Version 14 (modified by toby, 12 years ago) (diff)


Integration of area detector data in GSAS-II

In this demo, data collected with a GE(?) area detector, intentionally tilted at 45 degrees, are used. Note that menu entries are listed in bold face below as Help/About? GSAS-II, which lists first the name of the menu (here "Help") and second the name of the entry in the menu (here "About GSAS-II").

Prerequisite: Calibration Demo

This assumes that an image data set has been read in and calibration results have been derived, see the Calibration Demo

Step 1: Clear calibration plot

Assuming the previous step was calibration, the image plot will show the located rings or the picked points. These are no longer needed. The Image Controls/Clear? Calibration menu entry removes these intermediate results, but does not clear the calibration results. Use of this menu item is not required, but does speed future display of results.

Step 2: Integration Settings

In the simplest case, all that is needed is to click on the "Do full integration?" checkbox and likely adjust the inner and outer 2-theta values with the two "Inner/Outer? 2-theta" controls. For the La_hex_+45deg-00015.tif image loaded before, good values are 0.5 and 7 degrees.

It is helpful to see the two-theta limits on the plot visually, while adjusting the two-theta range. This is done by clicking on the "Show integration limits?" checkbox. Note that inner limit is shown as a green ellipse and the outer is shown as a red ellipse (view). Note that changes are displayed only after pressing return, when numbers are placed in the boxes.

Other useful controls:

Azimuth offset: The image vertical axis (from the beam center, going upwards) is labeled with the azimuth value placed in the "Azimuth offset" box. This is usually zero.

Start/End? azimuth: The integration is started at the Start azimuth angle in the left box, and when the "Do full integration?" checkbox is not checked, then the integration will be run only to the maximum value specified. When the range is less than 360 degrees, the integration range will be shown (if selected) with the high and low limits plotted and only segments of the max and min ellipses drawn.

Number of 2-theta bins: The resulting 1-D powder pattern after integration will consist of this many points. This number should be on the order of the number of pixels in one direction (since resolution cannot be much better than this) or less, if instrumental resolution does not require that many points.

Number of azimuth bins: In cases where the diffraction experiment shows changes as a function of azimuthal angle, the integration can be performed as a function of angle. This number specifies the number of bins to use by azimuthal angle. The process of breaking up the integration in this way is sometimes called "caking" since the integration region grows with distance from the beam-center, with a shape like a slice of cake or pie. When more than one azimuthal bin is used, the regions are shown in the plot with dashed lines, when the Show integration limits?" checkbox is checked.

Step 3: Perform integration

Use the Image Operations/Integrate? image data menu item to start the integration. This will take at least a few seconds. If multiple images have been read in, the Integrate All menu item can be used. This is most useful when the "Use as Default" option is in use for one image.

At this point the data tree window will have a new entries for each azimuthal "slice" added to the data tree (view). Also, two plots are added to the plot window: One (with tab 2D Integration) shows the diffraction intensity as a function of both 2-theta and (when there is more than one azimuthal integration region) azimuthal angle (view); The other shows a conventional 1-D powder pattern(s) for each "slice" (view).

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