Study On The Ground State Properties Of Neutron-rich Exotic Nuclei By The Complex Momentum Representation Method

With the continuous development of radioactive nuclear beam devices,the study of neutron(proton)-rich exotic nuclei far away from the?-stability line has become one of the hottest topics in nuclear physics.The weakly bound of valence nucleon far away from the?-stability line and the multiple coupling of continuous states form some exotic phenomena,such as halo,skin and the change of magic number and so on.The single-particle resonant states play an important role in the formation of exotic phenomena.In this thesis,we combine the complex momentum representation(CMR)method with the non-relativistic,relativistic mean field theory(RMF)and the relativistic point coupled(RMFPC)models,respectively.The ground state properties of neutron-rich exotic nuclei are studied by these methods,and the contribution of single-particle resonant states to the exotic properties,especially the halo phenomena.The thesis includes the following four parts:First,the CMR method can used to describe bound states,resonant states and continuous spectrum on the equal footing,but also narrow resonant states and broad resonant states.In view of the advantages of the CMR method,this method has been further developed to study the deformed nuclei.¹⁹C is a neutron-rich exotic nucleus,its ground state behaves as a one-neutron halo.In order to understand this exotic phenomenon,we apply the CMR method to explore the ground state properties of ¹⁹C,and obtain the single-particle levels structure.It is found that the last valence neutron of ¹⁹C occupies the level 1/2[211],which is mainly composed of s_1/2 component.This supports that ¹⁹C is a s-wave one-neutron halo nucleus,and reveals the physical mechanism of ¹⁹C halo formation.Secondly,since the CMR method has achieved success in studying the physical mechanism of ¹⁹C halo structure,it encourages us to use the CMR method to predict halo candidates.Therefore,we use this method to study exotic structure of neutron-rich nuclei in the medium mass region.The energies of the bound and resonance states as a function of the ?₂ are obtained,and a clear shell structure is shown.The occupation probabilities of major configurations and density distribution of the valence neutron orbitals are given.The results show that ⁷⁷Fe,⁷⁵Cr and ⁵³Ar have halo structures,which are the candidate nuclei for experimental exploration of halo phenomena in heavier nuclei.Thirdly,the CMR method is extended to the relativistic mean-field(RMF)framework,and the RMF-CMR-BCS method is developed using the BCS approximation to consider the pair correlations.The exotic structures of the even-even neutron-rich Ca,Ni,Sn and Pb isotopes are systematically studied by CMR method,and the effects of the single-particle resonant states for the neutron halo and neutron shell are further discussed.Lastly,the relativistic point-coupling model(RMFPC)is one of the most accurate micro theoretical models.The RMFPC model is combined with the CMR method with pairing correlations considered by BCS approximation,deal with the coupling between bound states and resonant states,which is developed the RMFPCCMR-BCS theory.The RMFPC-CMR-BCS theory is used to study the ground state properties of the even-even Ce isotopes.We found that halo and giant halo in the Ce isotopes near the neutron drip line.It is in agreement with the calculation results of RHB theory.