Investigation of Radiation-Induced Mechanical Degradation in Beryllium: A Comprehensive Study of High Energy Proton Irradiation Effects

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Abstract
Beryllium is widely used as a beam-window material in particle accelerators because its low atomic number and high specific stiffness minimize beam scattering while maintaining good thermal resistance. However, energetic proton irradiation alters its microstructure and degrades its mechanical performance. Temperature-resolved static mechanical data for proton-irradiated beryllium remain limited. Here, we report the behavior of PF-60 and S-65F, two widely used beryllium grades, using quasi-static uniaxial tensile and four-point bend testing at room temperature and elevated temperatures up to 400 °C. The materials were irradiated with 168 MeV protons at the Brookhaven Linac Isotope Producer (BLIP) facility to simulate service conditions relevant to high-energy accelerator environments. Mechanical properties including yield strength, ultimate tensile strength, elongation, and flexural response were evaluated to quantify the effects of irradiation and test temperature. Tensile results show pronounced irradiation hardening and embrittlement in both grades, with substantial reductions in elongation and ductility. Four-point bending complements tension by revealing temperature-dependent transitions from micro-crack initiation to macro-fracture and by providing flexural strength under a constant-moment stress field, thereby exposing failure features not evident from tensile data alone. Fractography of fractured tensile specimens correlates the observed property changes with irradiation-induced changes in fracture morphology. In parallel, ultrasonic measurements on a dose-graded specimen were used to assess the sensitivity of elastic modulus to radiation dose. Together, these results provide a temperature-resolved, application-relevant property dataset for irradiated beryllium and directly relate fracture morphology to mechanical behavior, supporting beam-window material selection and qualification under high-energy proton exposure.

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