The observation of vacancy sources in metals

Abstract

Abstract Helium atoms have been injected into copper by alpha-particle bombardment in a cyclotron. On subsequent heating, the helium precipitates out as small gas bubbles in those parts of the metal where the helium atoms receive vacancies from nearby sources. From the distribution of the gas bubbles it is concluded that grain boundaries are effective sources of vacancies, but twin boundaries are not. Isolated sources of vacancies exist within the crystals, but there is no evidence that the dislocation network generates appreciable numbers of vacancies.