Tube parameters
The X-ray machine is equipped with a standard General Electric "XRD" type glass tube with Tungsten target and four output windows.
Schematic cross section view of the used X-ray tube [1]
However, only two windows are accessible. The 'main' output window delivers a circular shaped fine focus beam of high intensity, as used during TID campaigns while the second window delivers a line-shaped beam of lower intensity, usually used for X-ray fluorescence applications. The output windows are made of 300 um thick Beryllium discs.
Schematic view of the dual beam output. Both under and angle of 6°.
After the X-rays exit the Be windows of the tube, they pass a filter wheel and a beam shutter which are part of the tube housing. There are two sets of filters and shutters, one for the fine focus - and one for the line focus beam. The available filter positions are {'0' (no filter), Fe, Mo, ...}. Since the beam has been calibrated using an external 150 um Al filter, the following measurements are taken with the filter wheel '0' position.
PICTURE
[1] University of Arizona, https://www.geo.arizona.edu/xtal/geos306/fall13-11.htm