Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004spie.5501..304p&link_type=abstract
High-Energy Detectors in Astronomy. Edited by Holland, Andrew D. Proceedings of the SPIE, Volume 5501, pp. 304-311 (2004).
Astronomy and Astrophysics
Astronomy
2
Scientific paper
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.
Freyberg Michael
Friedrich Peter
Kettenring Günther
Krämer Ludwig
Meidinger Norbert
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