Download Full Text - IAEA Publications - International Atomic Energy Agency

1. X RAY MICROPROBE
1.5 DATA ACQUISITION
motor to a convenient position, for example with cross in the center of display. Now,
reset x and y motors (to zero) by using Motor application’s system menu command.
Then enter (0,0) for the ‘motor referent position’ in the ‘Scan Properties… Optical’
dialog box. Note that it was not necessary to reset motors. In that case, you should
enter current x and y motor coordinates as the referent motors position.
Step 4: capillary position
Grab an image with using of the ‘Video… Image …Grab’ command. Note
that motors must be at position defined in the step three. Place cursor on the position
from the step one, read coordinates in millimeters and enter it as the ‘capillary
position’ in the ‘Scan Properties… Optical’ dialog box. Note if your cross is not
mounted on the holder together with sample than you can get picture of capillary
directly.
‰
Step 5: axis of rotation
Grab an image of the cross’s center with using of the ‘Video… Image… Grab’
command and then read position of the center in millimeters. It is recommended to
save this picture by ‘Video… Image… SaveAs’ command. Now, move motors to
zero, rotate them for 1800 (to 00), grab image and read the position in millimeters as
you did before. The average value of this two readings enter as ‘axis of rotation’ in
the ‘Scan Properties… Optical’ dialog box.
After this step you have all necessary information. However, the position of
capillary exit or beam may not be very precise established. Making an XRF image of
the cross’s center can check and correct this. Also, you can make similar correction on
the XRF image of the sample. However, it is recommended to proceed to the step six,
although not necessary.
‰
Step 6: correction of the capillary position and axis of rotation
This is described in six steps that follow bellow. Note, after the step four you
have already mounted cross and its image at 1800. In addition, the cross is at 00.
Therefore you can do there the step three and skip to the step five.
‰
Checking and correcting optical calibration (camera at 1800)
The error in position of the axis of rotation and capillary as well are the main
reasons for missing selected scan area. In the formula which program uses to move
the sample in the front of the capillary, the positions A and C of the axis and capillary
respectively, enter always as 2A-C. The precision of the calibration depends on the
overall value and not on the particular terms. To adjust the whole expression we can
alter, for example only position of the capillary. For this purpose, we should take XRF
image of a suitable object. This can be done by a few- micrometer thickness cross as
follows:
Step 1
Mount the cross and move motors on such a way that cross appears
somewhere around the center of the video image
‰
‰
36
Step 2
Grab video image with motors at 1800