X-Ray Characterization of Defects in Irradiated Iron
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X-RAY CHARACTERIZATION OF DEFECTS IN IRRADIATED IRON J. PEISL, H. FRANZ, A. SCHMALZBAUER AND G. WALLNER Sektion Physik der Ludwig-Maximilians-Universittit, Geschwister-Scholl-Platz 1, 8000 Miunchen 22, FRG
ABSTRACT We report on a thorough X-ray study of irradiation induced defects in iron. Single crystals were irradiated at 4.6 K with reactor neutrons and at 90 K with 2 MeV electrons. After irradiation and subsequent thermal annealing, we measured the defect induced diffuse scattering of X-rays (Huang scattering) and the small angle scattering of synchrotron radiation. Simultaneously, lattice parameter and electrical resistivity changes were measured. The single defect properties are determined from low dose electron irradiated samples and yield the lattice distortions, i.e., the volume change and defect symmetry as described by the force dipole tensor. Excellent agreement of the experimental results with calculated values from literature is observed. After neutron irradiation, defects are correlated within displacement cascades. The correlations for vacancies and interstitials are described by a spatial correlation volume. These results are compared with computer simulations using the Marlowe code. During thermal annealing the irradiation induced defects agglomerate at characteristic temperatures and we observe changes in the spatial correlations of the defects. There is a clear difference between electron and neutron irradiated samples concerning defect recovery in stage 1.
1. INTRODUCTION Sofar research on irradiation damage has concentrated mostly on fcc metals, where the mechanism of defect production and the properties of the defects are well understood. The situation for bcc metals is different; especially iron is less thoroughly investigated. This is mainly due to the lack of well defined samples in the past. Recently, high purity Fe single crystals have become available and are investigated [1]. Diffuse x-ray scattering has been established as a method yielding information on the strength, symmetry and correlations of defects. Diffuse scattering between Bragg-reflections (Quang diffuse scattering) is mostly sensitive to lattice distortions, whereas small angle scattering is caused by fluctuations in the scattering length. HDS has been used successfully for defect studies, whereas SAS has been applied in a few cases only. The availability of powerful x-ray sources (synchrotron radiation) will make SAS a similar powerful method for defect studies. We report in the following on a study of irradiation induced defects in high purity Fe by x-ray HDS and SAS. Defects were created during irradiations by electrons and neutrons, respectively. In order Mat. Res. Soc. Symp. Proc. Vol. 209. 01991 Materials Research Society
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to study the damage in the "as-irradiated-state', irradiations were performed at low temperatures, well below the first annealing stage. In section 2 we shortly summarize the theoretical background of the diffuse x-ray scattering by defects. Experimental details are described in section 3 an
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