1.1- Camera or diffractometer ?

- Cameras (Debye, Gandolfi, Guinier) have a low cost advantage. Because of the need to impressed a photographic film and to develop it, cameras cannot rival with diffractometers on the speed point of view for a routine identification. However, structure refinements and even full structure determinations have been realized from data provided by powder cameras. One should emphasized that Guinier cameras offer one of the highest resolution attainable by a laboratory instrument with FWHM (Full Width at Half Maximum) as low as 0.06° or 0.08° (2-theta) for the minimum. Cameras may come back 'à la mode' if some multidetectors and bidimensional detectors make progresses and replace film/densitometers. Such progresses are expected because they are necessary for using fully the fantastic possibilities offered by synchrotron radiations, conventional X-ray sources will benefit of them.

- Commercial diffractometers are dominated by the Bragg-Brentano geometry up to 90%, the other 10% are Seeman-Bohlin diffractometers. The present scenario considers a Bragg-Brentano mounting, with a fine focus anode, a diffracted-beam monochromator (eliminating Kß and a large part of fluorescency problems, but not removing Kalpha-2), a scintillation counter, Soller slits before and after the sample, allowing to measure on horizontal samples (which will fall down near 130° 2-theta if not compacted, anyway). Current performances of the Bragg-Brentano diffractometers allow minimal FWHM as low as 0.04° (2-theta) by using variable slits.


Copyright © 1997- Armel Le Bail