Large swelling and percolation in irradiated zircon

We study the effect of large swelling in irradiated zircon. We perform molecular dynamics simulation of the overlap-of two radiation events and find that the damage produced in the second event scatters away from the densified boundary of the damaged region implanted previously. This serves as the microscopic,mechanism of the increase of volume occupied by the damage. The additive nature. of this effect results in large swelling observed experimentally. We translate the damage accumulation into the percolation problem, and show that volume swelling is a percolation phenomenon, with the swelling curve increasing rapidly at the percolation threshold.