Shielding Effects In Proton-Halo Nuclei Fusion Reactions

Heavy ion fusion reaction is not only the unique way for super heavy element synthesis,but also an important method to study the nuclear structure,nuclear properties and nuclear reaction mechanism.The halo nuclei,as a kind of weakly bound nucleus with a exotic structure,it's specific dynamic behavior in the nuclear reaction process cause the concern more and more.One of hot topics is the fusion reaction caused by halo nuclei,because it is closely related to astronuclear synthesis,and can provide one new approach for landing the ”island of stability”.Because of charged valence proton,the reaction dynamic mechanism proton-halo nuclei is more complex and exotic than the one of neutron-halo nuclei.For example,the fusion cross sections of proton-halo nuclei is not enhanced as that of neutron-halo nuclei.One of supposition to explain this phenomenon is that the proton-halo nuclei is polarized so that the valence proton is shielded by the core.In this thesis,by using the Improved Quantum Molecular Dynamics(ImQMD)model,the dynamic mechanism of near barrier fusion reaction by proton-halo nuclei17 F has been investigated,and the shielding effect of valence proton has been studied with emphasis.The main works and the findings include:1.For the special halo structure of proton-halo nuclei,the sample method of ImQMD has been modified to obtain the initial nuclei of17 F with good properties.And a so-call ”spherical shell constrain” has been introduced to keep the stable halo of17 F.By these improvements,the model can be used to study the proton-halo fusion reactions.2.By using the ImQMD model,the near barrier fusion reactions of17F+208Pb?17F+40Ca have been simulated,and the microscopic dynamic mechanism has been investigated.It is found that there are indeed the shielding effect of valence proton during the17F+208Pb fusion processes,and the shielding effect is enhanced with the decrease of distance of projectile and target nuclei in the late stages of the reaction.3.The potentials between the projectile and target in the reactions of17F+208Pb and17F+40Ca in the two extreme case,i.e,valence proton being shielded or unshielded,have been compared.It is found that,the barrier in the case with valence proton being shielded is lower than one in the case with valence proton being unshielded,that would cause the suppression of the fusion cross sections.And it is found that the potential of17F+208Pb-16O+208Pb and17F+40Ca-16O+40Ca,with statical factors being removed,are very close to each other,that is one possible reason leading the similar fusion excitation function of these two groups of reaction systems.