Dissipative processes in peripheral heavy ion collisions at Fermi energies

Abstract

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 18 O (35MeV/A) + 9 Be( 181 Ta) at forward angles. We decompose the experimental velocity distributions empirically into two contributions: a direct, 'breakup' 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 deexcitation needs to be considered. We conclude, that such reactions are of interest to study the equilibration mechanism in heavy ion collisions

Isospin effect in peripheral heavy-ion collisions at Fermi energies

“…The de-excitation of primary fragments moves the spectra to the light mass region. It has been investigated that the peripheral nucleus-nucleus collisions have the advantage for creating the neutron-rich isotopes [26]. Shown in Fig.…”

“…The de-excitation of the primary fragments moves the spectra to the light mass region. It has been found that the peripheral nucleus-nucleus collisions have the advantage of creating neutron-rich isotopes [31]. Figure 4 shows a comparison of the effects of the different symmetry energies on the fragment distribution in the symmetric reaction of 136 Xe+ 136 Xe at an incident energy of 20 MeV/nucleon, with the impact parameters of 8-10 fm.…”