AXAF HXDS germanium solid state detectors

The design, calibration, and performance of the high purity germanium (HPGe) solid state detectors (SSDs) used in the calibration of the Advanced X-ray Astrophysics Facility high resolution mirror assembly (HRMA) is discussed. The focal plane SSD was used with various apertures to measure the point response function, as well as the effective area of the mirror. The good energy resolution of the detector allowed the effective energy of the mirrors to be measured with a single exposure using a continuum source. The energy resolution was also exploited in measuring the molecular contamination on the mirror surfaces. The SSDs are the transfer detector standards for the HRMA calibration over the energy range from 700 eV to 10 keV. The calibration of the SSDs was performed mostly at the PTB radiometry laboratory using the electron storage ring BESSY. The spectral and spacial distribution of the undispersed synchrotron radiation can be calculated from first principles using the Schwinger Equation. With the electron storage ring being run in a reduced current mode of a few electrons, uncertainties in the calculated flux are below 1%. A comparison of the measured and calculated flux made it possible to determine the detector efficiency with an uncertainty of typically 1%. Electronic effects such as pile- up, count rate linearity and deadtime have been investigated.