Dear Reinhard and Tony Wang,
Thank you very much for your comments. I have deeply appreciated all of them. Motorised „beam knife edge“ would be a nice thing. However, I have already asked for its price and it is really not cheap… I have made a few preliminary scans with the Variable Detector Opening mode (VDO), which seems to be useful for this purpose. However, it produces very noisy data at low angles (close to the start angle), where fewer channels are open. I will try other scans with different opening window of the detector at the beginning. Petr Bezdicka has also mentioned (in our private today´s morning talk), that reducing the detector window to e.g. 1° for whole scan can be also worth trying. Reinhard, please, could you send me in a picture of the mentioned blade (the blade itself and its position in diffractometer)? Thank you again, Frantisek Laufek From: rietveld_l-requ...@ill.fr [mailto:rietveld_l-requ...@ill.fr] On Behalf Of Reinhard Kleeberg Sent: Monday, October 24, 2016 9:00 AM To: iangie; František Laufek Cc: rietveld_l@ill.fr Subject: Re: Data collection strategy from low angles - Bruker D8 Advance, Lynx Eye XE detector Dear Frantisek, the best way to measure a clean diffraction pattern for clay mineral analysis is of course to avoid beam overflow, either by choosing a bigger sample length or a smaller fixed (or automatic) divergence slit. However, if you are using the ADS (what should make sure that you primary beam bundle hits the sample only) and you have still a "positive effect of the knife edge" on background slope at angles below 7 deg, this is simply a message that your primary beam bundle isn't "clean"! If this "knife edge" really keeps away any kind of radiation from the detector, you can simply calculate (or draw) the connection from the detector channel at this angle over the knife edge position (2.5 mm above the sample) towards the "source" of your unwanted background. The line ends about 6-8 mm below the beam center, in front of the tube window. This radiation is neither from the sample nor any "air scatter", but simply from the material region around the lower edge of the tube housing or the shutter opening. This area is hit by the intense primary bundle (before the divergence slit) and becomes a source of fluorescence/scatter. From here this radiation can pass the divergence slit inclined and above the sample, and so it reaches the detector. In fact, if there would be a second slit position close to the tube shutter (as it was constructed in older instruments), this unwanted radiation could be blocked effectively before reaching the ADS. We tried this by inserting some tungsten or steel blades glued in the filter frame of the Panalytical Empyrean instrument, and it works very well, without cutting the beam bundle at higher angles as the fixed knife edge does. And this solution is much cheaper than a "motorized knife edge" ;-) Best regards Reinhard Am 22/10/2016 um 06:46 schrieb iangie: Dear Frantisek, >I have tried the 0.26 and 0.14° FDS, however a large "beam overflow" has >occurred. Moreover, the intensities of diffractions at higher angles are very >low in comparison to the data collected with ADS slits. [TW] At θ=1° , 0.26 and 0.14° FDS coresponding to ~39 and ~74 mm footprint on sample, respectively, which is much longer than your sample length 15mm. This beam overspill will induce air scattering which increases background at that angle. Using ADS, the sample volume illuminated is increasing with Sinθ dependance, therefore you observe "higher" peak intensity at high angle. At 2θ=2°, the knife edge hieght should be lower; At 2θ=50°, the knife edge height should be higher. Therefore, I recommanded you use Bruker's Motorised Knife Edge, which retracts itself in real time accoding to beam divergence and # of detector openning channels at each θ. Your LynxEye XE PSD should be able to opearte in Variable Detector Openning mode, which opens fewer channels at low angle and all channels at higher angle. You may want to try the scan type: "Coupled 2Theta/Theta (VDO)". However, the ultimate solution would be combining ADS, MKE, VDO together, which gives lowest possible background at low angle, ideal for recording clay basal reflections. -- Yours Sincerely, Dr. Tony Wang At 2016-10-21 21:59:23, "František Laufek" <mailto:frantisek.lau...@geology.cz> <frantisek.lau...@geology.cz> wrote: Dear all, I would like to ask you about your experience in collecting the XRD data from low angles (for me from 2° of 2Theta) to 50° 2Theta using the Bruker D8 Advance diffractometer (Bragg-Brentano geometry) with the Lynx Eye XE position sensitive detector. The studied samples are clay minerals and the main purpose of the task is qualitative and later (semi)quantitative phase analysis. I have fixed beam knife (=Anti-Scatter Screen) and ADS/FDS slits, 280 mm is the goniometer radius. The length of my samples is around 15 mm. After a few experiments and calculation, the optimal data collection strategy seems to be: - 10 mm automatic divergence slits (ADS), beam knife 2.5 mm above the sample (beam knife at this position does not interfere with the primary beam (to 50°) and still reduces the background at low angles). I have tried the 0.26 and 0.14° FDS, however a large "beam overflow" has occurred. Moreover, the intensities of diffractions at higher angles are very low in comparison to the data collected with ADS slits. Any suggestions are welcome. Frantisek Laufek Czech Geological Survey Prague Czech Republic ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <mailto:alan.he...@neutronoptics.com> <alan.he...@neutronoptics.com> Send commands to <mailto:lists...@ill.fr> <lists...@ill.fr> eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -- TU Bergakademie Freiberg Dr. R. Kleeberg Mineralogisches Labor Brennhausgasse 14 D-09596 Freiberg Tel. ++49 (0) 3731-39-3244 Fax. ++49 (0) 3731-39-3129
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