EXPERIMENTAL PROCEDURE

High density n-Fe specimens were prepared by compaction of inert-gas condensed nanocrystallites. The compaction at 403 K with a pressure of 3.1 GPa in a UHV system at a vacuum of 10^-8 mbar yielded high-density n-Fe disks with a diameter of 8 mm and a thickness of 0.15 mm. The variation of the relative density (p/p_c p_c : bulk Fe density) with the mean grain size (d) of n-Fe disks, where p and d were determined by the Archimedes technique and from the broadening of x-ray diffraction peaks, respectively. The preparation of n-Fe specimens with lower p but smaller d was previously reported by compaction of gas condensed nanocrystallites at 373-571 K with pressure of 1.4 GPa in vacuum of lo-’ mbar (4). For the present diffusion studies, n-Fe specimens with p/p_c, of 91 - 96 % and d of 19 – 38 run were used. It is noted that no obvious change in the diffusion behavior was found in these p and d ranges. The “Fe radiotracer was deposited on the polished specimens by thermal evaporation and afterwards the specimens were annealed (diffusion annealing) in an evacuated glass vial. After sputter sectioning by Ar-ions, the radioactivity of the sputtered sections was counted in order to obtain the penetration depth profile of 59Fe tracers (5).