ESA Science & Technology - Geometry of the detectors in the HXI focal plane

The Hard X-ray Imager (HXI) is mounted beneath the WFI. It will extend the energy coverage up to 40 keV and enable simultaneous observations with both instruments. HXI should have an energy resolution better than 1 keV (FWHM) at 40 keV and cover a FOV of 12 × 12 arcmin².

The HXI detector is made up of three layers, 2-Silicon (Si) and 1 Cadmium Telluride (CdTe) detector, sitting back from the WFI plane by about 20, 25 and 30 mm, respectively. The 30 mm offset of the CdTe detector from the focal plane causes a PSF broadening of about 15 arcsec, assuming a mirror effective diameter of 1 m at 30 keV.

IXO was an L-class candidate mission in ESA's Cosmic Vision programme that was studied between 2007 and 2011.