Anomaly in dependence of radiation-induced vacancy accumulation on grain size

According to conventional steady-state rate theory predictions of displacement damage evolution in irradiated materials, the accumulation of vacancies decreases as grain size decreases. Using atomistic simulations, the authors report a transient anomaly in the dependence of radiation produced vacancy accumulation on grain size. Contrary to the conventional wisdom, the accumulation of vacancies can be higher in smaller grains than in larger grains during a transient stage. The anomaly is a result of competition between two atomic-level processes: grain boundary absorption and bulk recombination of point defects, each of which has characteristic length and time scales. Copper is used as the prototype of face-centered-cubic material and Frenkel pair production mimicking electron radiation is the source of non-cascade defect introduction, both choices aiming at clarity for identifying physical mechanisms.