Benchmark Calculations of Neutron Production and Induced Radioactivity for a Proton and a Carbon Therapy Accelerator*

This study intends to predict the scope of neutron production and induced radioactivity for two therapy accelerators in Taiwan: 235 MeV proton and 400 MeV/A carbon ion accelerators. For radiation safety concern, much effort has been put into associated benchmark calculations to ensure the quality of predictions. Two Monte Carlo codes FLUKA and MCNPX were applied to calculate the neutron yield from beam bombardment. In addition, FLUKA was used to study the target activation by examining isotope inventory, residual activity, remnant dose rate, and their time behaviour. The calculated results were compared with experimental data published in literature. For the proton-induced neutron yield, FLUKA and MCNPX both well reproduce the measured results over the entire neutron energy range and for various emission angles. For the carbon-induced neutron yield, there exist larger discrepancies between calculations and measurements. Regarding activation related calculations, a factor of two or larger differences between calculations and measurements were observed due to some limitations of underlying nuclear models and uncertainties involved in comparisons. For practical considerations in radiation safety, this study can give us guidance and confidence in using these codes for shielding design and activation analysis of particle therapy accelerators.