Nuclear Matter Density,Collision Number and Entropy in Dynamics Process of Intermediate High Energy Heavy Ion Collision

The nuclear matter density,collision number and entropy in the dynamic process of heavy ion collision ⁴⁰Ca+⁴⁰Ca at E_L=400MeV/A for very central collision were calculated.The results show that the nuclear spatial density distributions depend mainly on the mean field but rarely on the nucleonnucleon collisions.The density distribution in the momentum space,collision number and entropy are influenced by the mean field and nucleon-nucleon collision,especially the medium effects.     

HEAVY ION COLLISION DYNAMICS IN FERMI DOMAIN (Ⅱ) DYNAMICS DEPENDENCE OF IMPACT PARAMETER

The peripheral collision mechanisms have been systemic ally studied via the Boltzmann-Uehling-Uhlenbeck theory in the Fermi domain for ²⁰Ne+²⁰Ne collision system.The characters of energy dependence and the intermediate mass fragment production in the process of incomplete deep inelastic collision were discussed.     

重离子碰撞两体关联输运理论──Ⅰ．理论模型：相干态表象的构造与基本运动方程

应用相干态表象和两体关联动力学，建立了非相对论重离子碰撞两体关联输运理论ＴＢＣＴＴ（Ｔｗｏ—ＢｏｄｙＣｏｒｒｅｌａｔｉｏｎＴｒａｎｓｐｏｒｔＴｈｅｏｒｙ）．这一理论包括了时间相关的平均场．泡利阻塞和两体碰撞效应，它能够描述重离子碰撞过程中非均匀核物质的演化、涨落效应和碎裂的动力学形成．     

Two -Body Correlation Transport Theory for Heavy Ion Collisions Ⅰ. Theory Model: Construction of Coherent State Representation and Basic Equations of Motion

A two-body correlation transport theory(TBCTT) for describing the dynamical process in heavy ion collisions(HIC)is established by means of time-dependent coherent single particle state representations and the two-body correlation dynamics.Containing time-dependent mean field effect, Pauli block, and two-body collisions,this model is capable of describing the time-evolution of nonuniform nuclear matter,fluctuation effects and dynamical formation of fragments in HIC.     

Target Residues from the Interaction of Copper with 40MeV/u 40Ar Ions

Cross Sections and average forward recoil range FW were measured for target residues from the interaction of Cu with 40MeV/u ⁴⁰Ar ions using off-line y-ray spectroscopy.The mass yield distribution was obtained with assumption of charge distribution.The linear momentum transfer was calculated from FW values.A comparison with similar results of ¹²C+Cu and ²⁰Ne+Cu reactions indicates that the fractional linear momentum transfer,corresponding to central collisions,decreases with increasing projectile mass at the same energy per nucleon. However,the excitation energy of the composite system created from the collisions of Cu with ⁴⁰Ar ions reached the value of 5.3MeV /u and was higher than those from the collisions with ¹²C and ²⁰Ne ions.     

Emission of prompt nucleons in heavy ion collisions

We describe a simple dynamical model for the production of prompt nucleons at the very beginning of a heavy ion collision. Approximations often used in previous calculations (neglect of Pauli blocking, of window velocity and of its extension) have been checked. We apply the model to the calculation of prompt emitted neutrons in incomplete fusion reactions observed on the²⁰Ne+¹⁶⁵Ho system at 220, 402 and 700 MeV. Results of the model are extensively discussed.     

Radial Expansion Flow in Reactions of 40Ca+58Fe and 40Ca+58Ni

By means of using an isospin-dependent Boltzmann-Langevin equation which includes isospin-dependent symmetry energy, Coulomb energy, isospin-dependent nucleon-nucleon cross sections, Pauli blocking, and initialization, the radial expansion flow of reaction systems ⁴⁰Ca+⁵⁸Ni and ⁴⁰Ca+⁵⁸Fe at 53, 100, 150, and 200 MeV/u in the central collisions were studied. It has shown that the more neutron rich system exhibits smaller radial expansion flow. It was found that the neutron rich system had smaller threshold energy which may provide a new method to determine the isospin dependent nuclear equation of state from calculated result and linear fitting result.     

Pauli Correlation Effect for the Elastic Scattering of Protons by Different Nuclei at 800 MeV

The angular distributions of the elastic scattering of protons at an energy of 800 MeV by ¹⁶O and ²⁰Ne nuclei are described in terms of the optical model scattering theory. Single folding model is applied to calculate the optical potential taking the effective nucleon-nucleon interaction to be in two forms. One form includes the zero-range pseudo-potential term and the other includes a two-body Pauli correlation function. Analytical expressions for the real part of the optical potential are obtained for both forms. The imaginary part of the optical potential is taken to be of the Woods-Saxon's shape. It is found that introducing the Pauli correlation function improves the agreement with the experimental data for the elastic scattering differential cross-sections of protons with the target nuclei ¹⁶O and ²⁰Ne.     

多体关联动力学中的自洽平均场

本文仔细地讨论了量子多体关联动力学中的广义自洽平均场,证明无论动态还是定态自洽平均场都是存在的。多体关联通过两体关联c₂及其相应的碰撞项I进入平均场。I的作用是双重的:对单粒子运动量子态的动力学效应和对单粒子态填充数的影响。多体关联还在多体系统的能量表达式中表现出来,使得该表达式不同于通常的HF-Brueckner理论中的表达式。 关键词：     

Homogeneous saturation of the 6328 Å neon laser transition due to collisions in the weak collision model

Measurement of the collision broadened lineshapes of the 6328 Å Ne laser transition in absorbing ²⁰Ne and amplifying 7 : 1 ³He : ²⁰Ne discharges indicate that the transition saturates with a Doppler component as well as the Lorentzian holes expected of a Doppler broadened line. The homogeneous saturation, caused by elastic velocity-changing collisions, is much stronger in ²⁰Ne than in 7 : 1 ³He : ²⁰Ne. The results are in good agreement with a rate equation formulation in which the effect of velocity-changing collisions giving rise to cross-relaxation is introduced through the Fokker-Planck probability function.     

Classical many-body model for heavy-ion collisions incorporating the Pauli principle

A classical model for heavy-ion collisions, introduced previously, has been extended to include certain effects of the Pauli principle. All nucleons are treated equally. They obey classical dynamics and interact through an ordinary two-body force and through a momentumdependent two-body “Pauli core” which satisfies, approximately, that $\text{p}{}_{\mathrm{ij}}\text{r}{}_{\mathrm{ij}}\text{≧ξ}\text{h}\text{?}$, where ξ is a dimensionless constant. A form for the Pauli core is presented. The ordinary two-body force has been adjusted to fit bulk properties of nuclei and to reproduce that moment of nucleon nucleon scattering cross sections which is relevant to hydrodynamics. The parameters of the forces are given.     

K+ production in a cascade model for high-energy nucleus-nucleus collisions

The K⁺ production is studied for the p + NaF, Ne + NaF, Ne + Pb systems at 2.1 GeV/A in the frame of a 3-dimensional cascade model. Owing to the small elementary production cross sections, the K⁺ production is calculated perturbatively. Two kinds of production processes are introduced: baryon-baryon collisions leading to three-particle final states, and pion-nucleon collisions leading to two-body final states. The time evolution of the two processes is studied. The integrated K⁺ cross sections are in good agreement with the experimental data. The contribution of the πN induced mechanism is of the order of 25% for Ne + NaF, but increases with the size of the system. Scaling properties are discussed. A simple rescattering model is used to calculate the invariant cross section for the Ne + NaF case. Good agreement with experiment is obtained, except at forward angles.     

Collisions in zero temperature Fermi gases

We examine the collisional behavior of two-component Fermi gases released at zero temperature from a harmonic trap. Using a phase-space formalism to calculate the collision rate during expansion, we find that Pauli blocking plays only a minor role for momentum changing collisions. As a result, for a large scattering cross section, Pauli blocking will not prevent the gas from entering the collisionally hydrodynamic regime. In contrast to the bosonic case, hydrodynamic expansion at very low temperatures is therefore not evidence for fermionic superfluidity.     

Pauli blocking of collisions in a quantum degenerate atomic Fermi gas.

We have produced an interacting quantum degenerate Fermi gas of atoms composed of two spin states of magnetically trapped 40K. The relative Fermi energies are adjusted by controlling the population in each spin state. Thermodynamic measurements reveal a resulting imbalance in the mean energy per particle between the two species, which is a factor of 1.4 at our lowest temperature. This imbalance of energy comes from a suppression of collisions between atoms in the gas due to the Pauli exclusion principle. Through measurements of the thermal relaxation rate we have directly observed this Pauli blocking as a factor of 2 reduction in the effective collision cross section in the quantum degenerate regime.     

Nucleus-nucleus collisions: Intrinsic motion with external correlations

A consistent treatment of the relative and intrinsic motion which goes beyond the mean-field approach allows to include the fluctuations of the time-dependent mean field for the intrinsic as well as for the relative motion. Starting with the v. Neumann equation for the total density matrix, we derive a modified equation for the intrinsic many-body density matrix. This equation is used to obtain the quantum kinetic equations for the one-body density matrix and the two-body correlator. In the time-dependent single-particle basis, the occupation numbers change in time due to a collision term originating from residual two-body interactions which account for equilibration, and due to the fluctuations of the external mean field. The relations to TDHF with collision term are discussed. Special attention is paid to the conditions for a diabatic evolution of the single-particle states and to finite size effects which play an important role to make two-body collisions operative in finite nuclei.     

Particle-Number Conserving Calculation for Low-Lying Excited High-K Multi-Quasiparticle Bands in 172,174Hf

Using the particle-number conserving method for treating the cranked shell model,the microscopic mechanism of the variation of the kinematic moments of inertia with rotational frequency ω for the rare-earth deformed nuclei ^172,174Hf is investigated. The observed J⁽¹⁾ and angular momentum alignment are reproduced satisfactorily in the PNC calculation,in which no free parameters are involved. The PNC analysis shows that the difference between the variations of J⁽¹⁾ with ω for the high K multi-quasiparticle bands and for ground state band is mainly due to the Pauli blocking effect of high j intruder orbitals near the Fermi surface.     

Collisional properties of cold spin-polarized metastable neon atoms

We measure the rates of elastic and inelastic two-body collisions of cold spin-polarized neon atoms in the metastable 3P2 state for 20Ne and 22Ne in a magnetic trap. From particle loss, we determine the loss parameter of inelastic collisions beta=6.5(18) x 10(-12) cm(3) s(-1) for 20Ne and beta=1.2(3) x 10(-11) cm(3) s(-1) for 22Ne. These losses are caused by ionizing (i.e., Penning) collisions and occur less frequently than for unpolarized atoms. This proves the suppression of Penning ionization due to spin polarization. From cross-dimensional relaxation measurements, we obtain elastic scattering lengths of a=-180(40)a(0) for 20Ne and a = +150(+80)(-50)a(0) for 22Ne, where a(0)=0.0529 nm.     

Secondary Collision and the Enhancement of the K+π+ Ratio in the High Energy Heavy-ion Collision

The enhancement of K⁺/π⁺ ratio in the high energy heavy-ion collision is believed to be a possible signature of the quark gluon plasma.Based on the Participant Nucleon Model and the concept of the formation time of secondary particles,the K⁺/π⁺ ratio in the central collision of Si(14.5GeV/c) and Au are calculated by Monte Carlo simulation.The following secondary collisions are considered.πN→K⁺Y、ππ→KK and the single charge exchange reaction between pions and nucleons.The calculation results show that the increased K⁺/π⁺ ratio caused by these secondary collisions is not enough to explain the experimental data observed by the E802 group at BNL.     

Two-body collisions and time dependent Hartree-Fock theory

The time-dependent Hartree-Fock (TDHF) theory is generalized in order to include the effect of two-body collisions (i.e. the residual interaction). This is achieved by adding a collision integral into the TDHF equations, similar to the one ordinarily used in the Boltzmann equation. It is shown, that two-body collisions arise from the imaginary part of the effective interaction between two nucleons whereas the Hartree-Fock field is associated to the real part of the same interaction. There is thus no double counting when the collisions are added to a single particle field. Various approximations for the collision integral are discussed and their accuracy evaluated. Special effort is made in order to obtain conserving approximations. It is shown that for discrete fields, energy as well as momentum conservation is achieved by off-shell scattering processes. In the light of a previous paper, it is argued that two-body collisions should dominate the irreversible processes above some critical energy (roughly 200 MeV per nucleon). Below this energy the irreversible effects due to the single particle field and the collisions are expected to be of the same order of magnitude.     

Two Electron Transfer and Stabilization in Slow O^6＋ and Rare-Gas Collisions

The stabilization ratios R for double-electron transfer, i.e., the cross section ratios of true double capture to total double-electron transfer, are measured in O^6＋ ＋He, Ne and Ar collisions at 6 keV/u. A high R value about 68% is obtained for the He target, while for the Ar target, the R value is only 8%. The high R value for the He target is due to the significant direct population of the （2l, nl′ ） configurations with high n. For the Ar target, the （quasi）symmetric configurations （3l, nl′） lead to the much lower R value. Neglecting the core effects, the O^6＋ ion can be taken as a bare ion C^6＋ except the occupied ls shell, and then the measured R values are compared with previous experimental results of C^6＋ projectile ions at Ne and Ar target, while the occupied ls shell for the C^6＋ ＋He collisions. similar impact velocity. It yields good agreement with the O^6＋ ＋He system results in a higher R value than that in