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Effect of pre-equilibrium emission on probing postsaddle nuclear dissipation with neutrons

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Chinese Physics C 2016年第9期40卷 52-57页

作者：田舰叶巍 Department of Physics Southeast University

Using the stochastic Langevin model coupled with a statistical decay model, we study the influence of pre-equilibrium（PE） emission on probing postsaddle friction（β） with neutrons. A postsaddle friction value of（14-16.5） ×10^21s^-1 and（11-13） ×10^21s^-1 is obtained from comparing calculated and measured prescission neutron multiplicities of heavy fissioning systems ^248 Fm and ^256Fm in the absence and presence of the deformation ***, it is found that a larger β is required to fit multiplicity data after the PE effect is accounted for, and that the effect becomes stronger when more energy is removed by PE particles. Our findings suggest that, to more accurately determine the postsaddle friction strength through the measurement of prescission neutrons, in addition to incorporating the contribution of PE evaporation source into the experimental multi-source analysis for particle energy spectra in coincidence with fission fragments, on the theoretical side, it is very important to make a precise evaluation of the energy that PE emission carries away from excited compound systems produced in heavy-ion fusion reactions.

关键词： nuclear dissipation Langevin model pre-equilibrium emission neutron

System size effects on probing nuclear dissipation with neutrons

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Chinese Physics C 2010年第5期34卷 551-554页

作者：吴锋叶巍 Department of Fundamental Courses Suqian College of Jiangsu Department of Physics Southeast University

Using a dynamical Langevin equation coupled with a statistical decay model, we calculate the excess of the pre-scission neutron multiplicities over its standard statistical-model values as a function of the nuclear dissipation strength for the three nuclei 19~Os, 2~~Hg, and 21~po which have the same neutron-to-proton ratio N/Z. We find that by decreasing the size of the fissioning nuclei, the effects of nuclear dissipation on the excess of the pre-scission neutron multiplicity are substantially amplified, and that the sensitivity of this excess to the nuclear friction strength is considerably increased as well. We suggest that for those fissioning systems with the same N/Z that are populated in fusion reactions, to obtain a more accurate information of the nuclear dissipation strength by measuring the pre-scission neutron multiplicity, it is best to choose a system with a small size.

关键词： system size effects neutron multiplicity nuclear dissipation

Influence of Deformation on Light Particles as a Probe of nuclear dissipation for a Neutron-Deficient ^178Pb System

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Communications in Theoretical Physics 2006年第4期45卷 687-690页

作者： YE Wei Department of Physics Southeast University Nanjing 210096 China

Using a diffusion model we investigate deformation effects on the sensitivity of different light particles to nuclear dissipation for a rather neutron-deficlent ^178Pb system. Galculations show that deformation significantly increases the sensitivity of neutron emission to dissipation strength, and that this effect becomes stronger with increasing deformation.

关键词： deformation effect isospin effect pre-scission particle multiplicity nuclear dissipation probe diffusion model

Surveying post-saddle nuclear dissipation with protons and α particles as probes

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Chinese Physics C 2010年第1期34卷 45-48页

作者：叶巍 Department of Physics Southeast University

Using a Langevin model, we calculate post-saddle proton and α-particle multiplicities as a function of the post-saddle dissipation strength （β） for the heavy systems 234Cf, 240Cf, 246Cf and 240U. We find that, with increasing isospin of the system, the sensitivity of post-saddle light charged-particle multiplicities to β decreases considerably and, moreover, for 240U the charged-particle multiplicities are no longer sensitive to β. These results suggest that in order to determine the post-saddle friction strength more accurately by measuring the multiplicities of pre-scission protons and α particles, it is best to populate those heavy compound systems with low isospin.

关键词： nuclear dissipation light charged-particle multiplicity isospin effect

Surveying the role of excitation energy in probing nuclear dissipation

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Chinese Physics C 2009年第7期33卷 528-531页

作者：叶巍 Department of Physics Southeast University

A dynamical Langevin model is employed to calculate the excess of the evaporation residue cross sections of the ^194Pb nucleus over that predicted by the standard statistical model as a function of nuclear dissipation strength. It is shown that large excitation energy can increase the effects of nuclear dissipation on the excess of the evaporation residues and the sensitivity of this excess to the dissipation strength,and that more higher excitation energies have little contribution to further raising this sensitivity. These results suggest that on the experimental side,producing those compound systems with moderate excitation energy is sucient for a good determination of the pre-saddle nuclear dissipation strength by measuring the evaporation residue cross section,and that forming an extremely highly excited system does not considerably improve the sensitivity of evaporation residues to the dissipation strength.

关键词： nuclear dissipation excitation energy evaporation residue cross section Langevin equation

A Detailed Study of Pre-scission γ Emission as a Probe of nuclear dissipation

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Communications in Theoretical Physics 2007年第4X期48卷 710-712页

作者： WU Feng YE Wei CHEN Na Department of Physics Southeast University Nanjing 210096 China Department of Mathematics Nanjing University of Finance & Economics Nanjing 210003 China

Using a Langevin equation coupled with a statistical model, we calculate pre-scission giant dipole resonance （GDR） γ-ray multiplicity of nuclei 194 pb, 200Pb, 206Pb, and 200 Os. It is demonstrated that with increasing the isospin asymmetry of these fissioning nuclei the sensitivity of the emitted γ multiplicity to the nuclear viscosity coefficient is decreased significantly. For 200Os nuc/eus, this γ-ray emission is no longer sensitive to the magnitude of the viscosity coefficient. In addition, the effect of the isospin asymmetry on the γ rays as a probe of nuclear dissipation is reduced with increasing angular momentum. These results suggest that to obtain a more accurate information of the viscosity coemfficient by the measurement of pre-scission GDR γ-ray multiplicity it is better to choose those compound systems with small isospin asymmetry and low spin.

关键词： giant dipole resonance γ-ray multiplicity nuclear dissipation isospin asymmetry effect Langevin equation

Roles of Isospin in Evaporation Residue Cross Section as a Probe of nuclear dissipation

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Communications in Theoretical Physics 2008年第3期49卷 739-742页

作者： CHEN Na YE Wei Department of Applied Mathematics Nnnjing University of Finance ＆ Economics Nnnjing 210046 China Department of Physics Southeast University Nanjing 210096 China

The influence of isospin on the excess of evaporation residue cross section over its standard statistical-model value for nuclei ^194pb, ^200Pb, and ^206pb is studied via a Langevin equation coupled with a statistical decay model. The magnitude of this excess for a low-isospin fissioning nucleus is shown to be larger and its dependence on the nuclear viscosity coefficient to be stronger than those of a high-isospin fissioning nucleus. These results suggest that to obtain a more accurate information of viscosity coefficient inside the saddle point by measuring evaporation residue cross sections, we had better choose those compound systems with small isospin.

关键词： evaporation residue cross section isospin effect nuclear dissipation Langevin equation

Effects of N/Z on Spin Distribution of Evaporation Residue Cross Section as a Probe of nuclear dissipation

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Communications in Theoretical Physics 2008年第9期50卷 729-732页

作者： YE Wei YANG Hong-Wei CHEN Na Department of Physics Southeast University Nanjing 210096 China Depaxtment of Applied Mathematics Nanjing University of Finance ＆ Economics Nanjing 210046 China

The spin distribution of the evaporation residue cross section of nuclei ^194pb, ^200Pb, ^206Pb, and ^200 Os are calculated via a Langevin equation coupled with a statistical decay model. It is shown that with increasing the neutronto-proton ratio （N/Z） of the system, the sensitivity of the significantly. Moreover, for ^200Os this spin distribution is no spin distribution to the nuclear dissipation is decreased longer sensitive to the nuclear dissipation. These results suggest that to obtain a more accurate pre-saddle viscosity coefficient through the measurement of the evaporation residue spin distribution, it is best to yield those compound systems with low N/Z.

关键词： evaporation residue spin distribution N/Z effect nuclear dissipation Langevin equation

Investigating the fission dynamics of the following neutron shell closed nuclei within a stochastic dynamical approach:^(210)Po,^(212)Rn,and ^(213)Fr

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Chinese Physics C 2023年第3期47卷 127-137页

作者： Divya Arora P.Sugathan A.Chatterjee Inter-University Accelerator Centre Aruna AsafAli MargNew Delhi 110067India

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 *** 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 ***,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 *** 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 *** relevant calculations are performed by using a phenomenological universal friction form factor with no ad-hoc adjustment of the model ***,we note a significant deviation,beyond experimental errors,for some Frisotopes.

关键词： fusion-fission nuclear dissipation dynamical model neutron shell closure saddle shell corrections