Simulation of the Residual Activity Induced by High-Energy Heavy Ions

Quantification of residual activity is an important issue for high-power accelerator facilities like the Facility for Antiprotons and Ion Research (FAIR). While beam losses of 1 W/m are at present accepted for proton machines as a tolerable level for ensuring "hands-on" maintenance, the beam-loss tolerances for high-energy heavy-ion accelerators have not yet been quantified. The Monte Carlo particle transport codes FLUKA and SHIELD were used to simulate the irradiation of copper and stainless steel by different ions (¹H, ⁴He, ¹²C, ²⁰Ne, ⁴⁰Ar, ⁸⁴Kr, ¹³²Xe, ¹⁹⁷Au, and ²³⁸U) with energies typical for FAIR machines. Copper and stainless steel were chosen as common materials for accelerator structures. The isotope inventory contributing >90% to the total residual activity does not depend on the projectile species; it depends only on the target material and projectile energy. The activity per watt induced by a 1 GeV/u heavy ion is lower than the activity per watt induced by a 1-GeV proton. A tolerable beam-loss level for a 1 GeV/u ²³⁸U beam was found to be [approximately]5 W/m.