[en] This report summarizes the progress on grant No. DE-FG05-89ER40530 during the period April 15, 1990 to February 15, 1991. Our studies of heavy-ion collisions in the framework of ''a stochastic one-body transport model'' has progress in several directions. We developed a method for obtaining approximate numerical solutions of the transport-equation in semi-classical limit, i.e., Boltzmann-Langevin equation, and tested the method in realistic cases of heavy-ion collisions at energies below 100 MeV per nucleon. Some results of the numerical simulations for a head-on collision of ¹²C + ¹²C system is included in this report. Work has also continued on studying the stochastic one-body transport model in a quantal representation, which provides a microscopic basis for a consistent description of dissipation and fluctuation properties of large amplitude collective nuclear motion. The previous derivation of the stochastic one-body transport model was presented within the density matrix formalisam. We generalized this treatment and proposed an alternative derivation of the model by employing the Green's function approach within the real-time path formalism of Keldish. One manuscript has been submitted to Nucl. Phys. A for publication. Two other manuscripts are in preparation for publication. Several seminars and contributed talks were presented at various meeting

[en] In the course of the past few years, the nuclear Boltzmann-Langevin (BL)model has emerged as a promising microscopic model for nuclear dynamics at intermediate energies. The BL model goes beyond the much employed Boltzmann-Uehling-Uhlenbeck (BUU) model, and hence it provides a basis for describing dynamics of density fluctuations and addressing processes exhibiting spontaneous symmetry breaking and catastrophic transformations in nuclear collisions, such as induced fission and multifragmentation. In these standard models, the collision term is treated in a Markovian approximation by assuming that two-body collisions are local in both space and time, in accordance with Boltzmann's original treatment. This simplification is usually justified by the fact that the duration of a two-body collision is short on the time scale characteristic of the macroscopic evolution of the system. As a result, transport properties of the collective motion has then a classical character. However, when the system possesses fast collective modes with characteristic energies that are not small in comparision with the temperature, then the quantum-statistical effects are important and the standard Markovian treatment is inadequate. In this case, it is necessary to improve the one-body transport model by including the memory effect due to the finite duration of two-body collisions. First we briefly describe the non-Markovian extension of the BL model by including the finite memory time associated with two-body collisions. Then, using this non-Markovian model in a linear response framework, we investigate the effect of the memory time on the agitation of unstable modes in nuclear matter in the spinodal zone, and calculate the collisional relaxation rates of nuclear collective vibrations

[en] This report discusses the following topics: Relativistic Boltzmann-Langevin model for heavy-ion collision; K+ production far below free neucleon-nucleon threshold and damping of collective vibrations in a memory-dependent transport model

[en] In order to calculate scalar averages of the product of any number of operators, over a finite number of many particle states, a diagrammatic method is developed. This method is generalized to configuration averages and to fixed isospin averages, and it is found that these averages follow trivially from the results of scalar averages. The scalar and configuration averages of the product of three and four two-body operators are derived. Recent theoretical research has shown that shell model level densities are near normal. Hence the level densities for light nuclei are assumed Gaussian and the centroid and widths of these shell model level densities with fixed angular momentum projection and isospin are calculated and tabulated for many light nuclei using these averaging techniques and an approximate formalism for the angular momentum dependence. The core (¹⁶O) is assumed inert; the valence nucleons are assumed to move in an average field, but are confined to the (1s,0d,0f/sub 7/2/) orbitals, and interact via realistic effective two nucleon interactions. Both the energy and angular momentum dependence of these Gaussian level densities are compared, near the proton threshold, to those of the Fermi level densities used in the compound heavy ion reactions. The general conclusion is that the Fermi level density rise too rapidly with energy and underestimate the level densities of higher angular momentum states. The shell model level densities are used to extract ground state energies and low excitation spectra for light nuclei and these are compared to empirical values. Predicted Yrast lines agree quite well with recent experimental data on high angular momenta states in ²³Na and ²³Mg. (Diss. Abstr. Int., B)

[en] This progress report studies of fluctuation processes in nuclear collisions discusses the following topics: quantal effects on growth of instabilities in nuclear matter; collisional damping of giant resonances in a non-Markovian approach; and medium-modified interaction induced by fluctuations

[en] This report summarizes the progress on grant No.FG05-89ER40530 during the period March 1, 1993 to April 30, 1994. By extending our previous work on the fluid dynamical treatment of the nuclear collective motion, we deduced from the Boltzmann-Langevin (BL) model a set of transport equations for N collective variables and calculated the associated transport coefficients. Work has also continued on investigating the relation between the BUU model and the BL model for the average evolution. The principle investigator spent a fruitful summer (1993) at LBL, where in collaboration with J. Raindrop, we developed a numerical method for simulating the stochastic evolution of the phase-space density near local equilibrium. Two papers have appeared in Phys. Rev. C and Nucl. Phys. A, two papers have been accepted for publication, both in Nucl. Phys. A, and two manuscripts have been submitted to Z. Phys. A for publication. Several seminars/contributed talks were given at various meetings and an invited talk was presented at the NATO Advanced Study Institution Hot and Dense Matter, Bodrum/Turkey

[en] Investigations of various aspects of heavy-ion collisions were carried out in the framework of the Boltzmann-Langevin Model (BLM). In a previous work, by projection the BLM onto a collective space, a memory-dependent collective transport model was reduced. This model was applied to thermal fission to investigate the influence of the memory effects on the fission dynamics. Some results of the calculations are presented. In addition a reduction of the relativistic BLM to a two-fluid model was carried out, and transport coefficients associated with fluid dynamical variables was carried out. Then this model was applied to investigate equilabration and fluctuation properties in a counter-streaming nuclear fluid

[en] This report summarizes the progress on grant No. FG05--89ER40530 during the period August 15, 1989 to April 15, 1990. Most of the activity during this period was foucsed on providing a detailed description of a one-body transport model (stochastic BUU), and developing a method for obtaining approximate numerical solutions of the equation of motion. The stochastic BUU model goes beyond the standard BUU by incorporating dynamical fluctuations into the equation of motion. Therefore, it opens up a possibility for a dynamical description of multifragmentation processes in nuclear collisions at intermediate energies. Results of the first numerical calculations for head-on collisions of ¹²C + ¹²C and ⁴⁰Ca + ⁴⁰Ca systems at various energies are included in this report. The preliminary calculations have already revealed the substantial effects of fluctuations on the production mechanism of the intermediate mass fragments, and on the rare particle production mechanism in nuclear collisions. Work has also continued on establishing the connection between the one-body transport model and the collective transport models familiar from previous studies

No abstract available

[en] In order to incorporate fluctuations into the extended TDHF, a new approach is proposed. The evolution of the single-particle density is considered as a ''generalized Langevin process'' in which the correlated part of the two-body collisions acts as a ''random force''. In the semi-classical approximation, the correlation function of the random force is calculated. A possible algorithm for the numerical solution is discussed