K. Schmidt

DYNAMICAL EVOLUTION OF THE 197Au + 197Au SYSTEM AT 15 MeV/NUCLEON

Collisions of a very heavy 197Au + 197Au system have been studied at an energy of 15 MeV/nucleon with the aim to investigate a possible change of the energy dissipation mechanism from one-body dissipation (presumably dominating at low excitation energies) to two-body dissipation. The experiment was carried out in 4π geometry using the CHIMERA multidetector array. A class of ternary events satisfying nearly complete balance of mass numbers was selected. Preliminary results suggest that the selected ternary events represent mostly prompt ternary partitions of the colliding system, in which the lightest fragment is quite massive. In the light of theoretical predictions of Cârjan, Sierk and Nix this result may imply that the observed ternary reactions are driven by the two-body dissipation mechanism already at 15 MeV/nucleon.

TERNARY REACTIONS IN 197AU + 197AU COLLISIONS REVISITED

Ternary events originating from the 197Au + 197Au reaction at 15 MeV/nucleon, studied by using the multidetector array CHIMERA at LNS Catania, have been collected in almost complete 2π range of the forward hemisphere of CHIMERA thus extending the angular range of our previously reported preliminary data. Energy- and time calibrations for heavy fragments at large angles were supplemented with an analysis of coincidence events of binary strongly damped reactions. Contrary to the previous preliminary results, the new complete data clearly show presence of sequential fission processes in which one of Au-like nuclei undergoes fission after re-separation of the primary binary system. Mechanism of these two types of reactions observed in our data, sequential fission reactions and prompt ternary processes, are presently studied using comparisons with predictions of the stochastic BNV model of Baran, Colonna and Di Toro and the QMD model of Łukasik.

Isospin Effects in Heavy‐Ion Collisions: Some Results From CHIMERA Experiments At LNS And Perspectives With Radioactive Beams

CHIMERA is a 4π multidetector for charged particles available at Laboratori Nazionali del Sud (INFN‐LNS). A new method to measure the time scale of the emission of nuclear fragments is described, together with some applications in the field of the isospin dynamics of heavy‐ion collisions. Competition between fusion‐like and binary reactions near the energy threshold for nuclear multifragmentation is discussed. Opportunities are pointed out to use the detector at low and intermediate energies using the kinematical‐coincidence method.

Isospin effects in projectile‐like dynamical fission for 112,124Sn+58,64Ni reactions at 35 AMeV

A quantitative comparison regarding absolute cross sections associated to Statistical and Dynamical Fission processes in the 124Sn+64Ni and 112Sn+58Ni collisions experimentally investigated at 35 AMeV beam energy using multi‐detector CHIMERA is presented. It results that Dynamical Fission process is about two times more probable in the neutron rich 124Sn+64Ni system than in the 112Sn+58Ni neutron poor one. The observed difference could indicate an influence of the entrance channel Isospin (N/Z) content on the reaction mechanisms.