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When a single crystal is used in an x-ray spectrometer to display the continuous spectrum of an x-ray tube by Bragg diffraction, absorption edges characteristic of the atomic species in the crystal may be observed. The change in diffracted power across an edge is fundamentally due to a change in the atomic scattering, especially the imaginary part of the scattering, of the species whose edge it is. This produces a sharp anomaly in both the structure factor and the absorption factor of the reflection being used. The explicit effect of the absorption is a function of the perfection of the crystal face; the change in the structure factor depends uniquely on (hkl) for noncentrosymmetric crystals. Thus, the absorption edges may be used as a tool to study perfection of crystal faces and polarity of polar axes. The K edges of Ga and As seen in reflection from (111) and (1̄1̄1̄) faces of perfect and mosaic crystals of GaAs are discussed both theoretically and experimentally in some detail. The linear absorption coefficient of GaAs and Ge have been measured in the course of the work.

According to this interpretation, the following are anticipated: (a) Setting the Bragg condition for the near-perfect part with Ka2 radiation, the anomalous beam produced by K~I radiation must be observed on the small-angle side of the topograph; (b) The phenomenon is purely a geometrical one and the radiation and reflexion planes used are not essential. These anticipations could be verified by taking two section topographs at the same plate position, in which Mo Kal and Mo K0c2 radiations satisfy the Bragg condition for the nearly perfect part, respectively. The result is shown in Fig. 3. The out-coming beam appears on the opposite side. In addition, a weak out-coming beam can be detected around the strong out-coming beam. Following on from this, the weak beam can be interpreted to be caused by white radiations.When such an anomalous beam appears, one can conclude that the lattice inclination is more than 4 minutes. Also, from the shape of the out-coming image, it is possible to deduce the lattice inclination geometrically, by taking into account that the diffraction phenomena in such a heavily distorted region can be treated by a kinematical theory of diffraction.The author would like to express sincere thanks to Professor N. Kato for his encouragement. A plot of Bragg's law, and some comments on diffracted energies, is given which should aid in a quick understanding of the diffracted spectrum observed with solid state detectors.The use of solid state detectors for X-rays, with their good energy resolution for X-ray photons, tends to cause one to think in terms of the X-ray photon energy rather than its wavelength. This is because the detector is usually used with a multichannel analyzer which displays the photon energies directly as channel numbers. Although they have been used mostly for non-dispersive X-ray fluorescence photon detection and energy sorting, photons diffracted in a fixed direction from crystalline samples exposed to the continuum are also easily detected and sorted with these systems. Thus 'energy powder patterns' will probably also become a standard technique (Giessen & Gordon, 1968). Revisiting Bragg's Law in terms of the energy variable leads to a very concise and symmetric expression which displays the relationship between the basic quantities very clearly.From and we get E= hv = he/2;t = 2d sin 0That is, the product of the photon energy and the d spacing and sine of one-half the scattering angle is a universal constant. For any kind of particle, the product of momentum, d spacing, and sin0, is a constant, but for photons, since energy is momentum times c, the energy expression is particularly satisfying. Numerically, if E is in kilo electron volts, d in/~ngstr6ms, and for the scattering angle 20, we have: Ed sin (20/2)= 6.195 (keV) (A).Equation (2) defines a hyperbolic surface in the three variables. In terms of a two-dimensional plot, sine of one-half the scattering angle versus E gives a family of hyperbolae, each curve representing a different value of a d spacing.A plot based on equ...

In the Borrmann effect, or the anomalous transmission, by diffraction, of x rays through perfect crystals, one state of polarization of the x-ray beam is preferentially absorbed. Since this happens in the "transmitted" as well as in the diffracted beam, a simple polarizer-monochromator is possible in the sense that insertion and rotation of the polarizer does not sensibly change the line of action of the x-ray beam. We have used as our "Borrmann crystal" a single-crystal slab of dislocation-free germanium approximately 30 mils thick and cut for symmetric Laue diffraction from the 220 planes. The details of the rotating crystal holder, an analysis of the polarization, comments on the double-crystal geometrical effects, and an example of the use of the polarizer-monochromator to study the polarization term in Bragg diffraction are presented.