Nuclear interactions of 160 MeV protons stopping in copper: A test of Monte Carlo nuclear models

To estimate the influence of nuclear interactions on dose or biological eff ect one uses Monte Carlo programs which include nuclear models. We introduc e an experimental method to check these models at proton therapy energies. We have measured the distribution of charge deposited by 160 MeV protons st opping in a stack of insulated copper plates. A buildup region ahead of the main peak contains approximate to 20% of the total charge and is entirely due to charged secondaries from inelastic nuclear interactions. The accepta nce for charged secondaries is 100%. Therefore the data are a good benchmar k for nuclear models. We have simulated the stack using GEANT with two nucl ear models. FLUKA agrees fairly well with the measurement but GHEISHA, desi gned for much higher energies, does not. The experimental method will work for many other materials, including insulators. Therefore it can also be us ed for light nuclei. (C) 1999 American Association of Physicists in Medicin e. [S0094-2405(99)00312-0].