Simulation of ion propagation in the microbeam line of CENBG using GEANT4

For more than five years the use of microbeam setups for the irradiation of biological samples has opened a new field of investigation in the study of radiobiological effects at low doses. Since 1998, a single ion irradiation system has been developed on the microbeam line of CENBG. Compared to the already existing systems, based on collimated beams, the use of a focused microbeam gives the advantage of a faster irradiation procedure, since the beam can be positioned onto the targeted cells by means of a fast electrostatic deflection system. Single cells irradiation requires a precise control of the position of the incident ions on target, with a spatial resolution of a few microns. All the components of the microbeam line must be designed in order to minimize the spatial dispersion of the beam: single ion transmission detector, collimators used along the beam line, exit window... To understand and to control the different processes of ion diffusion which can occur all along the beam line is thus a crucial point. For this, a reliable beam transport simulation tool is required. For more than 20 years nuclear physicists have used the GEANT code to simulate particle–matter interaction. Its most recent version, GEANT4, with an object-oriented architecture, allows to simulate different components of a beam line, considered as objects that can be inserted into the code. The beam line and the detectors geometry can be easily implemented. Moreover, the simulation code can be interfaced with computer-assisted design systems and numerical analysis software packages. In this article, the first attempt to use GEANT4 to simulate components of a microbeam line with protons and alphas of a few MeV will be presented.