RADIATION-ENHANCED DIFFUSION OF ~(63)NI IN NICKEL AND IN COPPER

摘要

Radiation-enhanced diffusion coefficients of ~(63)Ni in nickel and in copper were determined between -100°C and +500°C after an irradiation with 1.85 MeV electrons which were obtained from a Van de Graaff generator. The diffusion coefficients were obtained by counting the activity of successive layers from the surface of single crystals which were removed by means of sputtering. The dislocation density of the crystals was smaller than d = 10~(-4) cm~(-2) and the evenness of the surfaces of the crystals was better than 20 A. It was found that the radiation-enhanced diffusion coefficients were approximately independent of the irradiation temperature in the "low" temperature regime, i.e. below about 100°C, and about 1.3·10~(-20) cm~2·s~(-1) and 1.1·10~(-20) cm~2·s~(-1) for nickel and copper, respectively. The replacement collision sequence number of dynamic crowdions was derived from these results and values of N ≈ 50000 and N ≈ 40000 were obtained for nickel and copper, respectively. The same values were obtained previously from measurements of the radiation damage rate. The radiation-enhanced diffusion coefficients were obtained for "high" irradiation temperatures, dependent on the irradiation temperature, and were approximately in agreement with those obtained by computation assuming that the migration activation energy of interstitials was E_(IT)~M = 0.869 eV and E_(IT)~M = 0.584 eV for nickel and copper, respectively (for K = 6.3·10~(-10) dpa·s~(-1)) . Dynamic crowdions can dissolve e.g. precipitates, and three-dimensionally migrating point defects can usually form precipitates.