ON THE X-RAY TRANSMISSION PROPERTIES OF MULTILAYER WINDOWS

The X-ray transmission properties of the multilayer X-ray entrance window of the Low Energy Gas Scintillation Proportional Counter (LE-GSPC) being developed for the SAX X-ray Astronomy Satellite, were measured as a function of X-ray energy and position in the 100-1800 eV region using monochromatic synchrotron radiation. Particular attention was paid to avoiding interference effects with the fine grid and strongback, supporting the nominally 1.25 mum thick window. The window is made gas tight and atomic oxygen resistant by several Al/AlN multilayers. Since the layer thicknesses are comparable to the wavelengths of the X-ray region covered by the LE-GSPC, interference effects were not excluded a priori. The X-ray transmission revealed complex structures, particularly around the absorption edges. Such structures and observed position dependences demonstrate the necessity to calibrate these windows over a fine energy grid prior to their incorporation into any flight detector.