Dépouillement par ordinateur des clichés de diffraction obtenus par la méthode de Laue

The category Computer Program Abstracts provides a rapid means of communicating up-to-date information concerning both new programs or systems and significant updates to existing ones. Following normal submission, a Computer Program Abstract will be reviewed by one or two members of the IUCr Appl. Cryst. (1985). 18, t89-t90].J. AppL Cryst. (1996) (Received 7 Febrary 1996; accepted 9 April 1996) The crystallographic problem: The use of computer programs has considerably simplified the determination of unknown crystal orientation, avoiding the classical method using stereographic projection and Wulff nets. Simulations may also be useful for teaching purposes.Since the first simulation of a Laue pattern by KrahI-Urban, Butz & Preuss (1973), many programs have been written for the simulation and/or indexation of Laue diagrams. Some of them are referenced by Marin, Cintas & Di~guez (1994).Up to now, it seems that no modern general program dedicated to the processing of diffraction data has been available on UNIX workstations, except the LAUEGEN package of Campbell (1995). However, LAUEGEN is a large program, requiring a lot of disk space, involved in a suite whose aim is the computation of integrated intensities with a view to structure resolution, while LAUEX is only a small simulation/indexation program for everyday work. Method of solution:LAUEX is a userfriendly program, with an X Window graphical interface. The user enters data in the menus and chooses options by clicking on buttons or moving sliders with the mouse. The data may be saved for later use.LAUEX performs the following tasks: (i) Simulation of a Laue diagram, from knowledge of the orientation of the crystal, the cell parameters and the position © 1996 International Union of Crystallography Printed in Great Britain -all rights reserved of the detector. Note that LAUEX is not limited to the transmission and reflection cases, but that the position of the detector may be located anywhere on a sphere centred on the crystal. This feature has been introduced especially for work carried out at a synchrotron. If the structure of the crystal is known, the program may evaluate the intensities of the Laue spots and draws them as spots whose size is proportional to their intensity. The parameters taken into account for this computation are those described by Preuss (1979) (except for the crystal shape), plus the response curve of the detector.(ii) Indexation of an experimental Laue diagram, by the knowledge of the cell parameters and the position of a number of spots of low index. The indexation procedure has been suggested by Riquet & Bonnet (1979) and has already been used by Laugier & Filhol (1983).(iii) Alignment of a crystallographic direction along an axis of the apparatus (usually the one pointing towards the X-ray source), or rotation of the crystal.(iv) Storing of the simulated diagram as a PostScript file, or printing directly to a laser printer.On-line help is available if a World Wide Web (WWW) browser is installed on the machine.Software enviro...

“…The indexation procedure has been suggested by Riquet & Bonnet (1979) and has already been used by Laugier & Filhol (1983).…”

Section: Methods Of Solutionmentioning

confidence: 99%

Crystallographers

1996

“…For orientation determination the first two diffraction spots selected should be far apart to enhance the accuracy of VI (Riquet & Bonnet, 1979). Lower index limits decrease the computation time and consequently the spots should be from the intersection of zone curves (Amor6s, Beurger & Canut de Amor6s, 1975).…”

Section: Symbolmentioning

confidence: 99%

An interactive program for crystal orientation and martensitic transformation investigations:COATI

Dean¹

1985

An interactive program for comparison of experimental with theoretical martensitic transformation data and for orientation determination from Laue and zero-layer reciprocal-lattice photographs is described. The program can generate orthographic, gnomonic, Laue and zero-layer reciprocal-lattice projections of lattice vectors, circles and latitude-longitude nets. A utility for habit-plane calculation from surface trace data and its diagrammatical representation is provided. Drawings before and after transformation can be superimposed. Output from program MRTNST [Ledbetter & Wayman (1971

“…Its primary applications have involved crystal orientation and the investigation of Friedel symmetry, and the method has received only occasional attention in the literature in recent years (Ahmed & Georgeoura, 1963;Amoros, Buerger & Amoros, 1975;Riquet & Bonnet, 1979;Hart & Rietman, 1982;Lauger, 1983;Wood, Thompson & Matthewman, 1983;Fewster, 1984). With the advent of pulsed neutron sources and synchrotron Xray sources along with position-and energy-sensitive detectors, it is now the subject of renewed interest since the Laue method potentially makes better use of the available incident spectrum (Moffat, Szebenyi & Bilderback, 1984).…”

Section: Introductionmentioning

confidence: 99%

An orientation-matrix approach to Laue indexing

Jacobson¹

1986

A Laue indexing method is described which employs an orientation-matrix approach; it is especially suited for use in the case of a diffractometer equipped with a position-and energy-sensitive detector at a pulsed neutron source or synchrotron X-ray source. The crystal can be in any orientation and lattice constants need not be known. Using this method positional and wavelength information can be easily converted into a form suitable for an automatic indexing procedure in order to obtain indices and an orientation matrix, or with knowledge of the latter to predict positions of reflections incident on a detector centered at any desired 20.