Powder Ring Pattern

The Powder Ring Pattern window opens with a ring pattern plotted with the current crystal file data and microscope parameters. The controls permit to change several parameters like accelerating voltage, camera length or to load other crystal files for rapid matching.

Figure 1 shows the ring pattern window. The tool bar contains tool buttons to:

Print the window.
Save the drawing.
Open an experimental pattern.
Magnifier glass.
Process the background image.
Show parameters Keeper.
Show this help file.

Figure 1 Calculated CdSe powder ring pattern window.

The Controls pane (Fig. 2a) contains allows to change the line shape, to introduce the Blackman correction to the lines intensity, to modify the microscope parameters and a table of structures to use for the lines plot.

The processing pane (Fig. 2b) does (image processing) on the background image.


Figure 2a Controls pane.	Figure 2b Processing pane.

The tool buttons of the crystals table allow for:

Adding a crystal.
Adding all crystals of the current directory.
Suppressing a crystal.
Deleting all crystals.

Only the powder lines of the crystals checked in the table are plotted.

The calibration, camera length, scale and zoom controls, all modifying the dimension of the drawing can be freezed. This allows to calibrate the drawing using a powder pattern of a known crystal (Figures 3a, 3b). The line shape is modified using the crystal diameter slider (Fig. 3c).


Figure 3a Calibration pane.	Figure 3b Microscope pane.	Figure 3b Powder pane.

Figure 4 Calculated CdSe powder pattern and rings.

After loading an experimental pattern the center of the calculated ring pattern can be moved to the center of the experimental one by dragging the green cross at the center . The integrated ring intensity is plotted with either a gaussian or lorentzian line shape (i.e. I_hkl/d_hkl). The width of the line depends on the crystal size following a gaussian approximation of the sinc² law. (Fig. 4).

Figure 5 Match with CdTe is not convincing.

Figure 6 Comparison of CdSe and CdTe.

A table of the reflections is available with the structure factor dialogue (Fig. 4).

Figure 7 Table of the CdSe reflections.

Two possibilities:

Select with the mouse the green cross at the middle of the pattern and move the cross to translate it.
Use the Alt, Ctrl and Shift keys together with the up, down, left, right arrows to move the pattern. Any combination of Alt, Ctrl and Shift is possible (depending on the operating system). The translation speed is fastest with Alt+Ctrl+Shift.