The direct observation of radiation damage in platinum

Thin foils of platinum were examined by means of transmission electron microscopy. Annealed foils show features typical for a face-centered cubic metal with a medium high stacking fault energy. Prismatic loops with an a/2 |110] Burgers vector result from irradiation; this could be shown by observing their motion. The loops anneal out at about 500° C. Preferential loop formation is noticed at certain boundaries, in particular along coherent twin boundaries. This is considered as evidence for correlated collision chains leading to preferential defect formation at these boundaries. For small doses, dislocation loops are not distributed at random in the interior of the grains but show a tendency to align. This is interpreted as resulting from loop nucleation along the path of a fission fragment. The damage rate of quenched specimens seems to be larger than that of annealed ones; the loop concentration is less along a zone parallel to boundaries and subboundaries. It is suggested that either the vacancy clusters left by quenching are nucleation sites for loops, or that the vacancy clusters defocus collision chains and hence increase the damage. It is shown that as well vacancy as interstitial loops are left after fission-fragment and partiele irradiation at liquid-nitrogen temperature. The loop character was determined
by means of contrast effects. It is concluded that geometrical factors are important in determining the distribution of damage and that loop nucleation is heterogeneous and rate-dependent.