If you know the d-spacing, q-value, or 2theta of one or more Bragg rings from your calibration sample, then Datasqueeze can automatically find the detector parameters (with a little help). Make sure that you can identify which Bragg ring(s) on your false color image you will use for calibration, and that you know the relevant momentum transfer q, Bragg angle 2theta, or d-spacing d for each ring.
  • To start, click on "Start" underneath "Run Least-Squares Calibration Wizard". A new window should appear. Within this window, you follow instructions in a linear sequence. (You can always back up using the "Previous" button).
  • Verify that you have the correct beam wavelength entered, and retype into the box labeled "Lambda" if necessary.
  • Choose the number of Bragg rings that you will use to calibrate the instrument parameters. If you do not have an entire circle showing, you will need to use at least two. In general, the more rings you use, the better the fit, but also the longer it takes.
  • Next, you are asked if you already have the Bragg ring positions in a standard Bruker calibration file. These files are actually quite simple, and you can create one yourself using most standard text editors with the provided file (agbe.std) as a template. The first line is a title, and the each remaining line consists of a d-spacing (in angstroms) and an intensity (which isn't used for anything). Note however that this is one place where the number format is not locale-dependent; the d-spacings should all use the American format. That is, a d-spacing that is a little over 45 Angstroms should be written as 45.3 rather than 45,3. If you answer "Yes" to the query in this box then you will navigate to the file you want.
  • Enter the values of momentum transfer q, Bragg angle 2theta, or d-spacing d for each of the rings that you will use for calibration. If you have read in a calibration file, they will already be entered in editable boxes; if not, a default value will be entered. For the calibration to work properly you need rings, not sharp peaks from single crystals or fiber diffraction patterns, so your calibration material should be a powder.
  • Set the approximate position of the beam center. You an do this by clicking on the beam center position on the false color image, or by typing in the "X-Center" and "Y-Center" boxes.
  • For each ring, you will identify the feature in the data corresponding to the ring that will be analyzed. Drag the blue dots on the false color image so that the inner and outer rings span the Bragg ring of interest, just as if you were going to make a q-chi plot of that ring. This will tell Datasqueeze over what region it should do the least-squares fit. You want to make sure that the inner ring is everywhere at smaller radius, and the outer ring everywhere at larger radius, than the feature of interest, and also that no other strong features are included within that region.
  • Datasqueeze will now attempt to refine the detector parameters. Depending on the size of your image, and the reflection chosen, this may take some time. When it is done, the white box will display the results. If you wish you can cut-and-paste the information to another document. If the parameters look reasonable to you, and the rings on the false color image look centered, click "Next." Otherwise you can either back up using "Back" or cancel the whole process and revert to previous parameters using "Restore".
  • You are given the opportunity to save the d-spacing(s) you used in a calibration file. If you already got the parameters out of a .std file there is probably no point to this, but if you typed them in by hand then it may be convenient to save them for future use.
  • After the best calibration parameters (wavelength, q-range, tilt, etc.) have been determined, they can be saved in a file for subsequent use. Previously saved parameters can be retrieved in Batch mode using the "RETRIEVEINSTRUMENTPARAMETERS" command or in user mode using the Retrieve Parameters button in the Calibration window.