Characterization of 3 MeV H+ irradiation induced defects in nuclear grade graphite

Atomistic structure change in a nuclear grade graphite irradiated at 353 K to 3.4×1017 ion/cm2 with 3 MeV H+ was characterized by measuring positron lifetime and Raman spectrum at room temperature. It is evident from the positron lifetime results that the pre-existing structural defect is disoriented crystalline boundaries, and vacancy clusters ranging from di- to quadruple-vacancies were newly formed after ion irradiation. The relative intensity ratio of the Raman D and G peaks increased from 0.25 to 0.67 after ion irradiation. The concentration of radiation-induced vacancies was reasonably estimated by the Raman intensity ratio.