Projectile fragmentation at Fermi energies with transport simulations

Projectile fragmentation at Fermi energies is an important method to produce radioactive beams for the study of isospin asymmetric nuclear matter. Fragmentation is usually parametrized successfully by empirical phase space models. In this contribution we apply a microscopical method, semiclassical transport theory, to study in detail the reaction mechanism of the fragmentation process. We apply it to experimental data of 18O on 181Ta at E/A = 35 MeV measured in Dubna. We calculate consistently the excitation energy of the primary fragments and take into account their decay by a statistical model. It is found that the dissipative part of the fragment spectra is well described by transport theory. However, there are in addition important direct and collective contributions

Study of projectile fragmentation of 40Ar on 9Be target at 40A MeV

Section II. Experimental Investigations of Nuclear Reactions Mechanism

Dissipative processes in 18O + 9Be and 18O + 181Ta reactions at Fermi energies

A study of peripheral nuclear collisions at Fermi energies with transport models is presented. It is motivated by experiments devoted to studying of isotopic yields in the reactions 18O on 9Be and 181Ta at E/A = 35 MeV measured at very forward angles. The data show a two-component structure, one centered at beam velocity (“direct component”) and another at lower velocities (“dissipative component”). It is shown that the transport calculations describe the general features of the dissipative component of the reaction. In our calculations we take into account the evaporation of the excited, primary projectile-like residues due to statistical decay. This improves the comparison of the results of the calculations with experiment. We find substantially different behavior of the dissipative component in the reactions with light and heavy target

Study of projectile fragmentation of 40Ar on 9Be target at 40A MeV

Section II. Experimental Investigations of Nuclear Reactions Mechanism

Competition of break-up and dissipative processes in peripheral collisions at Fermi energies

Heavy ion collisions in the Fermi energy regime may simultaneously show features of direct and dissipative processes. To investigate this behavior in detail, we study isotope and velocity distributions of projectile-like fragments in the reactions 18O (35 MeV/A) + 9Be(181Ta) at forward angles. We decompose the experimental velocity distributions empirically into two contributions: a direct, ‘break-up’ component centered at beam velocity and a dissipative component at lower velocities leading to a tail of the velocity distributions. The direct component is interpreted in the Goldhaber model, and the widths of the velocity distributions are extracted. The dissipative component is then successfully described by transport calculations. The ratio of the yields of the direct and the dissipative contributions can be understood from the behavior of the deflection functions. The isotope distributions of the dissipative component agree qualitatively with the data, but the modification due to secondary de-excitation needs to be considered. We conclude that such reactions are of interest to study the equilibration mechanism in heavy ion collisions