This paper presents a comprehensive study of phonon-mediated quasiparticle (QP) poisoning in superconducting qubit arrays, focusing on the effects of ionizing radiation and strategies for mitigating these effects. The authors use the G4CMP simulation tool to model the dynamics of phonons and QPs following a particle impact, comparing their results with experimental measurements. They demonstrate that their model accurately captures the spatial and temporal characteristics of QP poisoning for various configurations of phonon downconversion structures. The study highlights the challenges posed by correlated errors caused by ionizing radiation, which generate QPs in the qubit electrodes and reduce qubit coherence. The authors describe a numerical simulation strategy that models the phonon and QP dynamics after an impact, showing how these QPs can cause errors across a significant portion of the qubit array. They also present experimental data on QP charge-parity switching rates, which are used to assess the effectiveness of different phonon mitigation strategies. The paper discusses the impact of various back-side metallization configurations on QP poisoning, showing that devices with phonon downconversion structures, such as Cu islands, significantly reduce the QP density and recovery time. The authors simulate the QP poisoning footprint following a gamma-ray impact, demonstrating that effective phonon mitigation can confine the QP poisoning region to a small area, allowing for faster recovery. The study also compares the recovery timescale of QP poisoning in different device configurations, showing that devices with effective phonon mitigation recover much faster than those without. The authors conclude that their modeling approach provides valuable insights into the design of future superconducting qubit arrays and phonon-based sensors of rare events. The results highlight the importance of phonon mitigation strategies in improving the reliability and performance of superconducting quantum processors in the presence of ionizing radiation.This paper presents a comprehensive study of phonon-mediated quasiparticle (QP) poisoning in superconducting qubit arrays, focusing on the effects of ionizing radiation and strategies for mitigating these effects. The authors use the G4CMP simulation tool to model the dynamics of phonons and QPs following a particle impact, comparing their results with experimental measurements. They demonstrate that their model accurately captures the spatial and temporal characteristics of QP poisoning for various configurations of phonon downconversion structures. The study highlights the challenges posed by correlated errors caused by ionizing radiation, which generate QPs in the qubit electrodes and reduce qubit coherence. The authors describe a numerical simulation strategy that models the phonon and QP dynamics after an impact, showing how these QPs can cause errors across a significant portion of the qubit array. They also present experimental data on QP charge-parity switching rates, which are used to assess the effectiveness of different phonon mitigation strategies. The paper discusses the impact of various back-side metallization configurations on QP poisoning, showing that devices with phonon downconversion structures, such as Cu islands, significantly reduce the QP density and recovery time. The authors simulate the QP poisoning footprint following a gamma-ray impact, demonstrating that effective phonon mitigation can confine the QP poisoning region to a small area, allowing for faster recovery. The study also compares the recovery timescale of QP poisoning in different device configurations, showing that devices with effective phonon mitigation recover much faster than those without. The authors conclude that their modeling approach provides valuable insights into the design of future superconducting qubit arrays and phonon-based sensors of rare events. The results highlight the importance of phonon mitigation strategies in improving the reliability and performance of superconducting quantum processors in the presence of ionizing radiation.