| All living organisms are made of cells. The cell is the fundamental unit of life. There exist all kinds of motion and transport process extensively both between and inside cells. They play very important role for various life activities. At the same time, there are a great deal of transport phenomena in spatial environment in which the organism lives, namely all kinds of ionization radiation, which are key effect for evolution and diversity of species. But, over-radiation may cause pathological changes, for example, cell death, gene mutation and cancer et al. To study the transport mechanism in scale of cell is of important significance to understand life and protect the organisms' health. We have studied some problems qf two aspects in past several years.To study the physical and chemistry mechanism of radiation damage to a cell is one focus of the study of basic theory in radiation biology and biology physics. It is a multidisciplinary research of the nuclear physics, biology, chemistry and medicine. It is necessary for low dose radiation research, health in outer space and radiation protection et al. At the same time it is basic and precursor research for cancerous therapy of heavy ion. The most important theoretical model for the study of radiation damage is track structure model, which is based on the physical data and use Mote Carlo method to simulate the transport of charged particle in medium and give the spatial distribution of non-elastic events with the energy deposit in the scale of nanometer and evolution with time in the scale of Pico second.Cell is a highly non-homogeneous media and the interaction between particles with cell is a highly nonlinear dynamic problem. Water is the major constituent of organism and is homogeneous media, so as the first step one is to study the interaction between radiation and water (from water vapor to water liquid), and then put the DNA in water. Even this kind of work is very difficult and complicated which started from 70's of the last century. So far, track structure model is still at the development stage, within this model media is still water vapor, and the cutoff energy is lOeV, in which the interaction due to abundant low energy secondary electrons are neglected. Such electrons, even at energies well belowionization thresholds, can induce substantial yields of single- and double-strand breaks in DNA, which are caused by rapid decays of transient molecular resonance localized on the DNA's basic components. The research is blank in our country, so we have spent a lot of time and vigor to learn the track model code M0CA15 of GSF and improved it on two aspects: firstly, incident energy of the cross section data used in simulation are fixed, which is not convenient. So, we adopt the cross section data with variable energy. Secondly, the cutoff energy of secondary electrons is too high (10 eV). We have developed own program appropriate for low energy electron and proton, and have considered the interaction of low energy electron (cutoff energy is leV) firstly. At present, we have begun to learn the code TRAX of GSI, which can simulate almost all particles. However, the cutoff energy of second electron is still 10eV.The accuracy of Mote Carlo method depends on detail of the cross section data, which include elastic and inelastic scattering, singly and doubly differential ionization cross sections et al. Data for materials such as DNA and proteins are scare, as measurements are either very difficult or not available. Water is always a good approximation in radiobiology. We have spent a lot of time to obtain all kinds of experimental and theoretical data, and compiled part codes of electron cross-section and most of proton cross-section. Using these tools we have accomplished the woks as follows.1, Using own code we have simulated the track structure of low energy electrons (with minimum energy of leV) in water with Monte Carlo method, taking into account inelastic processes such as ionization, excitation, attachment and auto-ionization caused by super-excitation, and the... |
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