A monolithic silicon telescope for hadron beams. Numerical and experimental study of the effect of ΔE detector geometry on microdosimetric distributions

A monolithic silicon telescope consisting of a surface ΔE detector 2 μm in thickness coupled to an E detector about 500 μm in thickness made out of a single silicon wafer was recently proposed for the microdosimetric characterization of hadron beams. This work discusses the study of the effect of the geometrical structure of the ΔE detector on microdosimetric distributions measured by the silicon device in hadron beams. Two different devices, i.e. a single-diode ΔE detector 1 mm² in sensitive area and a ΔE detector geometrically segmented in micrometric cylinders, were irradiated at different phantom depths with 62 AMeV carbon ions in the same experimental conditions. In order to reproduce and deeply analyze the experimental results, a detailed numerical study based on Monte Carlo simulations was carried out through the FLUKA code version 2012, a recent release able to transport heavy ions at energies lower than 100 AMeV (the older lower transport limit) by exploiting the new Boltzman Master Equation model. The comparison between microdosimetric distributions measured by the two different detectors highlighted discrepancies at low lineal energies. Those differences, not reproduced by simulations, are probably due to charge sharing between the ΔE electrodes and the surrounding guards of the segmented device. (author)