Measurement of transparency of thin beryllium X-ray windows by means of fluorescence lines produced by a Cm-244 alpha source

We present the results of the measurement of transparency of five round beryllium windows for the LEIPC (Low Energy Imaging Proportional Counter) of the Stellar X-ray Polarimeter (SXRP) experiment which will be flown on board the Spectrum X-gamma russian satellite. Each window was tested across its entire surface by using an X-ray fluorescence beam produced by a Cm-244 alpha source. We mapped the physical properties of the whole set in order either to verify the performance of the manufacturing method and to select the window having the highest counting rate and the most omogeneous transparency. This is crucial in order to both enhance the scientific capability of the experiment and to reduce the impact of possible systematic effects due to pointing instability which could occur during the observation of celestial sources.