Hall effect measurements of frenkel defect clustering in aluminium during high-dose reactor irradiation at 4.6 K

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Abstract
The low-field Hall coefficient R0 of irradiated aluminium at 4.6 K is independent of the Frenkel defect (FD) concentration, however sensitively dependent of their configuration. Since measurement of R0 is not too difficult, rather extensive investigations of FD clustering during irradiation can be performed, but only qualitative interpretations are possible. We have irradiated several pure Al samples with reactor neutrons at 4.6 K up to very high doses φt resp. resistivity increments Δρ0 (maximum 91% of extrapolated saturation value Δρ0 sat ≈ 980 nΩcm). Our main results are: 1. FD clustering within a single displacement cascade is not a very strong effect in Al, since the R 0 values are essentially the same after reactor and after electron irradiation. Rough cascade averages are: volume Vc ≈ 2.1 · 105 at. vol. and FD concentration cc ≈ 1100 ppm. 2. There is practically no dose-dependent FD clustering up to Δρ0 ≈ 350 nΩcm, since R 0 remains essentially constant there. It follows that dose-dependent FD clustering can only occur for high-order overlap of cascade volumes. The differential dose curve dΔρ0/dφt is perfectly linear in Δρ0 as long as R0 = const. 3. For Δρ0 > 350 nΩcm FD clustering becomes increasingly important and R 0 changes strongly. Surprisingly dR 0/dφt ≈ const whence there is a constant rate of cluster size increase in spite of the vanishing rate of FD production, evidence of the continuous regrouping of the lattice and its defects.