Response of the Mimosa-28 pixel sensor to a wide range of ion species and energies

Abstract

CMOS pixel sensors, originally developed for High Energy Physics experiments, are also used for space radiation and medical applications as vertex detector. These high spatial resolution sensors can provide accurate particle trajectories, which is necessary in several experiments as cross section measurements. In the present work, the response of the CMOS pixel sensor Mimosa-28 was systematically investigated for different ion beams and energies. A series of experiments was performed to study the number of pixels triggered by an incoming particle as a function of the energy loss in the range 10–14000 keV. The measurements were performed for ion beams used in clinical applications such as protons and carbon ions, but also for heavier particles such as iron ions that are relevant for space radiation research, for energies from 10 MeV/u up to 1 GeV/u. In addition, the spatial energy loss distributions of several ion beams, depending on the particle species and energy, were computed with Monte Carlo simulations. A semi-empirical model, based on thermal diffusion and Coulomb expansion, was developed to reproduce the response of the sensor as a function of the energy loss. Furthermore, the detector was exposed to mixed fields composed of primary ions and lighter nuclear fragments. This study showed that this sensor can be used as an additional tool in conjunction with other detector systems to improve particle identification in large experiments.