Damage of swift ions in crystalline calcium fluoride. Evolution of the ion explosion spike into a thermal spike

The molecular dynamics simulation of the damage caused in calcium fluoride by the passage of a swift ion energetic enough to create vacant K-states in the host during passage in the [1 1 1] direction shows that the ion explosion characterised by a collective inward motion of anions, with an outward motion of cations which initially develops in close-packed 〈1 1 0〉 directions, is overcome by a chaotic process initiated by similar ionic motions in 〈1 1 2〉 directions. This ion explosion spike degenerates in <65 fs into a thermal spike some 55 Å in diameter. Annealing is a lengthy process but by 20 ps it had become plain that the thermal spike cools to give a stable, glassy structure some 46 Å across based on disordered fluoride-sharing CaFn clusters with a central filament composed of neutral fluorine molecules.