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The effect of substructural perfection on the accumulation of irradiation damage in aluminum was examined. Large single crystals with extensive substructure and crystals essentially free of substructure, all with faces cut parallel to crystal planes, were subjected to neutron irradiation. Subsequent examination by X-ray diffraction revealed pronounced changes in integrated intensity and Debye-Waller temperature factor for the substructure-free crystals; these effects disappeared upon re-etching of the surface. Laue photographs showed that the normal single-crystal pattern was partially obscured by a polycrystalline effect which also disappeared upon etching. Crystals with extensive substructure showed no such effects.
This diffraction evidence supports the view that irradiation-induced defects in aluminum migrate to and collect at the crystal surface if no internal trapping sites exist.