Diffusion coefficients for the diffusion of zinc in 10% Zn — 90% Cu single crystals are determined for both irradiated samples and unirradiated samples. This is accomplished by measuring the zinc lost from the samples when they are heated in a vacuum of 3×10−5mm Hg at temperatures from 207°C to 316°C. The zinc loss is measured by observing the change in optical reflection coefficient at a wavelength of 550 m&mgr;. The diffusion length (Dt)½is then found using the known optical constants of ZnCu alloys and the expected concentration distribution. The diffusion lengths thus obtained range from 20 to 1000 A. Bombardment by a 30‐kev Ne+ion beam of 2.9 &mgr;a/cm2produces defects at a calculated rate of 4.5×10−2atomic fractions/sec over the depth of 300 A penetrated by the beam. For well‐annealed samples the bombardment enhances the diffusion. The radiation‐enhanced diffusion coefficient depends on the square root of the bombarding flux density and has an activation energy of 9300±1700 cal/g mole. The results agree with theoretical predictions for enhanced bulk diffusion for the case of defects annealing by direct recombination plus linear anneal to fixed sinks.