Soft x-ray transmission of contamination blocking filter for SXI onboard ASTRO-H

X-ray CCD operated onboard satellite are contaminated by outgas from organic material used in satellites. This contamination causes a significant reduction in the detection sensitivity of X-ray detectors. In order to prevent such contamination to the Back-IlluminatedCCD (BI-CCD) of the Soft X-ray Imager (SXI) onboard ASTRO-H, we have developed a Contamination Blocking Filter (CBF), which consists of similar to 30nm thick Aluminum and similar to 200nm thick Polyimide. The CBF is be placed on the top of the CCD camera hood and is required to have a high X-ray transmission in order to take advantage of the high detection efficiency of BI-CCD. We measured the X-ray transmission of three fight candidates of the CBF last October at the SPring-8 and obtained the X-ray transmission of three CBFs in the soft X-ray energy from 0.2 to 1.8 keV which covers the absorption edges around C-K, N-K, O-K, and Al-K including X-ray absorption fine structure (XAFS). In these measurements, we found three CBFs have high X-ray transmission below 2ke V, e.g. similar to 70% at around 0.5 keV, and determined the thickness of Al and Polyimide to be 220 nm and similar to 50 nm, respectively. We will calculate the response function of SXI including these results.