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

Abstract

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.