Measurements with a hybrid detector prototype composed of a MOS CCD and a CZT spectrometer

Abstract

The scientific objectives of the future X-ray astronomy instruments require new type of focusing telescopes able to extend the observational range starting from 0.1 keV at least up to 100 keV to solve crucial question concerning the nature of the high energy emission. A challenging technology to extend the classical grazing incidence range to higher energy is today offered by the development of multilayer optics that are effective as X-ray concentrators between few keV up to 100 keV. A useful arrangement for this type of mission concept can foresee the soft (e.g. 0.1-10 keV) X-ray optics nested and coaxial with the hard-X mirrors. The focal plane of the telescope shall operate on a very wide band (from 0.1 to 100 keV) fulfilling at the best the different requirements of the two optics type in terms of detection efficiency, spatial resolution and spectroscopic performance. A solution for this kind of focal plane detector is given by a hybrid system with a soft X ray detector (e.g. CCD) in front and coaxial to a hard-X ray detector (e.g. Pixel CZT spectrometer). We have assembled a hybrid detector prototype using as soft X-ray detector a spare CMOS CDD22 of the EPIC/XMM instrument developed at Leicester University operating in the energy range of 0.2-10 keV and a CZT small pixel detector, capable of sensing X-rays or gamma rays in the energy range from 10 keV to 1.5 MeV. The MOS CCD22 is made of a p-type epitaxial silicon layer with a 40 μm square pixel, thickness of 80 μm and active area of 2.5x2.5 cm2. The substrate is 200 μm thick. The CZT sensor is a 4×4 multipixel paired with a 16 channel ASIC manufactured by eV Products. The thickness of the detector is 5 mm, while the lateral dimensions are 10.6×10.6 mm 2. The pixel size is 1.8 × 1.8 mm2 with a pitch of 2 mm. We report on the results of experimental measurements obtained with this hybrid detector prototype carried out at Leicester University.