RESPONSE OF HELIUM BUBBLES IN GOLD TO DISPLACEMENT-CASCADE DAMAGE

Evolution of He bubbles in Au has been followed with in situ electron microscopy during 400 keV Ar ion irradiation at 500 K. He bubbles were produced by implantation at 500 K of 3 keV He ions into prethinned Au samples that were then annealed to 670 K. During Ar irradiation, bubb les undergo athermal migration, coalescence, and disintegration. The b ubbles after annealing were underpressurized, bur Ar irradiation broug ht the bubbles to equilibrium pressure after a dose of 0.6 displacemen ts per atom (dpa). Bubble behavior can be understood on the basis of t heir interactions with adjacent cascades. We propose that a discrete b ubble jump is induced by the melt zone formed during the thermal spike phase of a contiguous cascade. The rate of bubble migration is modele d with the assumption that the jump distance is determined by the bubb le and cascade volumes.