Theoretical Study of the Reaction Mechanism of Low Energy Heavy Ion Collisions

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1. We studied the effects of nuclear intrinsic degrees of freedom on the heavy ion fusion reactions. Our main results are: (1) Nuclear vibrational modes of excitation largely enhance the fusion cross section at sub-barrier energies. (2) This enhancement is mainly due to the large potential renormalization. (3) The extra-ordinarily large enhancement for the <^(74)Ge> and <^(74)Ge> collision suggests that a large deformation of <^(74)Ge> is induced in the unified system. (4) The dimension of the coupled-channels equations can be considerably reduced for heavy systems. (5) A geometrical interpretation holds for the fusion reaction in the limit of adiabatic tunneling.2. We derived the retarded friction functions for the energy and the angular momentum dissipation due to nuclear surface vibrational excitation in low energy heavy ion collisions. We then clarified the dependence of the dissipation mechanism on the incident energy.3. We derived a formula, which determines the lag of microscopic degrees of freedom in quantum tunneling in multi-dimensional systems. This method was then applied to the muon catalyzed d-t fusion, and showed that the mon-adiabaticity reduces the sticking probability of the muon to the fusion synthesized alpha particle by about 30 %.4. We applied Weidenmuller's new statistical theory to nuclear pre-equilibrium process. The result agreed with that of Agassi et al. in the limit of weak coupling, but differes in the strong coupling limit. Also, the level density was calculated by this method.5. We calculated the elastic scattering and the absorption cross sections using a time dependent mean field theory (TDMF).6. We showed that the <root> E constraint in the surprisal analysis of heavy ion reactions arises from a constraint to the exciton number. Also, we calculated the level density for the exciton model by taking into account the angular momentum.