Valuable information on the interatomic forces and energies in solids can be drawn from scattering experiments on crystals containing randomly distributed defects. However, defect concentrations usually have to be kept small to ensure random distribution and this is one of the reasons for a generally low signal. Neutrons can be used with advantage for such investigations if the incoherent‐scattering cross section of the host material is small. The particular properties of slow neutrons make it possible to apply a number of experimental methods to obtain the desired information. Variation of incident energy and resolution in momentum space, the use of different isotopes as defects and – in particular if the experiments have to be done at high temperatures – analysis of the energy of the scattered neutrons may help to compensate for the usually low luminosity of neutron sources as compared, e.g., to X‐ray tubes. Careful design of the sample's environment and appropriate choice of experimental parameters allow measurements on samples with defect concentrations down to 0.1 at. % and at temperatures up to several hundred Centigrade. Experimental facilities of this type have been installed in Jülich and in Grenoble. The results obtained so far on various alloy systems show that considerable success is possible.
The diffuse elastic neutron scattering caused by the distortion of the Pb-host lattice around the Bi substitutional atoms has been investigated. In the long wavelength limit the scattering agrees with the value calculated from the lattice parameter change. Along the [I001 direction the shape of the scattering can be explained by equal nearest neighbour radial outward forces due to the defect. An intensity peak around the 110-reciprocal lattice point, however, requires the assumption of an additional non centrosymmetric force.A model for such a force is discussed. Es wurde die durch das Verzerrungsfeld von substitutionellem Wismut in Blei hervorgerufene Verinderung der diffusen elastischen Neutronenstreuung untersucht. Fur kleine Wellenzahlen ergibt sich eine Streuung wie sie aus der Gitterparameteranderung berechnet werden kann. Fur die Streuung parallel zur [loo]-Richtung konnen die Messungen befriedigend mit radialen, nach auBen gerichteten, nur auf nichste Nachbarn wirkenden Zusatzkriiften gleicher GroBe erklirt werden. Fur die Berechnung eines Maximums der Streuintensitiit a m 110-Punkt des reziproken Gitters ist jedoch eine zusiitzliche, nicht zentralsymmetrische Zusatzkraft erforderlich. Ein Model1 mit einer solchen Kraft wird diskutiert.
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