Microscopic transport theory of heavy-ion collisions

Transport equations of the Fokker-Planck type are derived from a master equation for deeply inelastic collisions. Using the method of spectral distributions, the transport coefficients are calculated for symmetric fragmentations. Analytic formulas are given for the memory time, for the energy-drift coefficient and for the diffusion coefficients which correspond to the excitation of the fragments and the transfer of nucleons. These expressions contain parameters of the basic interaction matrix elements only, which describe excitations and transfers. Agreement with experimental data is obtained for reasonable values of these interaction parameters. Production cross-sections are predicted for superheavy nuclei in the deeply inelastic collisions U+U and U+Cf.     

Analysis of relaxation phenomena in heavy-ion collisions

The transfer of mass, as well as the dissipation of relative kinetic energy and relative angular momentum in deeply inelastic heavy-ion collisions are studied as functions of time. Based on the determination of a parametrized deflection function from the experimental angular distributions, a classical model for the calculation of the mean interaction time as a function of initial relative angular momentum is presented. The method allows to include also those processes which correspond to long interaction times. The model is applied to determine mass transport coefficients from experimental mass (or element) distributions. The resulting mass drift and diffusion coefficients are accurate within less than 30% and compare well with the systematics obtained from the microscopic transport theory. The energy loss as function of interaction time is consistent with the following picture: Fast dissipation of the radial part of the kinetic energy accompanied by the loss of angular momentum with a larger relaxation time.     

Strong coupling effects in the transport equation for deeply inelastic heavy-ion collisions

The appearance of strong coupling effects in the transport equation for deeply inelastic heavy-ion collisions is examined in the framework of a one-dimensional model. An analytical solution for the Greens function shows that in a deeply inelastic collision the system is in the strong-coupling regime for the bulk of the interaction. An analytical method is presented for evaluating the transport coefficients which can equally be applied to the three-dimensional case. The transport coefficients and cross sections are calculated and the dependence of the results on the parameters of the underlying random-matrix model is displayed.     

Electron distribution function in a weakly ionized He-Hg mixture

The electron energy distribution functions for He-Hg mixture in a uniform electric field are calculated for differentE/N and relative mercury concentration? from fundamental cross-section data. The Boltzmann equation is applied considering the elastic and inelastic collisions of electrons with neutrals of the both components. From these distributions and elastic collision cross-section (for He and Hg) drift velocity, diffusion coefficient and mean electron energy are computed. The electron energy losses in elastic and inelastic collisions over the considered region of the parameters are discussed.     

Nucleon tunnelling model of mass diffusion in deep inelastic heavy ion collisions

We derive a simple expression for the mass diffusion coefficient in deep inelastic collisions, based on a proximity formulation of nucleon tunnelling. The predicted value of the coefficient is consistent with empirical data. The mass diffusion coefficient has a negligible dependence on excitation energy in the physically interesting domain.     

Transport Coefficients for Inelastic Maxwell Mixtures

The Boltzmann equation for inelastic Maxwell models (IMM) is used to determine the Navier–Stokes transport coefficients of a granular binary mixture in d-dimensions. The Chapman–Enskog method is applied to solve the Boltzmann equation for states near the (local) homogeneous cooling state. The mass, heat, and momentum fluxes are obtained to first order in the spatial gradients of the hydrodynamic fields, and the corresponding transport coefficients are identified. There are seven relevant transport coefficients: the mutual diffusion, the pressure diffusion, the thermal diffusion, the shear viscosity, the Dufour coefficient, the pressure energy coefficient, and the thermal conductivity. All these coefficients are exactly obtained in terms of the coefficients of restitution and the ratios of mass, concentration, and particle sizes. The results are compared with known transport coefficients of inelastic hard spheres (IHS) obtained analytically in the leading Sonine approximation and by means of Monte Carlo simulations. The comparison shows a reasonably good agreement between both interaction models for not too strong dissipation, especially in the case of the transport coefficients associated with the mass flux     

Nucleon transport processes in fission and heavy ion reactions

The nucleon exchange process between two nuclei in close proximity and its application to an explanation of fragment mass and charge distributions in fission and in heavy ion deep inelastic collisions are reviewed. An analysis of the measured correlations between the energy loss from relative motion and the fragment mass and charge variances in the heavy ion deep inelastic collisions is presented. The recent data on fragment mass and charge variances as a function of the fragment kinetic energy in thermal neutron induced fission of²³⁵U, lends added support to the hypothesis that the nucleon transport process plays a similar role both in fission and in heavy ion deep inelastic collisions.     

Closed-form quantal description of inelastic heavy ion scattering

The amplitude for inelastic heavy ion scattering, given by the distorted-wave theory for excitation of low-lying collective states, is evaluated in closed form. Use is made of the Austern-Blair relation and of other approximations appropriate for strongly absorptive interaction to express the inelastic partial-wave amplitude entirely in terms of the elastic S-matrix elements in the initial and final channels. The resulting formulae display explicitly the various contributions to the transition amplitude, whose superposition gives rise to the variety of interference patterns observable in the angular distributions and excitation functions of inelastic heavy ion scattering. It is shown that, as for elastic scattering, the dominant mechanism in inelastic heavy ion collisions near and above the Coulomb barrier is diffractive scattering of Fresnel type.     

Murrell-Sorbie势下He-HCl碰撞体系微分散射截面的研究

根据在CCSD(T)/aug-cc-pVQZ理论水平下计算的He-HCl相互作用能数据,作者采用Murrell-Sorbie势函数形式拟合了He原子与HCl分子相互作用的各向异性势,并与其它势模型进行了比较;然后采用公认的精确度较高的CC近似方法计算了He-HCl碰撞体系的微分散射截面,总结了非弹性微分散射截面的变化规律.研究表明:采用拟合的各向异性势计算的微分散射截面与实验结果符合得很好.拟合势不但表达形式简洁,而且较好地描述了He-HCl系统相互作用的各向异性特征;利用碰撞体系分子间势的量子化学从头计算结果,可解决势能参数难以确定的问题.对进一步研究原子与分子相互作用的机制有一定的参考价值.     

Cold inelastic collisions between lithium and cesium in a two-species magneto-optical trap

We investigate collisional properties of lithium and cesium which are simultaneously confined in a combined magneto-optical trap. Trap-loss collisions between the two species are comprehensively studied. Different inelastic collision channels are identified, and inter-species rate coefficients as well as cross-sections are determined. It is found that loss rates are independent of the optical excitation of Li, as a consequence of the repulsive Li^*-Cs interaction. Li and Cs loss by inelastic inter-species collisions can completely be attributed to processes involving optically excited cesium (fine-structure changing collisions and radiative escape). By lowering the trap depth for Li, an additional loss channel of Li is observed which results from ground-state Li-Cs collisions changing the hyperfine state of cesium. Received 28 December 1998 and Received in final form 16 February 1999     

Formation of excited singly charged barium ions in collisions of slow electrons with barium dibromide molecules

The method of extended crossing beams is used to study inelastic collisions of slow electrons with barium dibromide molecules. The resulting optical emission spectrum contains only the spectral lines of the singly charged barium ion. At an exciting electron energy of 100 eV, the cross sections of dissociative excitation for nine spectral lines of BaII are measured; for all these lines, the optical excitation functions over an electron energy range of 0 to 100 eV are recorded. The possible channels of the dissociative excitation of BaII are discussed.     

Theoretical estimates for the production of transuranium elements in heavy-ion collisions

A thick target experiment of the U+U reaction at 7.5 MeV/u is analyzed within the diffusion model for dissipative heavy-ion collisions. Cross sections for the production of superheavy elements as well as probability distributions of excitation energies and spins as function of fragment charge are estimated. The influence from changes of incident energy and projectile-target combination is studied.     

Energy dependent nucleus-nucleus potential in heavy ion collisions

The energy dependence of the real part of the nucleus-nucleus potential is evaluated in the proximity picture of Blocki et al. using Seyler-Blanchard two-body effective interaction. This energy dependent potential is used to study the fusion excitation functions and deep inelastic collisions. These results are compared with those calculated with the energy independent proximity potential and it is observed that the energy dependence of the potential does not affect the results significantly except for the reduction of the high energy fusion cross sections.     

On a density matrix equation for atomic systems subject to an external radiation field interaction and collision processes

Approximations are examined which are necessary for a density matrix equation of Rautian's form describing the interaction of a gas medium with an external radiation field by considering collision processes between active atoms as well as active and perturber atoms. The collision integrals of the kinetic density matrix equation calculated by the Bogolyubov method involve exitation processes, inelastic and elastic collisions. The features of phase- and velocity changing collisions are discussed by specializing the collision terms. Some phenomenological collision models for velocity changing collisions are examined and conditions for their validity given.     

Dynamical study of the Cs<Superscript>+</Superscript>(<Superscript>1</Superscript>S<Subscript>0</Subscript>)+Mg(3 <Superscript>1</Superscript>S<Subscript>0</Subscript>) non adiabatic collision system in the few keV energy range

The dynamics of collisional processes between Mg atoms and caesium ions is studied using the hemiquantal (HQ) approach with special attention to the collisional channels leading to Mg(3 ¹P) and Cs(6 ²P) states, for which the corresponding emission excitation functions have been previously measured in our laboratory. The radial and angular non-adiabatic couplings between the manifold of quasimolecular states have been determined using an ab initio configuration interaction calculation. The cross-sections for the different channels, as a function of the laboratory collisional energy, are compared with experimental values. The dynamical calculations indicate that, for the inelastic processes considered, the range of relevant impact parameters is small, active collisions being of the head-on type. .     

A microscopic calculation of angular and energy distributions of light fragments in deeply inelastic heavy-ion reactions

A random-matrix model for the form factors connecting channels corresponding to high intrinsic excitation energy of either fragment is used to calculate energy-averaged cross sections in deeply inelastic heavy-ion reactions. The distribution of the form factors is determined microscopically. The calculation yields differential cross sections without any fit parameters. Results for Kr- and Bi-induced reactions are compared with the data.     

Fission of238U induced by136Xe for energies close to the Coulomb barrier

Excitation functions and angular distributions have been measured for fission of²³⁸U induced by¹³⁶Xe ions with bombarding energies between 4.5 and 5.9 MeV/N. Structures expected theoretically as characteristic for Coulomb fission have not been observed. The Q-value of ?(7.5±1.0) MeV measured for bombarding energies below 4.7MeV/N, however, appears to be compatible with inelastic scattering (e.g. Coulomb excitation) rather than subcoulomb transfer followed by fission. The total kinetic energy of deep inelastic events at 5.9 MeV/N is consistent with the current knowledge about mass diffusion, but also (for the highest excitation energies) with a fast fission process in the presence of the projectile.     

Self-consistent modelling of X-ray preionized XeCl-laser discharges

In this theoretical work a 0-D model for a self-sustained X-ray preionized XeCl-laser discharge is presented. The model is self-consistent in the sense that it simultaneously solves, contrarily to the usual decoupling procedure, the Boltzmann equation for electrons, the kinetic equations for excited and ionic species, the equations for the electrical circuit and the laser photon density. It includes a rather complete kinetics of HCl(v) vibrational excitation, dissociation and dissociative attachment. The influence of electron collisions with excited species and of e-e Coulomb collisions on the plasma parameters and transport coefficients is discussed. Some evidence of the non-stationary equilibrium between the electron distribution and the reduced electric field E/N is given. Results of the model are compared with experimental ones corresponding to a XeCl-laser discharge driven by a L-C inversion circuit. The model predicts well the main trends for the variation of the laser energy in a large range of experimental conditions. The discrepancy between experiment and model for absolute values of the laser energy is discussed.