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A time-dependent microscopic approach of the fission process based on the constrained HFB approach with the Gogny force and the Hill and Wheeler configuration mixing method is described. Recent results concerning fragment distributions (mass, kinetic and deformation energies) and other fragment observables in 238U obtained with such an approach are presented and discussed. [ABSTRACT FROM AUTHOR]

Theoretical results for giant resonances in the three doubly magic exotic nuclei 78Ni, 100Sn and 132Sn are obtained from Hartree-Fock (HF) plus Random Phase Approximation (RPA) calculations using the D1S parameterization of the Gogny two-body effective interaction. Special attention is paid to full consistency between the HF field and the RPA particle-hole residual interaction. The results for the exotic nuclei, on average, appear similar to those of stable ones, especially for quadrupole and octupole states. More exotic systems have to be studied in order to confirm such a trend. The low energy of the monopole resonance in 78Ni suggests that the compression modulus in this neutron-rich nucleus is lower than the one of stable ones. [ABSTRACT FROM AUTHOR]

This contribution summarizes the predictions obtained in the domain of superheavy nuclei from self-consistent microscopic calculations employing the Gogny force. Results concerning shell gaps, fission barriers and stability against alpha-decay are recalled. Recent work involving α-decay chains in odd nuclides is also presented and discussed. [ABSTRACT FROM AUTHOR]

A microscopic theory for the decay of a compound nucleus is presented which is formulated in the spirit of transport theories. Its basic physical assumption is the existence of two time scales, a rapid one concerning the creation of intrinsic excitations and a slow one controlling the change of the nuclear shape. This fact is used in the derivation of an equation of motion for the reduced density by applying the so-called Markov approximation. A canonical distribution of the system with regard to the intrinsic excitations at a given shape is assumed as an approximation and a temperature T(q, t) depending on the nuclear shapes and time t is defined so as to render the canonical distribution as realistic as possible. [ABSTRACT FROM AUTHOR]

Abstract: We formulate a microscopic theory of the decay of a compound nucleus through fission which generalizes earlier microscopic approaches of fission dynamics performed in the framework of the adiabatic hypothesis. It is based on the constrained Hartree–Fock–Bogoliubov procedure and the Generator Coordinate Method, and requires an effective nucleon–nucleon interaction as the only input quantity. The basic assumption is that the slow evolution of the nuclear shape must be treated explicitly, whereas the rapidly time-dependent intrinsic excitations can be treated by statistical approximations. More precisely, we introduce a “reference density” which represents the slow evolution of the nuclear shape by a reduced density matrix and the state of intrinsic excitations by a canonical distribution at each given shape of the nucleus. The shape of the nuclear density distribution is described by parameters (“generator coordinates”q), not by “superabundant” degrees of freedom introduced in addition to the complete set of nucleonic degrees of freedom. We first derive a rigorous equation of motion for the reference density and, subsequently, simplify this equation on the basis of the “Markov approximation”. The temperature T which appears in the canonical distribution is determined by the requirement that, at each time t, the reference density should correctly reproduce the mean excitation energy at given values of the shape parameters q. The resulting equation for the “local” temperature must be solved together with the equations of motion obtained for the reduced density matrix . [Copyright &y& Elsevier]

Two-dimensional Hartree-Fock-Bogoliubov (HFB) calculations have been performed from spherical shapes to large deformations with constraints on axial quadrupole and octupole deformations in 238U, 256–260Fm and 226Th actinides. Scission configurations have then been identified in this subspace of collective coordinates and many nuclear properties of the nascent fragments have been derived, such as deformation, deformation energy or prompt neutron multiplicity. The HFB states have then served as basis states for time-dependent collective calculations based on the Time-Dependent Generator Coordinate Method and the Gaussian Overlap Approximation to derive fission fragment yields. [ABSTRACT FROM AUTHOR]

Low energy fission is described using a microscopic and time-dependent approach. Fission dynamics is derived from the evolution of a collective wave function in the restricted space generated by the quadrupole and octupole collective variables. Propagation is made by use of the Time Dependent Generator Coordinate Method with a basis set of Hartree Fock Bogoliubov states obtained from self-consistent calculations with the Gogny force. Theoretical fragment mass and kinetic energy distributions in actinide fission are presented. First calculations with selected initial states indicate that the main features of experimental mass distributions in 238U are reproduced. The peak-to-valley ratio appears to significantly depend on the parity of the initial state chosen. [Copyright &y& Elsevier]

Abstract: We review the most important experimental results from the first three years of nucleus–nucleus collision studies at RHIC, with emphasis on results from the STAR experiment, and we assess their interpretation and comparison to theory. The theory-experiment comparison suggests that central Au + Au collisions at RHIC produce dense, rapidly thermalizing matter characterized by: (1) initial energy densities above the critical values predicted by lattice QCD for establishment of a quark–gluon plasma (QGP); (2) nearly ideal fluid flow, marked by constituent interactions of very short mean free path, established most probably at a stage preceding hadron formation; and (3) opacity to jets. Many of the observations are consistent with models incorporating QGP formation in the early collision stages, and have not found ready explanation in a hadronic framework. However, the measurements themselves do not yet establish unequivocal evidence for a transition to this new form of matter. The theoretical treatment of the collision evolution, despite impressive successes, invokes a suite of distinct models, degrees of freedom and assumptions of as yet unknown quantitative consequence. We pose a set of important open questions, and suggest additional measurements, at least some of which should be addressed in order to establish a compelling basis to conclude definitively that thermalized, deconfined quark–gluon matter has been produced at RHIC. [Copyright &y& Elsevier]