Photofission fragments mass yield for^(232)Th,^(234;238) U,^(237) Np, and^(239;240;242) Pu isotopes are investigated.The calculations are done using a developed approach based on Gorodisskiy's phenomenological for...Photofission fragments mass yield for^(232)Th,^(234;238) U,^(237) Np, and^(239;240;242) Pu isotopes are investigated.The calculations are done using a developed approach based on Gorodisskiy's phenomenological formalism. The Gorodisskiy's method is developed to be applied for the neutron-induced fission. Here we revised it for application to photofission. The effect of emitted neutron prior to fission on the fission fragment mass yields has also been studied. The peak-to-valley ratio is extracted for the240 Pu isotope as a function of energy. Obtained results of the present formalism are compared with the available experimental data. Satisfactory agreement is achieved between the results of present approach and the experimental data.展开更多
The fission angular distributions for the <sup>16</sup>O+<sup>159</sup>Tb,<sup>16</sup>O+<sup>197</sup>Au and <sup>16</sup>O+<sup>209</sup>Bi rea...The fission angular distributions for the <sup>16</sup>O+<sup>159</sup>Tb,<sup>16</sup>O+<sup>197</sup>Au and <sup>16</sup>O+<sup>209</sup>Bi reac-tions are measured by the solid state nuclear track detectors.After subtraction of the contribu-tion of intermediate mass fragment（IMF）,the fission angular distributions are fitted by thetransitional state statistical model（TSM）and the single-spin standard theory is used to extractthe spins of the fissioning nuclei.The relation between spins and bombarding energy is dis-cussed.展开更多
The reactions of ^16O＋^204pb, ^82Se＋^138Ba and ^96Zr＋^124Sn lead to the same compound nucleus ^220Th. In terms of the assumption that the surviving probability is independent of entrance channel, we have extracted ...The reactions of ^16O＋^204pb, ^82Se＋^138Ba and ^96Zr＋^124Sn lead to the same compound nucleus ^220Th. In terms of the assumption that the surviving probability is independent of entrance channel, we have extracted the fusion hindrance factor from the evaporation residue cross sections for the reactions of ^82Se＋^138 Ba and ^96Zr＋^124Sn and compared with the results calculated using a two-parameter Smoluchowski equation. The theoretical predictions are basically in agreement with the experimental data. It is found that the probability of forming a compact ^220Th is less than 10% for the reactions considered. For the systems more massive than ^220Th, fusion should be much more strongly suppressed due to the competition of quasifission with complete fusion. Understanding of this inhibition is essential to forming new superheavy nuclei.展开更多
The lifetimes of a decays of the recently produced isotopes of the elements 112, 114, 116 and the element ^294118 and of some decay products have been calculated theoretically within the Wentzel-Kramers-Brillouin appr...The lifetimes of a decays of the recently produced isotopes of the elements 112, 114, 116 and the element ^294118 and of some decay products have been calculated theoretically within the Wentzel-Kramers-Brillouin approximation. The a decay barriers have been determined in the quasimolecular shape path within a generalized liquid drop model including the proximity effects between nuclei in a neck, the mass and charge asymmetry and the precise nuclear radius. These calculations provide reasonable estimates for the observed a decay lifetimes. The calculated results have been compared with the results of the density-dependent M3Y effective interaction and the experimental data. It is indicated that the theoretical foundation of the generalized liquid drop model is as good as that of the microscopic DDM3Y model, at least in the sense of predicting the T1/2 values as long as one uses a correct a decay energy. The half lives of these new nuclei are well tested from the consistence of the macroscopic, the microscopic and the experimental data.展开更多
A sequential decay model is used to study isoscaling, i.e. the factorization of the isotope ratios from sources of different isospins and sizes over a broad range of excitation energies, into fugacity terms of proton ...A sequential decay model is used to study isoscaling, i.e. the factorization of the isotope ratios from sources of different isospins and sizes over a broad range of excitation energies, into fugacity terms of proton and neutron number, R21（N, Z） = Y2（ N, Z）/Y1（ N, Z） = Cexp（αN -βZ）. It is found that the isoscaling parameters α and β have a strong dependence on the isospin difference of equilibrated source and excitation energy, no significant influence of the source size on α andβ has been observed. It is found that α and β decrease with the excitation energy and are linear functions of 1/T and △（Z/A）2 or△（N/A）2 of the sources. Symmetry energy coefticient Gsym is constrained from the relationship of a and source △（Z/A）2, /3 and source △（N/A）2.展开更多
Potential energy surfaces of uranium nuclei in the range of mass numbers 229 through 244 are investigated in the framework of the macroscopic-microscopic model and the heights of static fission barriers are obtained i...Potential energy surfaces of uranium nuclei in the range of mass numbers 229 through 244 are investigated in the framework of the macroscopic-microscopic model and the heights of static fission barriers are obtained in terms of a double-humped structure. The macroscopic part of the nuclear energy is calculated according to Lublin–Strasbourg-drop(LSD) model. Shell and pairing corrections as the microscopic part are calculated with a folded-Yukawa single-particle potential. The calculation is carried out in a five-dimensional parameter space of the generalized Lawrence shapes. In order to extract saddle points on the potential energy surface, a new algorithm which can effectively find an optimal fission path leading from the ground state to the scission point is developed. The comparison of our results with available experimental data and others' theoretical results confirms the reliability of our calculations.展开更多
The competition between α-decay and spontaneous fission of superheavy nuclei（SHN） is investigated by the generalized liquid drop model（GLDM） and the modified Swiatecki＇s formula respectively. The theoretical dec...The competition between α-decay and spontaneous fission of superheavy nuclei（SHN） is investigated by the generalized liquid drop model（GLDM） and the modified Swiatecki＇s formula respectively. The theoretical decay modes are in good agreement with the experimental results. Predictions are made for as-yet unobserved superheavy nuclei. The theoretical calculations show that the nuclei^298 120,^295 119,^290 118,^291 117,^287 117,^294 116,^289 116,^286 116,^285 116,^284 115,^283 115,^283 114,^282 114,^280 113,^276 112,^275 112,^274 112,^273 111,^272 110,^265 109 may be synthesized experimentally in the near future since they not only have relatively large predicted cross sections but can also be identified via α-decay chains.展开更多
Some nearly-symmetric fusion reactions are systematically investigated with the improved quantum molecular dynamics(Im QMD)model. By introducing two-body inelastic scattering in the Fermi constraint procedure, the sta...Some nearly-symmetric fusion reactions are systematically investigated with the improved quantum molecular dynamics(Im QMD)model. By introducing two-body inelastic scattering in the Fermi constraint procedure, the stability of an individual nucleus and the description of fusion cross sections at energies near the Coulomb barrier can be further improved. Simultaneously, the quasifission process in154Sm+160Gd is also investigated with the microscopic dynamics model for the first time. We find that at energies above the Bass barrier, the fusion probability is smaller than 10-5for this reaction, and the nuclear contact time is generally smaller than 1500 fm/c. From the central collisions of Sm+Gd, the neutron-rich fragments such as164,165 Gd,192W can be produced in the Im QMD simulations, which implies that the quasi-fission reaction could be an alternative way to synthesize new neutron-rich heavy nuclei.展开更多
文摘Photofission fragments mass yield for^(232)Th,^(234;238) U,^(237) Np, and^(239;240;242) Pu isotopes are investigated.The calculations are done using a developed approach based on Gorodisskiy's phenomenological formalism. The Gorodisskiy's method is developed to be applied for the neutron-induced fission. Here we revised it for application to photofission. The effect of emitted neutron prior to fission on the fission fragment mass yields has also been studied. The peak-to-valley ratio is extracted for the240 Pu isotope as a function of energy. Obtained results of the present formalism are compared with the available experimental data. Satisfactory agreement is achieved between the results of present approach and the experimental data.
基金The project supported by the National Natural science Foundation of china
文摘The fission angular distributions for the <sup>16</sup>O+<sup>159</sup>Tb,<sup>16</sup>O+<sup>197</sup>Au and <sup>16</sup>O+<sup>209</sup>Bi reac-tions are measured by the solid state nuclear track detectors.After subtraction of the contribu-tion of intermediate mass fragment（IMF）,the fission angular distributions are fitted by thetransitional state statistical model（TSM）and the single-spin standard theory is used to extractthe spins of the fissioning nuclei.The relation between spins and bombarding energy is dis-cussed.
基金Supported by the National Natural Science Foundation of China under Grants Nos 10235020 and 10235030.
文摘The reactions of ^16O＋^204pb, ^82Se＋^138Ba and ^96Zr＋^124Sn lead to the same compound nucleus ^220Th. In terms of the assumption that the surviving probability is independent of entrance channel, we have extracted the fusion hindrance factor from the evaporation residue cross sections for the reactions of ^82Se＋^138 Ba and ^96Zr＋^124Sn and compared with the results calculated using a two-parameter Smoluchowski equation. The theoretical predictions are basically in agreement with the experimental data. It is found that the probability of forming a compact ^220Th is less than 10% for the reactions considered. For the systems more massive than ^220Th, fusion should be much more strongly suppressed due to the competition of quasifission with complete fusion. Understanding of this inhibition is essential to forming new superheavy nuclei.
基金Supported by the Major State Basic Research and Development Programme of China under Contract No G2000077400, the National Natural Science Foundation of China under Grant Nos 10505016, 10235020, 10235030, 10275094, 10075080 and 10575119, the Knowledge Innovation Project of Chinese Academy of Sciences under Grant No KJCX2-SW-N02, National Key Programme for Basic Research of the Ministry of Science and Technology under Grant Nos 2001CCB01200 and 2002CCB00200, and the DFG of Germany.
文摘The lifetimes of a decays of the recently produced isotopes of the elements 112, 114, 116 and the element ^294118 and of some decay products have been calculated theoretically within the Wentzel-Kramers-Brillouin approximation. The a decay barriers have been determined in the quasimolecular shape path within a generalized liquid drop model including the proximity effects between nuclei in a neck, the mass and charge asymmetry and the precise nuclear radius. These calculations provide reasonable estimates for the observed a decay lifetimes. The calculated results have been compared with the results of the density-dependent M3Y effective interaction and the experimental data. It is indicated that the theoretical foundation of the generalized liquid drop model is as good as that of the microscopic DDM3Y model, at least in the sense of predicting the T1/2 values as long as one uses a correct a decay energy. The half lives of these new nuclei are well tested from the consistence of the macroscopic, the microscopic and the experimental data.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10405033, 10405032, 10505026 and 10135030, the Shanghai Development Foundation for Science and Technology under Grant Nos 05XD14021 and 03QA14066, and the Major State Basic Research Programme under Contract No G200077404.
文摘A sequential decay model is used to study isoscaling, i.e. the factorization of the isotope ratios from sources of different isospins and sizes over a broad range of excitation energies, into fugacity terms of proton and neutron number, R21（N, Z） = Y2（ N, Z）/Y1（ N, Z） = Cexp（αN -βZ）. It is found that the isoscaling parameters α and β have a strong dependence on the isospin difference of equilibrated source and excitation energy, no significant influence of the source size on α andβ has been observed. It is found that α and β decrease with the excitation energy and are linear functions of 1/T and △（Z/A）2 or△（N/A）2 of the sources. Symmetry energy coefticient Gsym is constrained from the relationship of a and source △（Z/A）2, /3 and source △（N/A）2.
基金Supported by National Natural Science Foundation of China under Grant Nos.91226102 and 91126010the National Defence Foundation of China under Grant No.B0120110034the National Magnetic Confinement Fusion Science Program of China under Grant No.2013BG106004
文摘Potential energy surfaces of uranium nuclei in the range of mass numbers 229 through 244 are investigated in the framework of the macroscopic-microscopic model and the heights of static fission barriers are obtained in terms of a double-humped structure. The macroscopic part of the nuclear energy is calculated according to Lublin–Strasbourg-drop(LSD) model. Shell and pairing corrections as the microscopic part are calculated with a folded-Yukawa single-particle potential. The calculation is carried out in a five-dimensional parameter space of the generalized Lawrence shapes. In order to extract saddle points on the potential energy surface, a new algorithm which can effectively find an optimal fission path leading from the ground state to the scission point is developed. The comparison of our results with available experimental data and others' theoretical results confirms the reliability of our calculations.
基金Supported by National Natural Science Foundation of China(11675066)Feitian Scholar Project of Gansu Province
文摘The competition between α-decay and spontaneous fission of superheavy nuclei（SHN） is investigated by the generalized liquid drop model（GLDM） and the modified Swiatecki＇s formula respectively. The theoretical decay modes are in good agreement with the experimental results. Predictions are made for as-yet unobserved superheavy nuclei. The theoretical calculations show that the nuclei^298 120,^295 119,^290 118,^291 117,^287 117,^294 116,^289 116,^286 116,^285 116,^284 115,^283 115,^283 114,^282 114,^280 113,^276 112,^275 112,^274 112,^273 111,^272 110,^265 109 may be synthesized experimentally in the near future since they not only have relatively large predicted cross sections but can also be identified via α-decay chains.
基金supported by the National Natural Science Foundation of China(Grant Nos.11422548,11275052,11365005 and 11375062)the Open Project Program of State Key Laboratory of Theoretical Physics,Institute of Theoretical Physics,Chinese Academy of Sciences,China(Grant No.Y4KF041CJ1)
文摘Some nearly-symmetric fusion reactions are systematically investigated with the improved quantum molecular dynamics(Im QMD)model. By introducing two-body inelastic scattering in the Fermi constraint procedure, the stability of an individual nucleus and the description of fusion cross sections at energies near the Coulomb barrier can be further improved. Simultaneously, the quasifission process in154Sm+160Gd is also investigated with the microscopic dynamics model for the first time. We find that at energies above the Bass barrier, the fusion probability is smaller than 10-5for this reaction, and the nuclear contact time is generally smaller than 1500 fm/c. From the central collisions of Sm+Gd, the neutron-rich fragments such as164,165 Gd,192W can be produced in the Im QMD simulations, which implies that the quasi-fission reaction could be an alternative way to synthesize new neutron-rich heavy nuclei.
