WAXS processing and merging

Several SAXS beamlines use two (or more) detectors to collect different q regions. For example, the MacCHESS G1 beamline used dual Pilatus detectors to measure SAXS and WAXS from q ~0.008 – 0.75 Å-1. The SAXS detector has q ~< 0.25 Å-1 and the wide-angle scattering (WAXS) data has q >~ 0.25 Å-1. All of the data that you have been working with so far has been SAXS data. Some experiments can make use of the WAXS data. In this part of the tutorial you will learn the basics of processing it.

A video version of this tutorial is available:

The written version of the tutorial follows.

  1. Clear any data in RAW.
  2. Navigate to the standards_data and load the WAXS.cfg file.
  3. Plot the lysbuff2 PIL3 and lys2 PIL3 files. These are the images from the WAXS detector. Average these files and create a subtracted WAXS scattering profile.
    • Tip: Filenames should be lysbuff2_<stuff>_PIL3_<stuff>.tiff and lys2_<stuff>_PIL3_<stuff>.tiff.
  4. Load the saved subtracted SAXS scattering profile for the lysozyme standards data.
    • Note: You should have saved it in the standards_data folder, and it is likely named S_A_lys2_A9_17_001_0000.dat.
  5. Move the SAXS scattering profile you just loaded to the bottom plot by right clicking on it in the Profiles list and selecting “Move to bottom plot.”
  6. The WAXS data is not on the same scale as the SAXS data. For this data, the known scale factor to apply is 0.000014 to the WAXS data.
    • Note: The scale factor can be calculated as the ratio of solid angles subtended by the pixels on the SAXS and WAXS detectors, plus any scale factor for absolute calibration and normalization included for one curve but not the other.
  7. Star the WAXS data. Right click on the SAXS data and select Other Operations -> Merge. This will create a new merged scattering profile. The new file will have the prefix M_ to indicate it is a merged file.
    • Tip: If you can’t see it, that’s probably because it appeared on the upper plot, and is hidden by the very large intensities of the averaged WAXS files. Either try hiding those, or move the Merged curve to the lower plot.