly influenced by the neck parameter,which has a strong effect on the total kinetic energy(TKE)distribution of the fragments.The pre-neutron emission fragment mass distributions for 14 MeV n+^(233;235;238)U and^(239)Pu are calculated,and then,based on these results,the post-neutron emission fragment mass distributions are obtained by using the experimental data of prompt neutron emission.The calculated post-neutron emission fragment mass distributions can reproduce the experimental data well.The TKE distributions for 14 MeV n+^(235)U fission are calculated for ε=0.25,0.35,and 0.45,and the results show that the TKE distribution cannot be described very well for the three cases.However,the trend of the calculated TKE distribution withεis just as expected from the scission configuration calculations.The results with ε=0.35 present a better agreement with the experiment data compared with the other two cases.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
We investigate many-body correlations caused by two- and three-body (2-, 3bd) forces. Shell-model effective interactions derived from ab initio methods (coupled-cluster method, no-core shell model) are adopted. Vl...We investigate many-body correlations caused by two- and three-body (2-, 3bd) forces. Shell-model effective interactions derived from ab initio methods (coupled-cluster method, no-core shell model) are adopted. Vlow-k potentials, based on many-body perturbation theory, are also tested, especially for their cut-off dependence. We compare the central, tensor and spin-orbit interactions from microscopic theory to the fitted interactions. After the inclusion of the three-body force, the matrix elements become fairly close to those fitted directly to experimental data. Calculations of neutron-rich oxygen isotopes are performed, to clarify the effects of 3bd forces, tensor, and spin-orbit interactions on the nuclear binding and excitation energies. We find that the 3bd force can influence the binding energies greatly, which also determines the drip line position, while its effect on excitation energies is not very pronounced. The spin-orbit force, which is part of the 2bd force, can affect the shell structure explicitly, at least for neutron-rich systems.展开更多
We have calculated the potential energy surfaces for ^(240)Pu up to the scission point using the density functional theory with different pairing strengths to investigate the effect of pairing correlations on its fiss...We have calculated the potential energy surfaces for ^(240)Pu up to the scission point using the density functional theory with different pairing strengths to investigate the effect of pairing correlations on its fission properties.An enhancement in the pairing correlations lowers the barrier heights,isomeric state,and ridge between the symmetric and asymmetric fission valleys significantly.Moreover,it weakens the microscopic shell structure around the Fermi surface,shrinks the scission frontiers,especially for the symmetric and very asymmetric fission regions,and lifts the total kinetic energies(TKEs)for the symmetric fission region.It is also emphasized that the microscopic calculation qualitatively reproduces the trend of the distribution of the measured TKEs,especially for the positions of the peaks at A_(frag)≈132 and A_(frag)≈108.展开更多
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.
基金Supported by National Natural Science Foundation of China(11790325,11790320,11790321,11961131010,U1732138,11505056,11605054,U2067205,12105369,12047568,12147219)the Continuous Basic Scientific Research Project(WDJC-2019-09)。
文摘We numerically study a one-dimensional,nonlinear lattice model which in the linear limit is relevant to the study of bending(flexural)waves.In contrast with the classic one-dimensional mass-spring system,the linear dispersion relation of the considered model has different characteristics in the low frequency limit.By introducing disorder in the masses of the lattice particles,we investigate how different nonlinearities in the potential(cubic,quadratic,and their combination)lead to energy delocalization,equipartition,and chaotic dynamics.We excite the lattice using single site initial momentum excitations corresponding to a strongly localized linear mode and increase the initial energy of excitation.Beyond a certain energy threshold,when the cubic nonlinearity is present,the system is found to reach energy equipartition and total delocalization.On the other hand,when only the quartic nonlinearity is activated,the system remains localized and away from equipartition at least for the energies and evolution times considered here.However,for large enough energies for all types of nonlinearities we observe chaos.This chaotic behavior is combined with energy delocalization when cubic nonlinearities are present,while the appearance of only quadratic nonlinearity leads to energy localization.Our results reveal a rich dynamical behavior and show differences with the relevant Fermi–Pasta–Ulam–Tsingou model.Our findings pave the way for the study of models relevant to bending(flexural)waves in the presence of nonlinearity and disorder,anticipating different energy transport behaviors.
基金Supported by the National Natural Science Foundation of China(11875225,11790325,11790320)the Special Fund from the China Nuclear Data Center+1 种基金the Fundamental Research Funds for the Central Universitiesthe Fok Ying-Tong Education Foundation。
文摘We calculate the three-dimensional potential energy surface(PES)for the fission of the compound nucleus^(236)U using covariant density functional theory with constraints on the axial quadrupole and octupole deformations(β_(2),β_(3))coexistence of the elongated and compact fission modes is predicted for comes shallow across a large range of quadrupole and octupole deformations for small scission line in the(β_(2),β_(3))plane extends to a shallow band,leading to fluctuations of several to ten MeV in the estimated total kinetic energies and of several to approximately ten nucleons in the fragment masses.
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.
基金the Polish National Science Center(2018/30/Q/ST2/00185)the National Natural Science Foundaion of China(11961131010,11790325)。
文摘Fission properties of the actinide nuclei are deduced from theoretical analysis.We investigate potential energy surfaces and fission barriers and predict the fission fragment mass yields of actinide isotopes.The results are compared with experimental data where available.The calculations were performed in the macroscopic-microscopic approximation With the Lublin-Strasbourg Drop(LSD)for the macroscopic part,and the microscopic energy corrections were evaluated in the Yukawa-folded potential.The Fourier nuclear shape parametrization is used to describe the nuclear shape,including the non-axial degree of freedom.The fission fragment mass yields of the nuclei considered are evaluated within a 3D colletive model using the Borm-Oppenheimer approximation.
基金Supported by the National Natural Science Foundation of China(12105369,11790324,11790325,11790323,11790320)the Continuous Basic Scientific Research Project(WDJC-2019-09)。
文摘The influence of the neck parameter on the fission dynamics at low excitation energy is studied based on the three-dimensional Langevin approach,in which the nuclear shape is described with the two-center shell model(TCSM)parametrization,and the elongation,mass asymmetry,and fragment deformation are set to be the generalized coordinates of the Langevin equation.We first study the influence of the neck parameter on the scission configuration.We find that there is almost no obvious correlation between the neck parameter and mass asymmetryηat the scission point,indicating that has no evident impact on the fragment mass distribution.The elongation Z_(0)=R_(0) and its correlation with the mass asymmetryηat the scission point are clearly influenced by the neck parameter,which has a strong effect on the total kinetic energy(TKE)distribution of the fragments.The pre-neutron emission fragment mass distributions for 14 MeV n+^(233;235;238)U and^(239)Pu are calculated,and then,based on these results,the post-neutron emission fragment mass distributions are obtained by using the experimental data of prompt neutron emission.The calculated post-neutron emission fragment mass distributions can reproduce the experimental data well.The TKE distributions for 14 MeV n+^(235)U fission are calculated for ε=0.25,0.35,and 0.45,and the results show that the TKE distribution cannot be described very well for the three cases.However,the trend of the calculated TKE distribution withεis just as expected from the scission configuration calculations.The results with ε=0.35 present a better agreement with the experiment data compared with the other two cases.
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Supported by National Natural Science Foundation of China(11505056,U1732138,11605054,11790325,11305108,11575290,11675148,11747312,11775316)the Outstanding Young Talent Research Fund of Zhengzhou University(1521317002)
文摘We investigate many-body correlations caused by two- and three-body (2-, 3bd) forces. Shell-model effective interactions derived from ab initio methods (coupled-cluster method, no-core shell model) are adopted. Vlow-k potentials, based on many-body perturbation theory, are also tested, especially for their cut-off dependence. We compare the central, tensor and spin-orbit interactions from microscopic theory to the fitted interactions. After the inclusion of the three-body force, the matrix elements become fairly close to those fitted directly to experimental data. Calculations of neutron-rich oxygen isotopes are performed, to clarify the effects of 3bd forces, tensor, and spin-orbit interactions on the nuclear binding and excitation energies. We find that the 3bd force can influence the binding energies greatly, which also determines the drip line position, while its effect on excitation energies is not very pronounced. The spin-orbit force, which is part of the 2bd force, can affect the shell structure explicitly, at least for neutron-rich systems.
基金Supported by National Natural Science Foundation of China (11790325, 11790320, 11790321, 11961131010, U1732138, 11505056, 11605054, U2067205,12105369, 12047568, 12147219)the Continuous Basic Scientific Research Project (WDJC-2019-09)
文摘We have calculated the potential energy surfaces for ^(240)Pu up to the scission point using the density functional theory with different pairing strengths to investigate the effect of pairing correlations on its fission properties.An enhancement in the pairing correlations lowers the barrier heights,isomeric state,and ridge between the symmetric and asymmetric fission valleys significantly.Moreover,it weakens the microscopic shell structure around the Fermi surface,shrinks the scission frontiers,especially for the symmetric and very asymmetric fission regions,and lifts the total kinetic energies(TKEs)for the symmetric fission region.It is also emphasized that the microscopic calculation qualitatively reproduces the trend of the distribution of the measured TKEs,especially for the positions of the peaks at A_(frag)≈132 and A_(frag)≈108.