Radiation shielding design and residual radioactivity assessment for the beam dump at XiPAF

BackgroundThe Xi'an 200 MeV proton application facility (XiPAF) is planned for upgrade and transformation into a versatile experimental facility for both proton and heavy-ion applications, requiring comprehensive radiation protection design for operational safety.PurposeThis study aims to develop a radiation-safe beam dump design ensuring compliance with operational dose limits during operation and minimizing post-irradiation residual doses.MethodsFirstly, the neutron yield characteristics of different target materials were analyzed using FLUKA Monte Carlo simulations to determine the optimal core material with low neutron production. Then, a composite structure beam dump was designed with polyethylene as the target core material, iron as the main shielding material, and borated polyethylene as the outer shielding layer. Finally, shielding performance was quantified via ambient dose equivalent rate mapping at critical locations, and residual dose decay kinetics were modeled for three operational scenarios: 1-h, 1-d, and 1-w continuous irradiation at maximum beam intensity of 1.3×1010 protons per second.ResultsThe computational results show that the maximum ambient dose equivalent rates at the rear and transverse sides of the beam dump are 4.2 mSv·h-1 and 3.2 mSv·h-1 respectively, both below the design limit of 5.5 mSv·h-1. Compared to traditional graphite core, polyethylene demonstrates approximately 75% lower upstream dose while maintaining equivalent downstream shielding performance. Analysis of residual dose under the three operational scenarios shows consistent decay patterns, with all cases reaching the dose constraint of 2.5 μSv·h-1 after 2~3 h cooling time.ConclusionsThe polyethylene-core composite beam dump design provides effective radiation protection for the XiPAF facility upgrade, with significantly reduced neutron backscattering compared to conventional graphite targets. The residual radioactivity analysis indicates that facility access can be safely permitted within 2~3 h after beam shutdown for all typical operational scenarios. These results provide practical reference for radiation protection design of beam dumps at similar intermediate-energy proton accelerator facilities.