29 September 2004 Shielding of cosmic-ray-induced background in CCD detectors for x-ray astronomy
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Abstract
An active anticoincidence detector system for background reduction cannot be integrated in CCD detectors for X-ray astronomy. The background rate within an integration-readout interval would result in an unacceptable dead time of about 50% or more. Events of minimum ionizing particles can be discriminated in CCD detectors due to their high energy deposit and their image pattern. Events of X-rays or charged particles within the accepted energy band originating from cosmic ray interaction with the material surrounding the CCD cannot be distinguished from valid cosmic X-ray events and therefore contribute to the background noise. Graded-Z shielding is an efficient method to shift the energy of the locally produced X-rays to low energies. At low energies low-Z shielding material can be used, which rather produces Auger electrons than fluorescent X-rays. Low energy electrons can be stopped in the passivation layer of the CCD. Due to the low operating temperature of the CCD (~170 K) the shielding material has to have a similar thermal expansion coefficient as silicon. With regard to future X-ray missions the properties of several shielding materials like aluminium oxide, aluminium nitride, silicon nitride and boron carbide were investigated in more detail. The results are presented.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Elmar Pfeffermann, Elmar Pfeffermann, Peter Friedrich, Peter Friedrich, Michael Freyberg, Michael Freyberg, Guenther Kettenring, Guenther Kettenring, Ludwig Kraemer, Ludwig Kraemer, Norbert Meidinger, Norbert Meidinger, Peter Predehl, Peter Predehl, Lothar Strueder, Lothar Strueder, } "Shielding of cosmic-ray-induced background in CCD detectors for x-ray astronomy", Proc. SPIE 5501, High-Energy Detectors in Astronomy, (29 September 2004); doi: 10.1117/12.551262; https://doi.org/10.1117/12.551262
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