为适应聚变-裂变混合堆设计及其相关研究的需求制作混合多用途核数据库HENDL(HybridEvaluated Nuclear Data Library)的升级版本HENDL2.0。评价核数据来源主要选用美国公布的ENDF/B-Ⅶ.0库和国际原子能机构(IAEA/NDS)发布的聚变库FENDL-...为适应聚变-裂变混合堆设计及其相关研究的需求制作混合多用途核数据库HENDL(HybridEvaluated Nuclear Data Library)的升级版本HENDL2.0。评价核数据来源主要选用美国公布的ENDF/B-Ⅶ.0库和国际原子能机构(IAEA/NDS)发布的聚变库FENDL-2.1。利用蒙特卡罗粒子输运程序MCNP以及FDS团队自主研发的大型集成多功能中子学计算与分析系统VisualBUS程序进行模拟计算,对已有的一些数据较为完备的基准实验例题进行基准测试和比较分析以检验混合库HENDL2.0的有效性和可信性。展开更多
The angular distributions of fission fragments for the 32S+184W reaction near Coulomb barrier energies are measured. The ex perimental fission excitation function is obtained. The measured fission cross sections are d...The angular distributions of fission fragments for the 32S+184W reaction near Coulomb barrier energies are measured. The ex perimental fission excitation function is obtained. The measured fission cross sections are decomposed into fusion-fission, quasi-fission and fast fission contributions by the dinuclear system (DNS) model. The hindrance to completing fusion both at small and large collision energies is explained. The fusion excitation functions of 32S+90,96Zr in an energy range from above to below the Coulomb barrier are measured and analyzed within a semi-classical model. The obvious effect of positive Q-value multi-neutron transfers on the sub-barrier fusion enhancement is observed in the 32S+96Zr system. In addition, the excitation functions of quasi-elastic scattering at a backward angle have been measured with high precision for the systems of 16O+208Pb, 196Pt, 184W, and 154,152Sm at energies well below the Coulomb barrier. Considering the deformed coupling effects, the extracted diffuseness parameters are close to the values extracted from the systematic analysis of elastic and inelastic scattering data. The elastic scattering angular distribution of 17F+12C at 60 MeV is measured and calculated by using the continuum-discretized coupled-channels (CDCC) approach. It is found that the diffuseness parameter of the real part of core-target potential has to be increased by 20% to reproduce the experimental result, which corresponds to an increment of potential depth at the surface re gion. The breakup cross section and the coupling between breakup and elastic scattering are small.展开更多
To validate neutronics calculation for the blanket design of fusion-fission hybrid reactor,experiments for measuring reaction rates inside two simulating assemblies are performed.Two benchmark assemblies were develope...To validate neutronics calculation for the blanket design of fusion-fission hybrid reactor,experiments for measuring reaction rates inside two simulating assemblies are performed.Two benchmark assemblies were developed for the neutronics experiments.A D-T fusion neutron source is placed at the center of the setup.One of them consists of three layers of depleted uranium shells and two layers of polyethylene shells,and these shells are arranged alternatively.The ^(238)U capture reaction rates are measured using depleted uranium foils and an HPGe gamma spectrometer.The fission reaction rates are measured using a fission chamber coated with depleted uranium.The other assembly consists of depleted uranium and LiH shells.The tritium production rates are measured using the lithium glass scintillation detector which is placed in the LiH region of the assembly.The measured reaction rates are compared with the calculated ones predicted using MCNP code,and C/E values are obtained.展开更多
Patterns of variation in the size of vulture foraging groups,and their ecological causes and consequences,remain litle explored despite strong links with the carrion recycling service that this key functional group pr...Patterns of variation in the size of vulture foraging groups,and their ecological causes and consequences,remain litle explored despite strong links with the carrion recycling service that this key functional group provides.We documented the group size-frequency pattern of Andean con-dors Vultur gryphus gathered to feed on 42 equine carcasses experimentally placed in Bolivia,between 2012 and 2019,along an elevation range of 1,300-4,500 m asl.Based on the location(altitude and latitude)of the foraging groups,we examined the relationship between their size and species'population parameters(size and trend),habitat conditions,and livestock carcass availability and predictability.Condors utilized a high frequency(93%)of carcasses forming groups that ranged from 1 to 80 individuals(mean=25,median=18)and shaped a"lazy-J curve"typical pattern of size-frequency distribution whereby few groups(5,12%)were large(>55 individuals)and most(21,50%)were relatively small(<19 individuals).Group size related to altitude in that most larger groups formed at lower sites(below c.3,000 m asl),likely following an altitudinal gradient whereby larger groups are more likely to form around larger carcasses(i.e.,cattle),which are more likely to occur at lower elevations.Regardless of population size,group size could be an adaptive response of condors via local enhancement for improving individual scavenging efficiency.Many information gaps on this topic still exist,thus we provide a set of questions to address them,especially amidst the unrestricted impacts of human activities that condition vulture survival globally.展开更多
We discuss a hardship in synthesis of heaviest super heavy elements in massive nuclei reactions due to the hindrance to complete fusion of reacting nuclei caused on the onset of quasifission process which strongly com...We discuss a hardship in synthesis of heaviest super heavy elements in massive nuclei reactions due to the hindrance to complete fusion of reacting nuclei caused on the onset of quasifission process which strongly competes with complete fusion and due to the strong increase of fission yields along the de-excitation cascade of the compound nucleus in comparison with the evaporation residue formation.The hindrance to formation of compound nucleus and evaporation residue is determined by the characteristic of the entrance channel.展开更多
A fusion-fission hybrid conceptual reactor is established. It consists of a DT neutron source and a spherical shell of depleted uranium and hydrogen lithium. The tritium production rate （TPR） distribution in the con...A fusion-fission hybrid conceptual reactor is established. It consists of a DT neutron source and a spherical shell of depleted uranium and hydrogen lithium. The tritium production rate （TPR） distribution in the conceptual reactor was measured by DT neutrons using two sets of lithium glass detectors with different thicknesses in the hole in the vertical direction with respect to the D＋ beam of the Cockcroft-Walton neutron generator in direct current mode. The measured TPR distribution is compared with the calculated results obtained by the three- dimensional Monte Carlo code MCNP5 and the ENDF/B-VI data file. The discrepancy between the measured and calculated values can be attributed to the neutron data library of the hydrogen lithium lack S（α, β） thermal scattering model, so we show that a special database of low-energy and thermal neutrons should be established in the physics design of fusion-fission hybrid reactors.展开更多
The fragment angular distributions of fusion-fission reactions for the systemsof <sup>16</sup>O+<sup>232</sup>Th,<sup>19</sup>F+<sup>232</sup>Th and <sup>16</su...The fragment angular distributions of fusion-fission reactions for the systemsof <sup>16</sup>O+<sup>232</sup>Th,<sup>19</sup>F+<sup>232</sup>Th and <sup>16</sup>O+<sup>238</sup>U at near-and sub-barrier energies were measured.The measured fragment anisotropies obviously deviate from the predictions ofscission-point transition-state model.We also compared the excitation energy of tiltingmode with the statistical assumption.It was found that thermal equilibrium is not estab-lished at scission for the reactions studied.展开更多
The dissipative dynamics of nuclear fission is a well confirmed phenomenon that can be either described by a Kramers-modified statistical model or by a dynamical model employing the Langevin equation.Although dynamica...The dissipative dynamics of nuclear fission is a well confirmed phenomenon that can be either described by a Kramers-modified statistical model or by a dynamical model employing the Langevin equation.Although dynamical models as well as statistical models incorporating fission delays have been found to explain the measured fission observables in several studies,they present conflicting results for shell closed nuclei in the mass region of 200.Notably,an analysis of the recent data on neutron shell closed nuclei in the excitation energy range of 40-80 MeV failed to provide a satisfactory description of the data,which was attributed to a mismatch with shell effects and/or entrance channel effects,without reaching a definite conclusion.In the present study,we demonstrate that a well established stochastic dynamical code can simultaneously reproduce the available data for pre-scission neutron multiplicities and fission and evaporation residue excitation functions for the following neutron shell closed nuclei^(210)Po and^(212)Rn and their isotopes^(206)Po and^(214,216)Rn without the need for including any extra shell or entrance channel effects.The relevant calculations are performed by using a phenomenological universal friction form factor with no ad-hoc adjustment of the model parameters.However,we note a significant deviation,beyond experimental errors,for some Frisotopes.展开更多
A model for cold-fusion reactions related to the synthesis of super-heavy nuclei in collisions of heavy projectile-nuclei with a ^(208)Pb target nucleus is discussed.In the framework of this model,the production of th...A model for cold-fusion reactions related to the synthesis of super-heavy nuclei in collisions of heavy projectile-nuclei with a ^(208)Pb target nucleus is discussed.In the framework of this model,the production of the com-pound nucleus by two paths,the di-nuclear system path and the fusion path,are taken into account simultaneously.The formation of the compound nucleus in the framework of the di-nuclear system is related to the transfer of nucle-ons from the light nucleus to the heavy one.The fusion path is linked to the sequential evolution of the nuclear shape from the system of contacting nuclei to the compound nucleus.It is shown that the compound nucleus is mainly formed by the fusion path in cold-fusion reactions.The landscape of the potential energy related to the fusion path is discussed in detail.This landscape for very heavy nucleus-nucleus systems has an intermediate state,which is linked to the formation of both the compound nucleus and the quasi-fission fragments.The decay of the intermediate state is taken into account in the calculation of the compound nucleus production cross sections and the quasi-fission cross sections.The values of the cold-fusion cross sections obtained in the model agree well with the experimental data.展开更多
文摘为适应聚变-裂变混合堆设计及其相关研究的需求制作混合多用途核数据库HENDL(HybridEvaluated Nuclear Data Library)的升级版本HENDL2.0。评价核数据来源主要选用美国公布的ENDF/B-Ⅶ.0库和国际原子能机构(IAEA/NDS)发布的聚变库FENDL-2.1。利用蒙特卡罗粒子输运程序MCNP以及FDS团队自主研发的大型集成多功能中子学计算与分析系统VisualBUS程序进行模拟计算,对已有的一些数据较为完备的基准实验例题进行基准测试和比较分析以检验混合库HENDL2.0的有效性和可信性。
基金supported by the National Natural Science Foundation of China (Grant Nos. 10575134, 10675169 and 10735100)the Major State Basic Research Developing Program (Grant No. 2007CB815003)
文摘The angular distributions of fission fragments for the 32S+184W reaction near Coulomb barrier energies are measured. The ex perimental fission excitation function is obtained. The measured fission cross sections are decomposed into fusion-fission, quasi-fission and fast fission contributions by the dinuclear system (DNS) model. The hindrance to completing fusion both at small and large collision energies is explained. The fusion excitation functions of 32S+90,96Zr in an energy range from above to below the Coulomb barrier are measured and analyzed within a semi-classical model. The obvious effect of positive Q-value multi-neutron transfers on the sub-barrier fusion enhancement is observed in the 32S+96Zr system. In addition, the excitation functions of quasi-elastic scattering at a backward angle have been measured with high precision for the systems of 16O+208Pb, 196Pt, 184W, and 154,152Sm at energies well below the Coulomb barrier. Considering the deformed coupling effects, the extracted diffuseness parameters are close to the values extracted from the systematic analysis of elastic and inelastic scattering data. The elastic scattering angular distribution of 17F+12C at 60 MeV is measured and calculated by using the continuum-discretized coupled-channels (CDCC) approach. It is found that the diffuseness parameter of the real part of core-target potential has to be increased by 20% to reproduce the experimental result, which corresponds to an increment of potential depth at the surface re gion. The breakup cross section and the coupling between breakup and elastic scattering are small.
基金supported by the National Special Magnetic Confinement Fusion Energy Research (No.2010GB111002),China
文摘To validate neutronics calculation for the blanket design of fusion-fission hybrid reactor,experiments for measuring reaction rates inside two simulating assemblies are performed.Two benchmark assemblies were developed for the neutronics experiments.A D-T fusion neutron source is placed at the center of the setup.One of them consists of three layers of depleted uranium shells and two layers of polyethylene shells,and these shells are arranged alternatively.The ^(238)U capture reaction rates are measured using depleted uranium foils and an HPGe gamma spectrometer.The fission reaction rates are measured using a fission chamber coated with depleted uranium.The other assembly consists of depleted uranium and LiH shells.The tritium production rates are measured using the lithium glass scintillation detector which is placed in the LiH region of the assembly.The measured reaction rates are compared with the calculated ones predicted using MCNP code,and C/E values are obtained.
基金funded by The Peregrine Fund's Neotropical Science and Student Education Program,a British Ornithologists'Union Small Ornithological Research Grant,a Neotropical Birding and Conservation(formerly known as Neotropical Bird Club)Conservation Award granted to D.Méndez in 2014,and two 2018 grants to D.Méndez,one from the Rufford Small Grants Foundation(24763-1)another from the International Foundation for Science(I-1-D-6156-1).
文摘Patterns of variation in the size of vulture foraging groups,and their ecological causes and consequences,remain litle explored despite strong links with the carrion recycling service that this key functional group provides.We documented the group size-frequency pattern of Andean con-dors Vultur gryphus gathered to feed on 42 equine carcasses experimentally placed in Bolivia,between 2012 and 2019,along an elevation range of 1,300-4,500 m asl.Based on the location(altitude and latitude)of the foraging groups,we examined the relationship between their size and species'population parameters(size and trend),habitat conditions,and livestock carcass availability and predictability.Condors utilized a high frequency(93%)of carcasses forming groups that ranged from 1 to 80 individuals(mean=25,median=18)and shaped a"lazy-J curve"typical pattern of size-frequency distribution whereby few groups(5,12%)were large(>55 individuals)and most(21,50%)were relatively small(<19 individuals).Group size related to altitude in that most larger groups formed at lower sites(below c.3,000 m asl),likely following an altitudinal gradient whereby larger groups are more likely to form around larger carcasses(i.e.,cattle),which are more likely to occur at lower elevations.Regardless of population size,group size could be an adaptive response of condors via local enhancement for improving individual scavenging efficiency.Many information gaps on this topic still exist,thus we provide a set of questions to address them,especially amidst the unrestricted impacts of human activities that condition vulture survival globally.
文摘We discuss a hardship in synthesis of heaviest super heavy elements in massive nuclei reactions due to the hindrance to complete fusion of reacting nuclei caused on the onset of quasifission process which strongly competes with complete fusion and due to the strong increase of fission yields along the de-excitation cascade of the compound nucleus in comparison with the evaporation residue formation.The hindrance to formation of compound nucleus and evaporation residue is determined by the characteristic of the entrance channel.
基金Supported by Chinese Special Project for ITER (2010GB111002)
文摘A fusion-fission hybrid conceptual reactor is established. It consists of a DT neutron source and a spherical shell of depleted uranium and hydrogen lithium. The tritium production rate （TPR） distribution in the conceptual reactor was measured by DT neutrons using two sets of lithium glass detectors with different thicknesses in the hole in the vertical direction with respect to the D＋ beam of the Cockcroft-Walton neutron generator in direct current mode. The measured TPR distribution is compared with the calculated results obtained by the three- dimensional Monte Carlo code MCNP5 and the ENDF/B-VI data file. The discrepancy between the measured and calculated values can be attributed to the neutron data library of the hydrogen lithium lack S（α, β） thermal scattering model, so we show that a special database of low-energy and thermal neutrons should be established in the physics design of fusion-fission hybrid reactors.
基金The project supported by the National Natural Science Foundation of China under the contract No.19275067.
文摘The fragment angular distributions of fusion-fission reactions for the systemsof <sup>16</sup>O+<sup>232</sup>Th,<sup>19</sup>F+<sup>232</sup>Th and <sup>16</sup>O+<sup>238</sup>U at near-and sub-barrier energies were measured.The measured fragment anisotropies obviously deviate from the predictions ofscission-point transition-state model.We also compared the excitation energy of tiltingmode with the statistical assumption.It was found that thermal equilibrium is not estab-lished at scission for the reactions studied.
基金D.A.acknowledges the financial support from the University Grants Commission(UGC),Government of India,received in the form of a research fellowship(Ref.No.19/06/2016/(i)EU-V,Sr.No.2061651303)。
文摘The dissipative dynamics of nuclear fission is a well confirmed phenomenon that can be either described by a Kramers-modified statistical model or by a dynamical model employing the Langevin equation.Although dynamical models as well as statistical models incorporating fission delays have been found to explain the measured fission observables in several studies,they present conflicting results for shell closed nuclei in the mass region of 200.Notably,an analysis of the recent data on neutron shell closed nuclei in the excitation energy range of 40-80 MeV failed to provide a satisfactory description of the data,which was attributed to a mismatch with shell effects and/or entrance channel effects,without reaching a definite conclusion.In the present study,we demonstrate that a well established stochastic dynamical code can simultaneously reproduce the available data for pre-scission neutron multiplicities and fission and evaporation residue excitation functions for the following neutron shell closed nuclei^(210)Po and^(212)Rn and their isotopes^(206)Po and^(214,216)Rn without the need for including any extra shell or entrance channel effects.The relevant calculations are performed by using a phenomenological universal friction form factor with no ad-hoc adjustment of the model parameters.However,we note a significant deviation,beyond experimental errors,for some Frisotopes.
文摘A model for cold-fusion reactions related to the synthesis of super-heavy nuclei in collisions of heavy projectile-nuclei with a ^(208)Pb target nucleus is discussed.In the framework of this model,the production of the com-pound nucleus by two paths,the di-nuclear system path and the fusion path,are taken into account simultaneously.The formation of the compound nucleus in the framework of the di-nuclear system is related to the transfer of nucle-ons from the light nucleus to the heavy one.The fusion path is linked to the sequential evolution of the nuclear shape from the system of contacting nuclei to the compound nucleus.It is shown that the compound nucleus is mainly formed by the fusion path in cold-fusion reactions.The landscape of the potential energy related to the fusion path is discussed in detail.This landscape for very heavy nucleus-nucleus systems has an intermediate state,which is linked to the formation of both the compound nucleus and the quasi-fission fragments.The decay of the intermediate state is taken into account in the calculation of the compound nucleus production cross sections and the quasi-fission cross sections.The values of the cold-fusion cross sections obtained in the model agree well with the experimental data.
