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A large disk-shaped specimen of nanocrystalline metal copper, with a diameter of 80 mm and thickness 5 mm, was synthesized by an inert gas condensation and insitu warm compacting technique. The grain size and density of the specimen are 36 nm and 94.3 % of standard density, respectively The positron lifetime and intensity were measured for monitoring the defects in the specimen. The results indicated that the size and amount of the vacancies and microvoids in the large specimen are close to that found in the small specimens of other nanostructured materials prepared by the same technique. The tensile stress-strain curve has been precisely measured by using the load cell and foil strain gauge. The results showed that the elastic modulus, yield stress, fracture strength, elongation and mirohardness are 0.65, 1.42, 1.82, 0.20 and 6 times of that for coarse-grained polycrystalline metal copper, respectively. (C) 1999 Acta Metallurgica Inc.