Autoradiographic observations on the behavior of gas atoms in neutron irradiated aluminum-lithium alloys

The behavior of radiation-produced gas atoms in Al-Li alloys was observed by means of 3H autoradiography. The technique is extremely useful for studying the behavior of gas atoms in specimens containing 3H in concentrations of the order of 10−5 in atom fraction. Cold-worked microstructures of the specimen are also revealed in the autoradiographs. However, the effect of β-phase on the behavior cannot be observed by autoradiography. Precipitation of the gas atoms could not be discerned within the grain in specimens irradiated in JRR-2 at ambient-water temperature. Upon heating to 200°C, 3H was seen to precipitate along the dislocation within the grain and denuded zones free of the precipitate appeared along the grain boundaries. The amount of 3H remaining in the specimen decreases with rising heating temperature. In the case when the concentration of radiation-produced gas atoms contained is the order of 10−5 in atom fraction, gas bubbles are observed in auto-radiographs of specimens heated at a temperature as high as 500°C. On the other hand, bubbles are hardly observed in specimens heated at the same temperature when gas atoms are contained in concentrations of the order of 10−4. Cold-working after irradiation accelerates the migration of gas atoms and the growth of gas bubbles.