2, Texas A&M University, College Station, Texas, United States
The buildup of radiation damage in nuclear materials often depends on the spatial distribution of atomic displacements within collision cascades. Although collision cascades have previously been described as fractals, the correlation of their fractal parameters with experimental observations of radiation damage buildup remains elusive. Here, we use a recently developed pulsed-ion-beam method to study defect interaction dynamics in SiC irradiated at 100 C with 500 keV ions of different masses. Experimental data is analyzed with a model of radiation damage formation which accounts for the fractal nature of collision cascades. Our emphasis is on the extraction of the effective defect diffusion length from pulsed beam measurements. Results show that collision cascades are mass fractals with fractal dimensions in the range of ~1-2, depending on ion mass, energy, and the depth from the sample surface. Within our fractal model, the effective defect diffusion length is ~10 nm, and it decreases with increasing cascade density. These results demonstrate a general method by which the fractal nature of collision cascades can be used to explain experimental observations and predict material's response to radiation. This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.