  A flexible apparatus for calibration of the absolute flux at the focal plane
of the X-ray Source of a Powder Diffractometer, based on a fast scintillator
counter, is presented. The measured fluxes, depending on the high voltage on
the X-ray tube, were at the range 200 - 400 MHz, while an uncertainty in the
flux of the order of 5% has been estimated. We also applied this calibration
for radiation hardness study of a multichannel silicon microstrip X-Ray
detector.
