Title:
High-accuracy calibration of the HXDS HPGe detector at the PTB radiometry
laboratory at BESSY
Authors:
Kraft, Stefan; Scholze, Frank; Thornagel, R.; Ulm, Gerhard; McDermott, Walter C.; Kellogg, Edwin M.
Affiliation:
AA(Physikalisch-Technische Bundesanstalt) AE(Smithsonian Astrophysical Observatory)
Publication:
Proc. SPIE Vol. 3114, p. 101-112, EUV, X-Ray, and Gamma-Ray Instrumentation
for Astronomy VIII, Oswald H. Siegmund; Mark A. Gummin; Eds.
Publication Date:
10/1997
Abstract:
The Smithsonian Astrophysical Observatory is performing the calibration of the AXAF High Resolution
Mirror Assembly (HRMA) at the Marshall Space Flight Center. In order to determine the absolute
incoming photon flux at the calibration facility a high purity germanium (HPGe) detector and an identical
spare detector have been chosen as flux monitor of the HRMA x-ray detection system (HXDS). The
detectors must thus be calibrated in the photon energy range between 700 eV and 10 keV. The
calibration and characterization of the detectors was performed at the radiometry laboratory of the
Physikalisch- Technische Bundesanstalt (PTB) at the electron storage ring BESSY. Two methods have
been applied for the determination of the detection efficiency. Firstly, the undispersed calculable
synchrotron radiation emitted by a bending magnet of the primary source standard BESSY has been
used. Secondly, the detection efficiency has been determined using monochromatized radiation and Si
photodiodes as transfer detector standards. The photodiodes have been calibrated with a relative
uncertainty of 0.5% in the photon energy range from 50 eV to 1500 eV against a cryogenic electrical
substitution radiometer which is a primary detector standard. It is shown that the determination of the
detection efficiency in the whole desired spectral range is possible with a relative uncertainty between
1% and 2%, even in the photon energy range where the detection efficiency is affected by the x-ray
absorption finestructures of the Al light blocking filter of the detector.