D. Sperber

Nucleon emission from the interface of two colliding heavy ions

Abstract Energy and angular distributions of nucleons emitted in the early stages of intermediate energy heavy ion reactions are calculated. It is assumed that these nucleons originate in a hot region which is created near the contact point of touching spheres. Since the emission occurs during the very early stages of the reaction this model is applicable for both fusion and strongly damped collisions. Contributions from central to peripheral collisions are included. The model has been used for the study of the reaction 197 Au + 16 O and the results compare well with experiment.

The role of asymmetry on critical and limiting temperature

Abstract The critical temperature of infinite nuclear systems and the limiting temperature of finite nuclear systems are found to be strongly sensitive to neutron-proton asymmetry.

The rarefaction of oblate shaped nuclear matter in heavy-ion collisions

Abstract We examine the disintegration stage of a hot zone in a high energy heavy-ion collision using hydrodynamics. We consider the initial non-homogeneously compressed matter to have an oblate shape. An approximate solution to the hydrodynamic equations is obtained by solving two coupled non-linear differential equations for the semiaxes of the boundary. We show that the boundary passes through a spherical shape and finally ends in a prolate configuration as the rarefaction proceeds. We apply the model to heavy-ion reactions to calculate angular distributions. We compare our theoretical results with experiments selected for central collision for the reaction C + Ag and O + Ag at energies about 200 MeV/nucleon. Good agreement between theory and experiment is obtained. Comparison with experiment allows estimating the ratio between the major and minor axis of the original oblate shape. It is shown that both non-homogeneity and shape asymmetry lead to enhanced forward and backward ejection of matter in the c.m. frame.

Role of Thermal Fluctuations in a Classical Dynamical Model for Fission

We present a dynamical model for the motion of the fissioning nucleus in the classically allowed region after penetrating the barrier up to the scission point. The thermal fluctuations associated with the shape degrees of freedom are incorporated. The model has been applied to determine the mass and kinetic energy distributions for the spontaneous fission of 252Cf.

ANALYSIS AND INTERPRETATION OF ISOMER RATIOS.

Abstract Isomer ratios in (n, γ) reactions have been analysed. The analysis shows that this ratio is very sensitive to a small admixture of quadrupole radiation. It also shows that either the strength of the quadrupole radiation is larger than predicted by the single-particle model or that the strength of the dipole radiation is overestimated by this model.

The role of deformation and transfer in the analysis of strongly damped collisions

Abstract It is shown that the wide spectrum of final total kinetic energies and the correlation between energy loss and the FWHM of the charge distribution for the reactions Kr + Bi at 712 MeV and Xe + Bi at 1130 MeV can be well accounted for by (a) introducing deformation phenomenologically using different entrance and exit channel potentials, and (b) treating transfer as a random process.

The Role of Deformation, Thermal Fluctuations and Single Particle Transfer in Strongly Damped Collisions

A dynamical model for strongly damped collisions with the inclusion of deformation, single particle transfer and thermal fluctuations is presented. We show that all these aspects are essential to account for the experimental data.

Stability and temperature of a hot compressed zone in heavy-ion collisions☆

Abstract It is shown that for heavy-ion reactions over 30–50 MeV/ A a hot zone can disintegrate yielding a high nuclear multiplicity. The temperature of the hot zone is calculated within the liquid drop model, where the volume term is determined using mean field theory. The dependence of the nuclear surface tension on temperature and density is also evaluated.

Radiation of pions from an expanding fireball

Abstract Using arguments from statistical mechanics we derive expressions for the pion multiplicities and spectra in high energy heavy ion reactions. We show that pions emerge during the early stage of the hydrodynamical expansion and that their energy distributions reflect mainly the temperature of the surface.

A suggestion for a parameter free model of strongly damped collisions

Abstract A parameter free model of strongly damped collisions is outlined. The proton and neutron drifts are determined by solving two coupled differential equations based on Einstein relations. The mass and charge variance are determined from an effective interaction time and an effective neck area both obtained from a dynamical calculation. We examine the reaction Xe + Bi at 1130 MeV. For all partial waves the theoretically predicted ratios of charge drift to charge variance agree very well with those obtained from recent experimental data.