New aspect of diffraction of a highly divergent characteristic X-ray beam
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RACTION AND SCATTERING OF IONIZING RADIATIONS
New Aspect of Diffraction of a Highly Divergent Characteristic XRay Beam K. T. Avetyan Yerevan State University, Yerevan, 0025 Armenia email:[email protected] Received September 10, 2009
Abstract—A new way of implementing the diffraction of a highly divergent characteristic Xray beam has been developed. This method is based on the formation of a diffraction image by the X rays exiting particular (active) points on the crystal surface which lie on hyperbolas. There is a correspondence between the points on the crystal surface and the points in the diffraction image. Local distortions of the crystal structure lead to local deviations of the diffraction lines from proper hyperbolas. This method makes it possible to reveal the block structure of crystals, separate blocks, and estimate the degree of misorientation. DOI: 10.1134/S1063774510050032
INTRODUCTION When a highly divergent beam (HDB) of charac teristic X rays undergoes diffraction, the diffraction condition is simultaneously satisfied for several sets of atomic planes (sometimes as many as 20 or even 30). The HDB diffraction image contains rich and peculiar information about the structural features of crystals. Kossel was the first to implement HDB diffraction using a copper single crystal as an Xray tube anode. Furthermore, the HDB diffraction has repeatedly been a subject of study in view of the more severe requirements for the analysis of new crystalline mate rials and the development of an experimental tech nique. In some studies capillary timeofflight Xray tubes with a focal spot several micrometers in size were used as point characteristic Xray sources [1–3]. In [4, 5], characteristic X rays were excited by a focused electron beam and collimated synchrotron radiation (with spots 10 and 100 μm in diameter, respectively). A new technique was developed in [6, 7], where the variety of grazing angles caused by the beam divergence is replaced by a continuous change (in necessary limits) in the crystal orientation (along with the photographic plate) with respect to the beam. The measurement technique and the residual stress data, which were obtained by combining different techniques [6–9], were reported in [8, 9]. Some units of a scanning electron microscope were used to obtain a characteristic Xray beam with a small focal spot [10, 11]. A method for implementing HDB diffraction based on the standard equipment (DRON2 and DRON3 diffractometers) was developed in [12, 13]. In this technique, X rays passed through a diaphragm mounted near the output window of the Xray tube.
The crystal under study was placed near the diaphragm (before or after it), and the photographic plate was ori ented parallel to the diaphragm plane. In this study we developed a new version of charac teristic Xray HDB diffraction and demonstrated its potential for studying the block structure of crystals. GEOMETRIC FEATURES AND SCHEMATIC OF THE EXPERIMENT In the new version, a crystal under study (thin plate with µ t < 1) is place
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