Giant Dipole Resonance In Proton Capture Reactions And Studies On ?-delayed?Two? Proton Emission From ²³Si

Nuclear physics,as an important discipline for human beings to understand the essence of the world,has always been the frontier of material science.It has a significant impact on the survival of humans and the development of civilization,and it is also an important factor determining the comprehensive national strength and international status of a country.However,there are still many doubts about the structure,properties and nuclear dynamics of nuclei.Therefore,a large number of researchers at home and abroad put their best efforts to study nuclear physics theoretically and experimentally,mainly focusing on the equation of state of nuclear matter,nuclear many-body dynamics,radioactive ion beam physics,nuclear astrophysics and so on.In the study of nuclear matter equation of state and nuclear many-body dynamics,Isovector Giant Dipole Resonance?GDR?is one of the hotspots in recent years.GDR can be considered as the relative collective oscillation between proton and neutron spheres in the nucleus.It is one of the most pronounced features in the excitation of nuclei and almost all nuclei throughout the whole chart of nuclides have this collective motion mode.The energy spectrum parameters of GDR can be used to extract the most reliable information about the structure and dynamic properties of nuclear many-body systems,which thus makes it as an effective probe for the study of nuclear properties.The parameters of GDR spectrum mainly include the peak energy,the strength and full width at half maximum?FWHM?.The peak energy is directly related to the masses of nuclei and the equation of state of nuclear matter,especially the symmetry energy.The strength accounts for a large percentage of the energy-weighted sum rule.The FWHM is related to the spin,temperature and excitation energy of the nucleus.In particular,it is still controversial whether the resonance width is saturated at higher temperature,which is also the main object of our research.In the first part of this thesis,we used the extended quantum molecular dynamics model?EQMD?to study the GDR of ¹²C,²⁸Si,⁴⁰Ca,and ⁶⁸Ni in proton capture reactions ¹¹B?p,??¹²C,²⁷Al?p,??²⁸Si,³⁹K?p,??⁴⁰Ca,and ⁶⁷Co?p,??⁶⁸Ni.The systematic properties of the peak energy,the strength and FWHM were drawn.The results show that the peak energy of GDR is negatively correlated with the mass number of fused nuclei in different reaction systems,so is its decrease degree.The strength increases first and then decreases with the increase of proton incident energy.Compared with proton incident energy,the FWHM is more dependent on the temperature of fused nuclei,and almost remains unchanged when the temperature is lower than 1.5 MeV.When the temperature is within 1.5MeV-3.5 MeV,the FWHM increases sharply with the increase of temperature,which is consistent with the previous theoretical and experimental results.When the temperature is higher than 4 MeV,our calculated results support the idea that the FWHM of GDR saturates at higher excitation.In radioactive ion beam physics,exotic nuclei far from the?-stable line exhibit many properties different from stable nuclei.Especially in the study of their decay modes,a lot of information about nuclear structure,such as energy level position,energy level width,energy level density,spin,parity,and nuclear mass,can be obtained,which expands the research field of traditional nuclear physics and complements the theory of shell model.These decay modes are also important information to nuclear astrophysics studies.It is one of the current research hotspots.²³Si is the lightest proton-rich nucleus of T_z=-5/2.It may have many exotic decay modes,such as?-delayed proton,two-proton,three-proton and proton-?-particle decay.Its decay properties are essential bases for the calculation of its mass and play an important role in verifying the shell model theory.In 1986,Langevin et al.first observed ²³Si through the fragmentation reaction of ⁴⁰Ca.After that,Blank et al.studied the decay of ²³Si for the first time in 1997,and obtained the half-life and the charged-particle energy spectrum of ²³Si.By comparing the results with the calculations of shell model,they concluded that?-delayed two-proton decay occurred in ²³Si.However,they did not investigate?-ray spectrum,so they could not directly prove this phenomenon from the experimental results,which is also the motivation and main purpose of our experiment.The experiment was performed on the facility of Radioactive Ion Beam Line in Lanzhou.A primary beam of 75.8 MeV/u ²⁸Si impinged on a 1980?m ⁹Be target.²³Si was generated by projectile fragmentation method.Then the decay phenomena of ²³Si were studied by implantation-decay method using silicon detector array and high-purity germanium detector array.The charged-particle energy spectrum and?-ray energy spectrum of ²³Si were obtained.Finally,the branching ratio of?-delayed particle decay and the half-life of ²³Si?40.17±1.86?ms were obtained,which are both consistent with the results of Blank et al.In addition,we have found a new energy peak of?p decay at 3811 keV and also its corresponding new decay level.Through two-proton and?-ray coincidence,the?-delayed two-proton decay from ²³Si to the first excited state of ²¹Na has been confirmed directly for the first time.However,due to the limitation of statistics and detection efficiency,same as the results of Blank et al,we cannot conclude that ²³Si has more exotic decay modes,such as?-delayed three-proton and proton-?-particle decay.