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 x 10(17) ion/cm(2) with 3 MeVH+ 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. (C) 2010 Elsevier Ltd. All rights reserved.