The different influences of the general grain boundary and the twin boundary on the cavity formation were investigated in copper irradiated by helium at room temperature. Large number of the cavities with sizes smaller than 5 nm formed after irradiation, which were almost homogenously distributed inside the grains. However, the distribution of the cavities varied near the general grain boundary and the twin boundary. Cavities-depleted zone was readily observed near the general grain boundaries, which was rarely observed near the twin boundaries. Meanwhile, decoration of dense cavities within the grain boundary plane was observed. The results suggested the limited influence of the twin boundaries as the point defect sinks compared with the general grain boundaries.
