Study of radiation damage in aluminum

Abstract

A mathematical model to describe the radiation damage in aluminum is presented. The concentrations of monointerstitials, di-interstitials, interstitial clusters, monovacancies, divacancies, and vacancy clusters, and the average sizes of the clusters are calculated and plotted as a function of the irradiation dose at liquid-helium temperature and the thermal annealing temperature. Any irradiation dose (electron, neutron, heavy ion) is expressed as the number of interstitials or vacancies per atom which has been produced (cipa for created interstitials per atom). Also calculated are the fractions of Co impurities, present in the aluminum, which have trapped one or more interstitials or vacancies. With the use of M\"ossbauer spectroscopy these fractions are measured experimentally as a function of the dose of a heavy-ion implantation and of the annealing temperature. The unknown parameters in the model, which are mainly trapping volumes, are determined by fitting the calculated values to the experimental data. The model calculations, executed for a large range of irradiation doeses and annealing temperatures, reproduce nicely our experimental results as well as results reported by other groups. The calculations indicate that an irradiation dose of 0.001 cipa yields a concentration of interstitials (and vacancies) of almost 0.0007, mainly present as monointerstitials and monovacancies; at 0.01 cipa it is about 0.002, distributed over the various defect configurations; at 0.1 cipa it is about 0.003 with nearly all interstitials in clusters with an average size of about 15 and vacancies still mainly present as monovacancies. The trapping volumes for interstitials are larger than the corresponding ones for vacancies and therefore interstitials cluster more easily than vacancies. Of the Al atoms displaced during the collision cascade produced by one 85-keV Al atom, about 20% is removed outside the volume for recombination with its own vacancy.