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PostPosted: 09.12.2019, 18:54 
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Joined: 19.10.2019, 16:47
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The scanning method is the master method - still.
In front of the tube is a cross table with micrometer stepper, which moves a pinhole of about 10µm*10µm size across the area of the beam.

The picture shows the system (without the computer) in front of a 160kV X-ray tube.


The double slit collimator is made from four blocks of tungsten of 400x200x200mm^3 each, which have four 10µm thin 190x190mm^2 foils of steel (red color) to form in the center a hole of 10µm*10µm (best visible in Top View):


The collimator is moved step by step in both directions in front of the tube; this procedure used to take about one hours per focal spot. In the end an isodose contour plot was created.
Here is as example from a Philips MCN 451 X-ray tube the small focal spot:

The red X marks the maximum intensity (100% value); the following colored lines mark 10% less dose as further the line is away from the center; e.g. the outer red line is the 20% isodose contour line. The 10% threshold line to the background signal determines the nominal size which is here 1.487 x 1.448 mm^2 (width x length).

The Philips MCN 451 X-ray tube has two focal spots, the isodose contour plot of the large spot shows higher values:

and comes out with a focal spot size of 5.591 x 7.259 mm^2.

EN12543-1 recommends values for focal spot classes in [mm]:

and with this values the small focal spot of the MCN451 was nominated to 1.8mm and the large focal spot to 8mm.

Finally there is a bad news: There is no more equipment which can do this procedure; the last set of equipment at YXLON was scrapped in 2013 as there were no more spareparts available for the old evaluation PC. As far as I know it is the same with the equipment at BAM and also the Seifert/GE system shall be not more operable. In the conclusion this part shall be withdrawn in the next revision of EN12543 and Part 2 shall become the master.


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PostPosted: 13.12.2019, 13:29 
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Joined: 19.10.2019, 16:47
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Here is - for reference - the pinhole film-image of the small focal spot (the crossed wires were used to determine the center of the focal spot)


and here the pinhole film-image of the large focal spot (the crossed wires were used to determine the center of the focal spot)


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