Theoretical Investigation On Elastic Electron Scattering From Some Unstable Nuclei

High-energy elastic electron scattering is the most powerful tool for investigating nuclear charge and proton density distribution.In the past,experimental research on electron-nucleus scattering was only carried out for stable nuclei or long-lived unstable nuclei,due to the limitation of technology for making targets.With the development of radioactive nuclear beam facilities,experimental research on electron scattering off highly unstable nuclei has been put into agenda.Besides,parity violating electron scat-tering,which takes into account weak interaction between electrons and nuclei,can be used to study nuclear neutron density distribution.According to the above mentioned development in electron-nucleus scattering,we do research on two aspects by combin-ing nuclear relativistic mean-field theory and relativistic partial-wave analysis method.On one hand,we systematically study nuclear charge density distribution and electron-nucleus elastic scattering.On the other hand,we study the difference between neutron and proton density distribution of some isotopic nuclei,and their parity violating elastic electron scattering.The research on the first aspects is the main topic of this thesis,and it mainly contains three parts.First,we study nuclear charge density distribution and elastic electron scattering for some nuclei along the isotopic chain(N=8 and 50)and the isotonic chain(N=8).Taking the oxygen isotopic chain(Z=8)for example,according to the numerical results from nuclear relativistic mean-field theory,with neutron number increasing,the center and tail parts of the nuclear charge density decrease gradually,while the surface charge density at r?3 fm increases gradually.Because of the regular change of charge density distribution,there exists obvious and regular change in the corresponding differential cross section of elastic electron scattering off these isotopic nuclei.The first scattering minimum shifts inward and upward when neutron number increases.Similar results are also obtained in the research of tin isotopic nuclei.The difference between nuclear charge density distributions of the N=8 isotonic nuclei is very distinct,and the differen-tial cross section of elastic electron scattering off these nuclei shifts inward and upward clearly as a whole with the proton number increasing.Second,we investigate the proton halo nuclei and their elastic electron scattering.According to the results from relativistic mean-field theory,the charge density distribu-tions of the ground state and the first excite state of 17F are both more extended than that of the ground state of 16O.However,compared with the elastic electron scattering off 160,the first scattering minimum for the ground state of 17F without proton halo shifts inward and upward,while the first scattering minimum for the first excited state of 17F with proton halo shifts outward and downward.The same conclusion is also obtained from the investigation of elastic electron scattering off three different configurations of 18Ne.As a result,elastic electron scattering can be used to determine whether a nucleus has proton halo structure.Third,we study the central depression of charge density distributions of 46 Ar and 44S and their elastic electron scattering.The neutron-rich nuclei,46Ar and 44S,have center-depressed nuclear charge distributions,because the energy levels of proton 2s1/2 and 1d3/2 states are inversed.The calculation with the relativistic mean-field theory also supports the above opinion.The differential cross sections of elastic electron scattering off the center-depressed nuclei are worked out with the relativistic partial-wave analysis method.The minimum of scattering form factor shifts upward and inward when the central charge density distribution is depressed down,which coincides with the results analyzed using three-parameter Fermi distribution.The research on the second aspect is about parity violating electron scattering.To begin with,we compare the numerical results with plane wave Born approximation,relativistic Eikonal approximation and relativistic partial-wave analysis method.And then,we systematically study the parity violating electron scattering off oxygen,tin and lead isotopic nuclei.Taking the oxygen isotopic chain for example,we carefully analyze the results of 12,16,20,24O.In terms of the calculation with relativistic mean-field theory,the proton and neutron density distributions of 160 are almost the same,and the difference between proton and neutron density distributions of 12,24O is very obvi-ous.According to the results of the parity violating electron scattering using relativistic partial-wave analysis method,the parity violating asymmetry curve for 16O vibrates with small amplitude,while the parity violating asymmetry curves for 12,24O vibrate with very large amplitude.We also study parity violating electron scattering off tin and lead isotopic nuclei,and similar results are also obtained.With the difference be-tween the neutron and proton density distribution becoming larger,the parity violating asymmetry curve vibrates with larger amplitude.Therefore,parity violating electron scattering can be used to identify the difference between the proton and neutron density distributions,and to get precise neutron density distribution.