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Sample‐detector distance calibration

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etortorici edited this page May 16, 2024 · 1 revision

Silver behenate exposure

Silver behenate (AgBh) is a well characterized material that can be used to determine the sample-detector distance.

AgBh can be prepared in a capillary and placed at the same distance as your sample by either placing it next to your sample's capillary (in the case of WAXS or SAXS) or placed horizontally along the black line of the GIWAXS stage.

Whatever stitch size you use for your sample, you should use for the AgBh exposure. An exposure time of 5-10 minutes per stitch should be plenty of time to get good counts.

pyFAI calibration

pyFAI has a calibration GUI that can be used to fit the AgBh data for the sample-detector distance and beam center. The gui can be launched from the Anaconda prompt with

pyFAI-calib2

  • In the toolbar, select "Y" icon and select "Orient Y-axis downward"
  • In the right panel:
    • Set wavelength to 1.54185 Angstrom
    • Select AgBh from calibrants
    • Select the ... button under "Detector" and then load from file
      • the install should save .h5 files for each eiger_stitch size in "Documents/XRDpy/detectors/". Select the file matching the calibration's stitch size.
    • Designate the calibration TIFF (this is the picture produced by the AgBh exposure).
    • Ignore the mask option for now.
  • Press "Next" to get to the mask making step. Use the polygon tool to draw mask around the beam stop. The circle tool can also be used to mask the first peak since it is partially covered by the beam stop. Once a mask is made, Press "Next to get to the ring selection tool.
  • Select peaks 1-5 (or 2-5 if you masked the first peak).
    • By default, the green + should be selected: this means that the peak indicator will increment every time you select a peak.
    • If you masked the first peak, click the green + and change the peak indicator to 2, select the second peak, and then reselect the green + so that it will automatically increment with each peak selection.
  • Select "Next" to begin fitting. Select the "SAXS constraints" and then fit.
  • Save the PONI file as "cal.poni" with your data.

The PONI file contains all the relevant parameters (except the exposure time, incident angle, and the sample tilt angle).

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