. Adventures in radioisotope research;. Radioactive tracers; Radiobiology. DIFFUSION IX METALS 123 stoadily decreasing diffusion velocity. The margin l)etween the diffusion velocity of the added element and that of lead thus becomes steadily smaller and the unilateral fliffusion becomes gradually less apparent. Considering now an alloy of ordinary and radioactive lead, both con- stituents will exhibit the same diffusion velocity. This is an example of self-diffusion and therefore a complete mutual replaceability in the 220 2^0 260 2S0 300 320. Fig. 1. Diffusion in Blcilogieiungen — Diffusion i
. Adventures in radioisotope research;. Radioactive tracers; Radiobiology. DIFFUSION IX METALS 123 stoadily decreasing diffusion velocity. The margin l)etween the diffusion velocity of the added element and that of lead thus becomes steadily smaller and the unilateral fliffusion becomes gradually less apparent. Considering now an alloy of ordinary and radioactive lead, both con- stituents will exhibit the same diffusion velocity. This is an example of self-diffusion and therefore a complete mutual replaceability in the 220 2^0 260 2S0 300 320. Fig. 1. Diffusion in Blcilogieiungen — Diffusion in lead allo,>s Schmclzpunkt des Blcis — Melting point of lead diffusion process. The gradual decrease of diffusion velocities of metals in lead in the sequence, Au —Pb, Pb —Pb, and also the step-wise increase of the heat of relaxation (heat of activation), can be seen in Fig. 1. The latter quantity is also recorded in Table 1. The marked preferential diffusion of one component is also encountered in salt-like compounds but there is no mutual replaceability of the components which, indeed, is a characteristic of metallic systems. The silver in silver chloride can only change places with silver; it is other- wise in metallic alloys. Considering the place-exchange processes in a saturated silver-lead phase, the readily detachable silver atom will leave its place with great frequency in unit time. The silver atoms intermit- tently seek out the lead atoms and occasionally also replace other silver. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hevesy, Georg von, 1885-1966. New York, Pergamon Press
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