In all cases, the curve passes through the central spot formed by the transmitted beam. When 0 = 45°, the curve becomes a parabola when 0 exceeds 45°, a hyperbola and when 0 = 90°, a straight line. For somewhat larger values of 0, the ellipse is incomplete because of the finite size of the film. When the film is in the transmission position, this curve is a complete ellipse for sufficiently small values of 0, the angle between the zone axis and the transmitted beam (Fig. In either Laue method, the diffraction spots on the film, due to the planes of a single zone in the crystal, always lie on a curve which is some kind of conic section. Pole 1 is the pole of the plane causing diffraction spot 1. 8-11 Use of a stereographic ruler to plot the pole of a reflecting plane on a stereo-graphic projection in the back-reflection Laue method. 5 = source, C = crystal, F = focal point.įig. 5-10 Focusing of diffracted beam in the transmission Laue method. In the back-reflection Laue method the film is placed between the crystal and the x-ray source, the incident beam passing through a hole in the film, and the beams diffracted in a backward direction are recorded. This method is so called because the diffracted beams are partially transmitted through the crystal. The film in the transmission Laue method (the original Laue method) is placed behind the crystal so as to record the beams diffracted in the forward direction. In each, the film is flat and placed perpendicular to the incident beam. There are two variations of the Laue method, depending on the relative positions of source, crystal, and film (Fig. Each diffracted beam thus has a different wavelength. The Bragg angle 6 is therefore fixed for every set of planes in the crystal, and each set picks out and diffracts that particular wavelength which satisfies the Bragg law for the particular values of d and 9 involved. A beam of white radiation, the continuous spectrum from an x-ray tube, is allowed to fall on a fixed single crystal. The Laue method was the first diffraction method ever used, and it reproduces von Laue s original experiment. In place of Bragg s law, dhk) = X/2 sin 0hk), the TOF relationship is. The diffraction experiment uses the Laue method and the wavelengths are measured by their time of flight (TOF). Since the electron beam is pulsed, so is the neutron beam.
The other source is the continuous wavelength spectrum of neutrons produced by stopping an accelerated beam of electrons, i.e., the spallation source. įIGURE 2.2 X-ray diffraction by a crystal of beryl using tbe Laue method. Macromolecule single-crystal structure determination, 26 426-427 Macromolecule structure, interactions related to, 13 742-743 Macromolecule X-ray diffraction, Laue method for, 26 442. Laudanosine, 2 87, 89 Laue method, for macromolecule X-ray diffraction, 26 442 Laundering. , and a formal second order perturbation theory has been developed by Peng. A formal mathematical expression for the first order partial derivatives of the scattering matrix has been derived by Speer et al.
Applications have been made to take into account the effects of weak beams inelastic scattering higher-order Laue zone diffraction crystal structure determination and crystal structure factors refinement. In the context of electron diffraction theory, the perturbation method has been extensively used and developed. For simplicity, in this section we will be concerned with only periodic structures and a transmission diffraction geometry. In this section we will discuss perturbation methods suitable for high-energy electron diffraction. This technique caimot be used with conventional x-ray sources. By collecting many complete data sets over a short period of time, the Laue method can be used to foUow the reaction of an enzyme with its substrate. In this case, all of the reflections that ate diffracted on to an area detector are recorded at just one setting of the detector and the crystal. Instead of using monochromated x-rays, a wide spectmm of incident x-rays is used. A new technique, the Laue method, can be used to collect all of the data in a fraction of a second. As indicated above it is possible to determine the stmctures of macromolecules from x-ray diffraction however, it normally takes a relatively long period of data collection time (even at synchrotrons) to collect all of the data. Laue method, diffraction Laue Method for Macromolecule X-Ray Diffraction.
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