Design and optimization around 1 MeV of a calorimeter for a cubesat mission

The next generation of space observatories for gamma-ray astrophysics will focus on the energy range around 1 MeV, where Compton scattering is the dominant interaction mechanism. The best instrument to date in this range, COMPTEL, the Compton Telescope on-board the Compton Gamma-Ray Observatory (CGRO), flew in the 1990's but with a technology dating more than a decade earlier. New observatories will use robust and reliable detector technologies, such as Silicon detectors, building on the heritage of current space instruments such as Fermi-LAT. Given the huge leap in technology, performance is expected to improve at least an order of magnitude with respect to COMPTEL, but several issues complicate this optimistic picture. The large external background, an internal background due to material activation, the complexity of Compton track reconstruction and event analysis, all require a careful optimization of instrument design and operation. In the MeV regime, the performance of the calorimeter becomes a key ingredient in the design of the observatory. Energetic and spatial resolution both impact heavily on the reconstruction of the Compton event, and thus on the overall acceptance and on the background rejection capabilities. Available software libraries allow for a detailed simulation of the detector, to quantify the performance and evaluate the best choice of the detector design. Size and granularity of the crystals, readout electronics, power consumption, must be optimized with a systematic investigation of the parameter space.