与核密度及温度相关的核子相对论微观光学势

在Walecka模型、热场动力学和相对论Dirac-Bruckner-Hartree-Fock计算结果基础上,研究了在不同核密度和各种温度情况下的核子相对论微观光学势及其相应的薛定谔等效势和平均自由程,计算结果表明,对于不同的温度,核子的薛定谔等效势与平均自由程随核密度变化较为敏感,而核温度对核子的薛定谔等效势和平均自由程的影响随着核密度的增加变大.     

Investigation of Self-Consistent Relativistic Microscopic Optical Potential

In Dirac-Brueckner calculations for nuclear matter,the average binding energy per nucleon versus density curve is not uniquely defined if coupling to anti-particle is neglected.According to the Hugenholtz-Van Hove theorem,a constraint requires that the nucleon separation energy equals to the fermi energy at saturation density.Choosing saturation energy as empirical value E_B/A=－15.8MeV,the self-consistent calculation leads to the saturation density k_f=1.41fm^－1 and effective mass m*=0.52m,in compressive coefficient k=208MeV.Applying the first law of thermodynamics,self-consistent effective mass (real scalar potential) and the binding energy per nucleon as function of the nuclear density can be obtained.With the realistic nucleon-nucleon interaction (Bonn potential),the vector potential can be obtained from solving the RBBG equation,which weakly depends on the momentum.The cross section and spin observables of the nucleon-nucleus scattering are studied with this new self-consistent relativistic microscopic optical potential.     

相对论微观光学势中的同位旋相关项

采用Dirac Brueckner-Hartree-Fock方法研究同位旋相关的相对论微观光学势, 讨论了其同位旋相关项的处理.采用定域密度近似得到有限核的微观光学势, 以²⁰⁸Pb为例讨论了光学势的同位旋相关性,并与唯象的Lane势进行了比较.     

An Investigation of Relativistic Microscopic Optical Potential in Terms of Relativistic Brueckner-Bethe-Goldstone Equation

Relativistic microscopic optical potential of nucleon-nucleus is derived from the relativistic Brueckner-Bethe-Goldstone (RBBG) equation.The complex effective mass of a nucleon is determined by a fit to 200MeV p-⁴⁰Ca scattering data.The relativistic microscopic optical potentials with this effective mass are obtained from RBBG for p-¹⁶O,⁴⁰Ca,⁹⁰Zr and ²⁰⁸Pb scattering in energy range from 160 to 180MeV.The microscopic optical potential is used to study the proton-⁴⁰Ca scattering problem at 200MeV.The results,such as defferential cross section,analyzing power and spin rotation function are compared with those calculated from phenomenological relativistic optical potential.     

Neutron Relativistic Phenomenological and Microscopic Optical Potentials

The experimental data of the neutron total cross section σ_t,nonelastic cross section σ_non and elastic scattering angular distribution σ_el(θ) for ten target nuclei ranging from ¹²C to ²³⁸U with incident energies E_n=20—1000MeV were used to optimize the relativistic phenomenological optical potential (RPOP) through automatic search of the best parameters by computer.In addition,a relativistic microscopic optical potential (RMOP) based on Walecka model were also used to analyze the same data and compare with the RPOP.
Through comparison between these two kinds of relativistic optical potential hints in improving both the RMOP and RPOP is indicated.     

The Contribution of the Fourth Order Exchange Diagrams to The Relativistic Microscopic Optical Potential

The contribution of the fourth order exchange diagrams is first studied to the imaginary part of nucleon self-energy,the relativistic microscopic optical potential and the Schrodinger equivalent potential of the relativistic microscopic optical potential based on Walecka's meson-nucleon model.     

N－N关联和有限核相对论平均场方法

密度有关的核子－介子相互作用耦合常数是在相对论平均场近似下用核物质的相对论Ｂｒｕｅｃｋｎｅｒ－Ｈａｒｔｒｅｅ－Ｆｏｃｋ近似计算的自能参数化得到的．这种密度有关的相互作用考虑了介质中Ｎ－Ｎ关联效应，用这种密度有关的相互作用来研究有限核的基态性质，如单粒子能级，平均结合能，电荷均方根半径，与实验值较好地符合，同时还与其它模型的结果进行了比较。     

Second Order Correction of Relativistic Optical Potential

The imaginary part of the off-energy shell optical potential of a nucleon in nuclear matter, where the polarization and correlation contribution of the exchanges of the σ and ω mesons are taken into account, is derived in the framework of the relativistic meson-nucleon field theory. The second order correction of the real part of the optical potential is calculated in terms of the dispersion relation and the effective mass of a nucleon in the nuclear medium is also investigated in this paper.     

A Microscopic Optical Potential for Deuteron

The microscopic optical potential for deuteron is obtained by folding the microscopic optical potentials of its constituent nucleons. The optical potential is used to predict the reaction cross sections and the elastic scattering angular distributions for some spherical target nuclei, and the results of theoretical calculation are compared with the experimental data available.     

The Effect of Interaction Range in Relativistic Microscopic Optical Potentials

Starting from the Walecka model about relativistic nucleon-meson field theory,the effect of interaction range in the relativistic microscopic optical potentials for nucleon-nucleus is included by folding the optical potentials in Local Density Approximity with nucleon-nucleon interaction potentials from the Walecka model.The present potentials are used to analyze the proton elastic scattering from nuclei.The agreement of the present calculation with experiment data is better than that of LDA.     

Full and Partial Thermalization of Nucleons in Relativistic Nucleus-Nucleus Collisions

We propose a mechanism of thermalization of nucleons in relativistic nucleus-nucleus collisions. Our model belongs, to a certain degree, to the transport ones; we consider the evolution of the system, but we parametrize this development by the number of collisions of every particle in the system rather than by the time variable. We based on the assumption that the nucleon momentum transfer after several nucleon-nucleon (-hadron) collisions becomes a random quantity driven by a proper distribution.     

Analyses of Relativistic Optical Potential for Medium Energy Proton

The influence of the parameters of the relativistic optical potential on the nucleon scattering properties,such as cross sections,angular distributions and spin observables etc.,is studied based on a set of global Dirac phenomenological optical potentials.It is shown that,in contrast with the case at low energies.the total scattering cross sections vary slowly as the energy and weakly depend on the potentials at E_p<200MeV.The differential cross sections and spin observables depend not only on the volume integrals of the optical potentials,but also on their strengths and shapes.The applicability of the relativistic microscopic optical potentia based on Walecka model in the medium energy region is also discussed in this paper.     

Electromagnetic Form Factors of Nucleons in a Relativistic Three-Quark Model

We study electromagnetic form factors of nucleons within a relativistic three-quark model with a Gaussian shape for the nucleon-quark vertex. The allowed regions for two adjustable parameters, the range parameter Λ _N in the Gaussian and the constituent quark mass m _q , are obtained from fitting the data for magnetic moments and electromagnetic radii of nucleons. It is found that these observables, when calculated with m _q = 420 MeV and Λ _N = 1.25 GeV, agree very well with the experimental data. For these parameter values, however, our model underestimates the electromagnetic form factors of the nucleon at high momentum transfers for the calculated range O ≤ Q²≤ 1 GeV². Received April 10, 1996; revised June 20, 1996; accepted for publication July 19, 1996     

Charged Multiplicity Density and Number of Participant Nucleons in Relativistic Nuclear Collisions

The energy and centrality dependencies of charged particle pseudorapidity density in relativistic nuclearcollisions were studied using a hadron and string cascade model, JPCIAE. Both the relativistic p+p experimental dataand the PHOBOS and PHENIX Au+Au data at RHIC energy could be fairly reproduced within the framework ofJPCIAE model and without retuning the model parameters. The predictions for Pb + Pb collisions at the LHC energywere also given. We computed the participant nucleon distributions using different methods. It was found that thenumber of participant nucleons is not a well defined variable both experimentally and theoretically. Thus it may beinappropriate to use the charged particle pseudorapidity density per participant pair .as a function of the number ofparticipant nucleons for distinguishing various theoretical models.     

Measurements of the Mean Free Paths of the Proton and Pions in the Nuclear Matter

The results of measuring the yields of neutral and charged pions in the (, p) reaction on Li, C, and Al nuclei are presented as functions of the proton energy and azimuth angle of pion emission. The experiment was performed in the second resonance region of the photon energy. The measurements are analyzed within the model of single and double quasi-free pion photoproduction. The energy dependences of the mean free path of the proton and neutral and charged pions are obtained based on the dependence of the reaction yield on the atomic number of the target nucleus.     

有限温度下磁极化子中的平均光学声子数

采用线性组合算符方法，导出了有限温度下磁极化子中的平均光学声子数，讨论了平均声子数与温度T、磁场B和坐标z之间的关系。     

Relativistic Morse Potential and Tensor Interaction

In this paper, by applying the Pekeris approximation, we present solutions of the Dirac equation for the Morse potential including a Coulomb-like tensor potential with arbitrary spin-orbit coupling number κ under spin and pseudospin symmetry limits. The generalized parametric Nikiforov–Uvarov method is used to obtain energy eigenvalues and corresponding eigenfunctions in their closed forms. We show that tensor interaction removes degeneracies between spin and pseudospin doublets. Some numerical results are given, too.