Soft X-ray transmission of Contamination Blocking Filter for SXI onboard ASTRO-H

摘要

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 ~30nm thick Aluminum and ～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. ～70% at around 0.5 keV, and determined the thickness of Al and Polyimide to be 220 nm and ～50 nm, respectively. We will calculate the response function of SXI including these results.