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Single crystals of a-iron were irradiated perpendicularly to the (100), (110), and (111)planes with electrons in the range 0.35 -1.7 MeV and their electrical resistivity change rates were measured. A geometrical model of the threshold-energy surface for atomic displacement in a bcc lattice produces a fit to the experimental data leading to the following values for the threshold energies in the principal crystal directions: Tz ' --17 + 1 eV, T""'~= 20+ 1.5 eV, and T""~30 eV. The specific resistivity of a Frenkel pair is deduced to pF"' --(30~5) p.Qcm/at. %%uo . From th eobtaine dT"'sw ederive da n interatomi cpotentia 1 of th eBorn-Maye r typ e, vali d in the range 1.2 & r & 2.5 A. We propose as a good choice: V(r) = 8900e "" eV. The recovery due to isochronal annealing during stage I, after irradiation at different electron energies, was measured and related to specific recovery mechanisms. Thus, the first important substage, I~(-66 K), is due to the recovery of close Frenkel pairs created in the (100) direction, while a comparison of calculated cross sections suggests that Ic (-87 K) possibly stems from (111)close pairs. Substage ID (90 -110 K) is complex; its first part, below 100 K, originates mostly from defects produced in the (100) direction and the second part, above 100 K, together with IE, principally originates from defects produced in the (111)direction.

For pt.I see ibid., vol.2 no.47, p.9269-90, 1990. Three series of dilute iron alloys, FeNi, FeMn and FeCu, with concentrations ranging from 50 at.ppm to 3 at.%, have been electron-irradiated at low temperature and annealed up to room temperature. The recovery spectra of the radiation-induced resistivity show that mixed-interstitial migration takes place, in the FeNi alloys, at the beginning of stage II (130-150 K, depending on the Ni concentration), thus providing evidence of the formation of stable mixed-interstitial Fe-Ni during self-interstitial migration in stage I. Mixed interstitials are deduced to be formed also in FeMn and FeCu alloys although they are not stable above stage I and are not directly observable. Mixed poly-interstitials migrate below stage III (i.e. below 200 K) in the three alloys studied. Such a migration instead of break-up results in the growth of larger mixed-interstitial clusters and leads to solute clustering and correlated solute bulk depletion. Bulk depletion was indeed observable in the FeCu and, to a lesser extent, in the FeNi dilute alloys through a diminution of the residual resistivity of the samples. In the FeMn concentrated alloys (1 and 3%), the mixed poly-interstitial clustering gives rise in stage II to gamma -precipitation which largely survives the vacancy migration.