The period of the last fringe was measured with 0.8 µm width. In the diffraction pattern, the accumulated dose was varied from 1.7 × 10 5 J cm -3 in the central maximum to 2 × 10 -2 J cm -3 in the 16th maximum of diffraction fringes. At the PETRA III facility, the diffraction pattern created behind a circular aperture with a diameter of 5 µm irradiated by a beam with a photon energy of 500 eV was recorded on a LiF crystal. In this work, it is demonstrated that the use of lithium fluoride (LiF) as a photoluminescence (PL) imaging detector allows measuring of an X-ray diffraction image with a dynamic range of ∼10 7 within the sub-micrometre spatial resolution. Go to Next Section or to Top of Page to Select or to Main Menu.The unique diagnostic possibilities of X-ray diffraction, small X-ray scattering and phase-contrast imaging techniques applied with high-intensity coherent X-ray synchrotron and X-ray free-electron laser radiation can only be fully realized if a sufficient dynamic range and/or spatial resolution of the detector is available. The International Centre for Diffraction Data maintains JCPDS (Joint Committee on Powder Diffraction Standards) cards for about 500,000 powder diffraction patterns (as of 2006), which can be used to identify substances in a given diffraction pattern such as shown in Figure 13-04d (CPS stands for counts of X-ray photons per second).įigure 13-04d Powder Diffraction The graph shows the intensity variation produced by the various Bragg planes. Figure 13-04b plots the intensity of the scattered waves versus twice the incident angles obtained by the diffractometer similar to the one shown in Figure 13-04a. It is not necessary to orient the crystal in various positions to obtain diffraction patterns for different Bragg planes.
Another method is to grind the specimen into powder (to the size of about 10 -4 cm) and put them in a holder. For crystal with regular spacing between atoms, the ring breaks up into spots as shown in Figure 13-04a. The diffraction pattern for a piece of amorphous material (such as glass) usually appears as concentric rings around the un-scattered beam image.Where the Miller indices (h k l) are defined as the reciprocals of the fractional intercepts (see Figure 13-04c for a graphical explanation). The spacing between the Bragg planes "d" is related to the inter-atomic distance "a" by the formula:.The angular range of the diffractometer usually restricts n to be 1. Where d is the spacing between Bragg planes, is the incident angle, is the wavelength, and the integer n is the order of the scattered beam, e.g., higher number of n corresponds to bright spot further away from the incident direction. The formula for such constructive interference is : At certain incident angles to the crystal planes (Bragg planes) the scattered beams add together constructively to form bright.The un-scattered incident waves appear as a bright spot (black in a photographic plate) at the center (Figure 13-04a). The oscillations in term re-emit radiation in all directions in the form of spherical waves.
Each dipole oscillates under the influence of the electromagnetic waves.
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