I welcome comments and opinions on the refinement of "instrumental parameters" during intensity data collection with a Bruker SMART Breeze CCD single crystal diffractometer. In APEX 2 software It is possible to refine the "instrumental parameters": unit cell; domain translation (x,y,z); domain orientation (omega, chi, phi); detector translation; detector pitch, roll, yaw; beam center (x,y); goniometer zeroes (omega, chi) About the unit cell refinement , there are an "initial" stage, and a final refinement stage, performed on all the collected frames. Which of the above listed "instrumental parameters" should be kept fixed, and which should instead be refined, and in which stage? Thanks in advance for your attention!
Good question. Unfortunately, no universal data reduction strategy exists: mostly, it depends on your sample and on the presence of systematic errors you have to deal with (diffuse scattering, twinning...). I suggest to have a look to
http://xray.tamu.edu/pdf/manuals/bruker_guide.pdf
and in particular to Chapt. 8 (Data reduction strategy). It makes reference to an old version of the software, but obviously the general ideas still hold true.
Hope this helps.
Dear Leonardo,
thanks for your message and for the guide, I shall read it willingly. If you are interested I shall post some considerations when I draw them.
Cheers Natale
Fit the intrumental parameters using a known standard (fixed unit cell). The dector distance and beam center are the first to refine. Also using a powder standard sample (Si, LaB6, Al2O3, etc) will make these 3 parameters quite easy to refine. Tilts can be refined after the beam center and detector distance converge. When you move to data on a sample where you want to refine the unit cell and orientation, the only instrument parameter that you may need to refine as well is the sample position. You may want to let the beam center refine as a final step in case there are any instabilitie with beam position over time.
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