Description of heavy ion reactions with medium dependent forces

Abstract

The collision between two nuclei is calculated in the Quantum Molecular Dynamics (QMD) approach for C-C and Nb-Nb reactions using a collision term for the nucleon-nucleon cross section which is determined in the nuclear medium using the Brueckner G-matrix with the appropriate Pauli operator and the self consistent single particle energies for the densities of the projectile and the target at the collision point of the two nucleons. The QMD approach is very similar to the Vlasov-Uehling-Uhlenbeck or Boltzmann-Uehling-Uhlenbeck approach, but taking into account the finite extension of the wave packet representing a nucleon in position and momentum space. Usually one uses in the collision term a constant (40 mb) or the free nucleon-nucleon cross section. Using a local density approximation the Bethe-Goldstone equation is solved for two colliding nuclear matters of which the densities are determined by the local densities obtained in the QMD approach at the collision point of the two nucleons inside the nuclear medium. Comparing the momentum transfer in transverse and longitudinal direction and the number of emitted particles calculated with the G-matrix cross section and the isotropic constant cross section (40 mb) we find for this inclusive data only minor differences between the results in the C-C collision, but larger ones for the Nb-Nb case. The double differencial cross section for charge particle emission in the C-C reaction at E lab = 84 MeV/n is described in good agreement with the data.