Center the Sample: Your sample will be centered when the desired point/grains are near the cross hairs on the RAXVIDEO screen and in focus; Z is correct when the area of interest is in focus. The best technique for centering is to adjust the X and Y axes on the sample stage and rotate the PHI axis such that the “point of interest” stays centered at a point on the screen which should be near the cross hairs (because the microscope-telescope is a fragile device, the cross hairs will wander a bit from the goniometer center). First adjust X, Y, and Z axes at the lower magnification needed to see your sample, THEN increase the magnification to maximum and readjust, THEN rotate the PHI axis by 180 to 270 degrees, back and forth getting your “point of interest” to “stay still.” The focus should be set at the center of the “point of interest” but if you rotate OMEGA back to 0 degrees, the center is at the same point on the RAXVIDEO screen where the “stay still” position is.
Low Magnification Maximum Magnification
NOTE: Different settings of sample holders and reflection-vs.-transmission conditions can limit the OMEGA Range accessible. This is especially true in the relationship of OMEGA with PHI.
Measurements on “glass fiber mounted” samples:
Fiber mounted samples are considered small and transparent to X-rays.
Install Collimator: A long collimator should be placed on the instrument, choosing a collimator diameter appropriate to the size of the sample on the fiber – generally the 0.8 mm collimator is good for larger samples and the 0.1 mm Monocap collimator for smaller samples (the Monocap collimator costs over $10,000 – be very careful with it and always return it too the wooden case when finished or removing it).
Attach BEAM STOP: Attach the short beam stop if you will not need to move Omega above 60 degrees, otherwise attach the long beam stop.
Set Attachment Stage and Sample Holder Conditions: Two buttons on the Goniometer Setting of the RINT/Rapid screen marked CHANGE must be set for your experiment. Different Mounting techniques and specimen aspect ratios require limits to the ranges of OMEGA and PHI.
Attachment Stage: Set to “Goniometer” if you need a larger range of Omega otherwise set to “Manual-XY-stage.” “Goniometer” permits –70<ω<150, whereas “Manual XY” permits ‑15<ω<150, but OMEGA should never be set lower than –20 because of limits set on this unit.
Sample Holder: Set to “Transmission.” With “Goniometer” this permits –180<φ<360 whereas with “Manual XY” –20<φ<60. To produce diffractions suitable to interpret a few crystals as a powder pattern, you need to rotate PHI by 180° if not 360°, thus the desirability to set the sample holder as a Goniometer Head rather than as the XY stage. But Keep to the limits shown below.