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" <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
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