Before you move on to multigrain indexing, you will need to know:

• what phases you are looking for,
• their crystal structures and cell parameters.

If you have a decent powder diffraction pattern to work with, you can try to do so with typical software people use in DAC experiments: dioptas, maud, etc.

There is a second option:

• collect diffraction peaks using peak-search,
• generate a 2-theta histogram of peaks.

This will be discussed below.

Generating a 2-theta histogram of peaks identified with a peak search has several advantages:

• most of the background signal (diamonds, shadows, etc) has been removed,
• a strong powder signal from the pressure medium will be partly removed,
• the signal from the sample you are trying to index is stronger,
• the histogram is based on the peak center of mass only, and hence removes the broadening due to grain size or internal strains.

Some drawbacks

• this is not a true powder diffraction pattern, peak broadening, in particular, is different,
• current easy-to-use versions do not sum intensities, but count the number of peaks for a given 2theta. The recovered intensity is proportional to the multiplicity, and not the structure factor. Diffraction intensities are messed up an can be used for structural refinements.

This can be done in ImageD11. Once calibrated for tilts, beam center, detector distance, etc, you can select

• Transformation → Load Filtered Peaks
• Transformation → Plot tth histogram

ImageD11 will ask for a number of bins (10000 is good) and you will get something like the screenshot below

Newer versions of ImageD11 (update February 2021) can then export this histogram using Transformation → Export tth histogram

It can be useful to load the histogram in MAUD. Remember, however, that this is not a true powder diffraction pattern,

• peak broadening, in particular, is different,
• current easy-to-use versions do not sum intensities, but count the number of peaks for a given 2theta. The recovered intensity is proportional to the multiplicity, and not the structure factor. Diffraction intensities are messed up an can be used for structural refinements.

To convert the histogram, use timelessTthHistogram2Maud from the TIMEleSS tools (see details below). Simply provide the detector distance (in mm), the name of the histogram file, and the name of the new ESG file, and you are good to go.

To load the data in MAUD

• Create a dataset with a simple diffraction instrument,
  • no intensity calibration,
  • flat image transmission, with the proper detector distance, no tilt, no beam center correction, nothing,
  • Synchrotron source with the proper wavelength,
  • Caglioti broadening, with asymmetry parameters set to 0,
• Load the ESG file

It should work…

timelessTthHistogram2Maud  -h
usage: timelessTthHistogram2Maud -d distance histogram.dat data.esg

Creates a MAUD ESG file from a text file with intensity vs. 2theta (in
degrees). This is part of the TIMEleSS project http://timeless.texture.rocks

positional arguments:
  txtdata               Name of file with intensity vs. 2theta
  output                Name of esg file

optional arguments:
  -h, --help            show this help message and exit
  -d DISTANCE, --distance DISTANCE
                        Detector distance (in mm, required)