Microstructure evolution of beryllium during proton irradiation

The effects of proton irradiation on a beryllium reflector in terms of microstructure evolution have been studied to emulate the effects of neutron irradiation. Protons were irradiated on a beryllium sample with the acceleration voltage of 120 keV and the fluence of 2.0 × 1018 ions/cm2 at room temperature. The size of the irradiation damaged layer was estimated through a Monte Carlo simulation (SRIM2012 software) and transmission electron microscopy (TEM) observation. While the irradiated sample was observed by using TEM, the size of the damaged layer was roughly 1 µm, and the value was coincident with the simulation result. The most severely damaged area was occurred at 600 nm in depth; tens-of-nanometer-sized voids were distributed. Multiple voids were observed in the entire damaged area, and were preferentially distributed along the grain boundaries, and the interfaces between the matrix and the BeO particles. Equi-axed voids, 10 nm in diameter, were observed in the grain boundary, and planar voids were observed at the interfaces. The voids were also distributed in the grains; the evolutions of the voids were observed to have been affected by the grain orientation rather than the irradiation direction. The selective area diffraction pattern (SADP) from TEM showed that the arrays of multiple voids were considerably longer along the basal plane. The beryllium atoms could be easily dislocated by proton irradiation while the basal plane was aligned along a direction perpendicular to the irradiation.