| Research Abstract |
1. Introduction
Radiation track structure (microscopic spatial distributions of ionization and excitation) obtained by Monte Carlo simulation contributes significantly to research of radiation effects. We have developed new generation track codes for low-energy protons and alpha particles, in which charge exchange processes and nuclear elastic scattering are taken into account.
2.Methods
In the energy range below 0.3MeVu^<-1> for H^+ and He^<++>, neutral or dressed ions such as H^0 or He^+ and He^0 are generated by electron capture. Experimental and theoretical cross sections for all these particles for water molecule were collected and compiled. Secondary electrons ejected by ion impact were traced by the electron code kurbuc developed by ourselves. The reliability of the codes was confirmed by comparing the various physical parameters with the published data
3. Results
Calculated electronic and nuclear stopping powers, ranges and W values agreed with ICRU data within 10% uncertainties. Th
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e codes provided various microdosimetric quantities such as radial dose distributions, restricted stopping powers and lineal energy spectra. These data were in good agreement with the published data.
4. Conclusions
Newly developed low-energy codes, lephist for protons and leahist for alpha particles, are "full slowing down codes", not "track segment code" conventionally used. The impact on the research field of track structure may be large. The effective energy ranges are 1 keV to 1 MeV for protons and 1 keV to 8 MeV for alpha particles. Therefore, these are useful for applications to the mechanistic understanding of radiation effects of neutrons and heavy ions in environment. Track structure identifies the products of H_2O^+, H_2O^+ and e_<sub>^- at the physical stage. These products immediately form the radicals, OH, H, e_<aq>^-, and so on, due to chemical reactions with water molecules. The future objective is to develop an inclusive track structure code including radiation chemistry as a function of time between 10^<-15> and 10^<-6>s. Less
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