Most cosmic particles around a detector in space near the Earth are protons. Sometimes, we need to reject the protons to enhance the efficiency of particle experiments. In this study, we try to find the proper thickness of a polystyrene scintillator to reject protons by using a Monte Carlo simulation tool, GEANT4, which is a common tool in high-energy experimental physics. We assume that a detector is shielded by a cylindrical shell polystyrene scintillator. Then, we inject protons, with energies from 150 MeV to 10 GeV into the polystyrene scintillator. The multiple scattering between a proton and the polystyrene molecules causes the protons to lose energy and finally stop. By calculating the energy of proton lost in the scintillator, we could obtain information on the shielding ability of polystyrene against cosmic protons.

Keywords: Proton, Cosmic ray, Polystyrene, Simulation method