Nuclear instrumentation for a soft X-ray detection system on a small satellite, CATSAT

Nuclear instrumentation has been designed and tested for a large field of view soft X-ray sensor utilizing Si avalanche photodiodes (APDs). The instrument will be launched on a low cost satellite mission in mid 1998. The mission´s primary scientific objective is to determine the distance scale to the sources of cosmic gamma ray bursts by utilizing interstellar absorption effects observable in their X-ray emission at energies below 2 keV. The soft X-ray (SXR) sensor incorporates 7 identical panels, each with 16 APDs collectively collimated to a 1 steradian field of view. The SXR panels are radiatively cooled to -35 degrees C, and taken together, view a full hemisphere. The instrumentation for each of the sensors in the SXR detector includes a low noise, charge sensitive preamplifier/shaping amplifier and an analog electronics unit (AEU) containing a voltage amplifier, peak track and hold circuit, and threshold-timing logic. Each panel has an analog to digital interface (ADI) based on a field programmable gate array (FPGA), which controls the digitization of the event amplitudes, implements the in-flight calibration (IFC) for each APD, and coordinates the data output to and command input from the instrument CPU