Speaker
Description
An analysis of the energy, mass and angular distributions of the binary reaction products in the heavy ion collisions allows us to construct the dynamics of the complete fusion and quasifission mechanisms. The competition of the different possible mechanisms depends on the beam energy and impact parameter of collision, mass asymmetry, orientation angles and nuclear shell structure of the colliding nuclei.
It is important to stress that the angular momentum of the dinuclear system (DNS) formed at capture of projectile by target nucleus plays decisive role in the evolution of the mass and charge distribution between its fragments. Since intrinsic fusion barrier $B^*_{\rm fus}$, fission $B_f$, and quasifission $B_{\rm qf}$ barriers, as well as the excitation energy $E^*_{\rm DNS}$ depend on the angular momentum. Theoretical analysis of the incomplete fusion mechanism and experimental data demonstrating the possibility of the overlap of the mass and charge distribution of the fusion-fission and quasifission proves that complete fusion occurs by multinucleon transfer from light nucleus to heavy one in heavy ion collisions. The DNS can evolve up to compound nucleus due to the complete fusion or it breaks up two fragments by the incomplete fusion and quasifission mechanisms. Recently, we have proved that the incomplete fusion occurs during multinucleon transfer from the light nucleus to the heavy one in collisions with the large orbital angular momentum. In this case, the centrifugal force increases due to small values of the moment of inertia of the DNS consisting of alpha particle and conjugate nucleus during its evolution. As a result, the centrifugal force causes a hindrance to complete fusion and at the same time breaks this very asymmetric system. The multinucleon transfer from heavy nucleus to light one leads to quasifission of the DNS. Our theoretical studies showed the the mass distributions of the fusion-fission and quasifission products may overlap. In this case quasifission products can be considered as fusion-fission products and as a result, the experimental value of the fusion cross section is overestimated when fusion-fission products are used to estimate fusion cross section. The separation of the pure experimental fusion cross section is ambiguous task when takes place overlap of the mass distributions of those above mentioned process. The overlap of the mass distributions of the products formed in different reaction channels depends on the mass asymmetry of the entrance channel and beam energy in the heavy ion collision.
The nature of the overlap of the mass distributions of the fusion-fission and quasifission products is discussed on the base of the theoretical results obtained at the analysis of the deviations of the mass distributions of the fusion-fission products observed in the experiments performed for collisions of nuclei different mass asymmetry in the entrance channel. The role of the orientation angles of the axial symmetry axis of the colliding nuclei, beam energy and orbital angular momentum on the mass distribution of the quasifission products is demonstrated by the analysis of the theoretical results calculated to interpret the corresponding experimental data of the mass distribution of the fusion-fission products mixed with the quasifission products. The role of the entrance channel in formation of the evaporation residues cross sections is discussed.