The Distortion of Energy Deposit Distribution of ¹²C Ions in Water

The transport process of 12C ions in water was studied with SRIM code and Geant4 toolkit. The SRIM results indicate that the transverse diffusion of 12C ion beam causes distortion of energy deposit along the beam direction. The distortion becomes more notable as the transverse diffusion increases. The simulation results of Geant4 indicate that the influence of secondary fragments on energy deposit distribution would be the main factor causing the distortion in higher energy range. In the region adjacent to the beam line where the contribution from 12C ions dominates, the contributions from secondary fragments are ignorable. The further from the beam axis the region locates, the larger the contributions from secondary fragments, until the contributions from secondary fragments exceed that of 12C. Among all the secondary fragments, the contributions of H, He and B ions are mostly notable. It is also found that some positron-emitting secondary fragments could be very useful for PET.