The effects of irradiation temperature and preinjected gases on voids in aluminum

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Abstract
Voids in high purity aluminum irradiated to a fast (E>1 MeV) fluence of 4 × 1020 n/cm2 at 125 (0.43T m) and 150°C (0.45T m) are fewer in number but very much larger in size than those in material irradiated at 55°C (0.35T m). Additionally, at 125 and 150°C, the voids adopt a variety of shapes including plates, ribbons, cylinders and more equiaxed polyhedra, and are frequently associated with particles of transmutation-produced silicon. At the higher temperatures voids are larger near grain boundaries than in grain interiors. Injection of hydrogen or helium prior to irradiation causes an increase in the number of voids and a corresponding decrease in size in specimens irradiated at 150°C; 3 at. ppm He is more effective than either 3 or 9 at. ppm H. The gases do not appear to influence swelling. A commercial purity (99 per cent) aluminum subjected to the same irradiation treatments did not develop voids whether preinjected with gases or not; the visible radiation damage consisted solely of small loops on or near grown-in dislocations.