| With the development of technology,the application of radiation has been deeply involved in science and technology and daily life.Most applications of radiation are based on ionizing radiation,that is,radiation particles can ionize atoms in the medium and generate various radiation effects,such as radiation damage,radiation chemical effect and radiation biological effect.For a long time,the study of radiation effect has been based on the statistical average physical quantity produced by the interaction between radiation and matter,such as absorbed dose,while neglecting the secondary process of the interaction between radiation and matter in the actual interaction process,among which the most important one is the generation of secondary electrons due to ionization.The generation of secondary electrons directly leads to the change of atomic and molecular states,which is the basis for the detailed study of chemical and biological effects of irradiation.Based on this background,this paper uses Monte Carlo method to model and analyze the process of generating secondary electrons by ionizing particles in the medium,summarizes the physical model of the process of generating secondary electrons and implements the software,writes a practical software tool and does the simulation calculation under the typical medium conditions.Firstly,elastic scattering and inelastic scattering are considered in the physical process.Mott model and Rutherford scattering model are used comprehensively in the elastic scattering,and the experimental data are used to perform numerical fitting for the low energy elastic scattering cross section of water molecules.Different models of inelastic cross section are used for different shells.The dielectric function model based on the first Born approximation is used for the outer shell,and the binary encounter approximation model is used for the inner shell.For water molecules,electron attachment and dissociation are also considered.The main achievements of this thesis include: 1)The research results on the secondary electron generation process in literatures,existing software and the theoretical framework to describe the process are summarized and a physical model with both accuracy and practicability is given.2)For water molecules,a more detailed theoretical modeling and cross-section data calculation method are carried out.Mott model and Rutherford scattering model are used comprehensively for elastic scattering,and the experimental data are used for numerical fitting of low energy elastic cross-section of water molecules.Different models of inelastic cross-section are used for different shells.The dielectric function model based on the first Born approximation is used for the outer shell,and the binary encounter approximation model is used for the inner shell.The attachment and dissociation process of electrons are also considered.3)A set of Monte Carlo simulation method for secondary electrons is proposed,and the calculation program is written in C++.The program chooses a random number generator with long cycle while using Open GL to do visual post-processing.In the energy range of low energy electrons,continuous slowing approximation is used to improve the calculation efficiency of the program.4)Verify the physical model and the program,including cross-section data,continuous energy model and program comprehensive verification.The program is used to simulate the secondary electron correlation results of Al medium,and compared with the experimental data to verify the feasibility of the program.5)As an attempt to apply the program to the biological effects of radiation,the generation and transport of secondary electrons in water are mainly simulated,and the energy spectrum,yield and spatial distribution of secondary electrons in water are summarized and analyzed.The tool presented in this work could be used in multi-physics modeling of radiation effect in materials by combining with simulation with Molecular Dynamics and Computational Chemistry,and may give a new insight in the research of biological radiation effect... |
