Simulation Study On The Generation Of Positrons By Laser Plasma Accelerated Electron Bombardment Of Solid Targets

Since the positron was predicted and discovered in the 1930s,it has been widely used in many fields of nuclear physics,atomic and molecular physics,solid state physics,surface interface physics,materials science,high energy physics,and medical imaging.In many fields,how to obtain a high-quality positron source is the focus of the moment.Radioisotope decays were initially used as positron sources for experiments.In recent years,with the development of experimental techniques,radioisotopes have been used as positron sources to meet the relevant experimental requirements.Based on this,scientists have proposed to generate positrons by bombarding metal targets with high-energy electrons,but this method requires high electron energy.With the development of laser technology and the emergence of high-intensity,high-power lasers,the use of high-energy lasers to bombard solid targets to produce positron beams has become a research focus in related fields.Simulation program is writing based Geant4 for accelerating electron by laser plasma bombardment of solid targets and positron detectors.Then simulates the process of laser plasma accelerating electron bombardment of solid targets to generate positrons.The relationship between superheated electron beam energy,target material,target thickness and positron yield,and the angular distribution and energy spectrum of positrons and other secondary particles are discussed.The paper mainly includes the following two aspects:First,the Monte Carlo simulation software Geant4 was used to construct the physical model,Simulation code for constructing models of superheated electrons react with solid targets and detector models?Part I of Appendix II?,and the laser plasma accelerated electron bombardment of the solid target to generate positrons was systematically studied.Firstly,the effects of different target materials on positron yield were studied.In the simulation experiment,materials such as Al,Ti,Fe,Sn,Ta,Cu,Au and Pb were selected for simulation.The simulation results show that Au is best material.At the same time,compared with the theoretical calculations in the literature,the simulation and calculation results are in good agreement.The effect of the thickness of the metal target on the positron yield is discussed during the simulation.According to the counting of the detector established by Geant4,1cm is the optimal target thickness,and the yield is increased with the thickness of the target.The relationship between the positron yield and the energy of the electron beam is also discussed in the simulation.After fitting the quadratic function,the highest positron yield can be obtained by the function fitting result.In the experiment,it is concluded that the angles of the exiting positrons are concentrated in the range of0-30^o.The positron energy was found to be within 0-30 MeV in the simulation.In the above related physical processes,X-rays with strong penetrating power are generated.It is an easy method to reverse the information of a solid target with information carried by X-rays.A model of Geant4-based high-purity germanium detector was designed for this purpose,and a high-purity germanium detector was tested with ⁶⁰Co radioactive source for simulation detection.To verify reliability,the data results were compared to the standard data provided by the GEM-C5060.After comparison,the measured FWHM is 1.9 keV,and the detection efficiency is 15%.Basically meet the data provided by the manufacturer.Second,due to the action of the super-strong laser and the gas target,the target atoms become ions,and the ions have high energy due to the acceleration of the super-strong laser.Based on the above work,and by writing a simulation code for the action of gas target ions and solid targets?Part II of Appendix II?.Since the ions are of higher quality under the same conditions,the information of the energy spectrum and angular distribution of the positrons generated by the ion bombardment of the solid target is simulated.When the Xe⁵⁴⁺ion with energy 50 MeV/u interacts with a solid target,the energy of the positron is mainly concentrated at 100 MeV.There are many types of secondary particles,including those produced by nuclear reactions.Since the heavy ions emerging after the target carry a lot of information,the relative amounts of different ionized ions of the target ions are recorded in the simulation.The simulation results show that Si¹⁺accounts for the most.At the same time,the momentum distribution of the solid target ions is simulated.