FRAGMENTATION BARRIERS OF TOROIDAL AND BUBBLE NUCLEI

With an improved Boltzmann-Uehling-Uhlenbeck model, the deformation en ergy surfaces in reactions leading to the formation of toroidal and bu bble nuclei are examined for central Mo-92+Mo-92 collisions. We found that the potential maximum, or the fragmentation barrier, occurs at ti mes close to the times when these exotic shapes are formed. However, d ue to the dynamics of large amplitude compression and expansion, the f ragmentation barriers are significantly higher than those estimated fr om the liquid-drop models.