Study Of Microscopic Optical Potentials For Nucleus-Nucleus Scattering

The study of a nucleus-nucleus microscopic optical potential (MOP) is one of the fundamental subjects in nuclear physics. It is an important theoretical tool for describing the nuclear elastic scattering and studying more complicate reactions, such as collective excitations, break-up reaction, transfer reaction, fusion and fission etc. In particular, it is very important to understand the complex optical potential for composite projectiles from a microscopic point of view not only to understand the relevant reaction dynamics involved but also to develop a practical tool for predicting optical potentials of colliding systems for which the elastic scattering measurement is absent or difficult, such as in the case of neutron-rich or proton-rich unstable nuclei. The development of the radioactive beam facilities in the world offered the possibility to explore new phenomena at the limits of the nuclear stability. The nature of exotic nuclei has excited a great interest from a theoretical point of view, and the microscopic optical potential of an exotic nucleus with nuclei is one of the important issues in the radioactive nuclear beam physics. The purpose of this work is to study microscopic optical potentials of nucleus-nucleus scattering, especially for unstable nuclei from a fundamental theory.The isospin dependent microscopic optical potentials of the nucleon-nucleus scatterings have been obtained in the framework of the DBHF approach, which successfully describe the nucleon-nucleus scattering cross sections and spin observables. Extending this microscopic optical potential to the case for a composite projectile we compute the microscopic optical potential in a folding model and consider the target nucleus just as a scatterer. Applying the MOP we investigate the elastic scatterings off stable nuclei with various composite projectiles, stable nuclei such as , ⁶Li and unstable nuclei, for instance ⁶He, ¹¹Li, ¹¹Be etc. Due to the complexity of nucleus - nucleus collisions a complete microscopic treatment of the collision between two composite nuclei has still not been available. In order to describe the experimental data two normalization factors N_R, N_I are introduced in our calculations. In our study we aim to explore a unified description of the MOP in nucleus-nucleus scatterings and do not expect an accurate fit to the experimental data at the first step. Therefore we did not perform a careful parameters searching. In order to give a reasonable description of the experimental data in differential elastic cross sections a rough adjustment of the two parameters is carried out only by eyes.In comparison with the experimental data it is found that the real part of the MOP in our model is too deeper. This is due to the density effects of the overlap of two Fermi spheres, which has not been treated properly in our folding model. A large reduction factor N_R is required for stable projectiles, for example forα-nuclei scattering, while it is approximately equal to 1.0 for a loosely bound nucleus ⁶He. It may indicate that the effects of the overlap between two Fermi spheres are quite different in stable and unstable nuclei. The imaginary part of the DBHF G matrix in our model takes account of only the lowest order particle-hole excitations. The inelastic processes in nucleus-nucleus scatterings are much more complicated, which include many possible inelastic channels, excitations, break up etc. Certainly the imaginary part of the MOP obtained in our model is much too shallow. A large N_I has to be introduced to reasonably describe the experimental differential cross sections. Obviously, N_I is larger for unstable nuclei, such as for ⁶He, ¹¹Be,¹¹Li and ¹⁷F, and smaller for stable nuclei. This conclusion is also valid for various targets and incident energies. Much more efforts are still required to obtain a parameter free microscopic optical potential of nucleus-nucleus interaction, which would be of value in the description of the nucleus-nucleus scattering, especially for the unstable nuclei.The S-factor of the d(d,γ)αreaction at low energy plays a crucial role in the astrophysics. The value of the S-factor at the region of the astrophysics interest E_c.m. < 20keV is not available experimentally. Therefore theoretical investigations of the S-factor are essential. The electromagnetic radioactive transition in the radioactive capture reaction d(d,γ)αis mainly the electrical quadrupole transition. We have studied the reaction by the direct capture method that allows for the D-state component of the colliding deuterons and the D-state component of ground state wave function of ⁴He. In our theoretical model the wave functions are calculated in Woods-Saxon potentials. A set of parameters of Woods-Saxon's potentials are obtained by reproducing the binding energies of d-d system and d-d elastic scattering phase shifts calculated by the resonating group method (RGM). In comparison of theoretical predictions with the experiments, good agreement can be obtained in the energy range E_c.m. < 3MeV. Due to the lack of experiment data at the energies about 0-20keV a theoretical extrapolation of the S-factor down to the stellar energies is performed. We therefore recommend the value of S (0) = 5.9×10^-6keV·b for the d(d,γ)αreaction. Meanwhile it is obtained that the ratio of D state in the ground state in ⁴He is about 5.4%～13.4%, which agreed with the result 9.89%～16.04% predicted by a modern nuclear force theory.