Monte Carlo evaluation of a CZT 3D spectrometer suitable for a Hard X- and soft-gamma rays polarimetry balloon borne experiment

Today, the measurement of the polarization status of cosmic sources high-energy' emission, is recognized as a key observational parameter to understand the active production mechanism and its geometry. Therefore, a mandatory requirement for new instrumentations operating in this energ.-y range will be to provide high sensitivity for polarimetric measurements. In this framework, we have presented the concept of a small high-performance imaging spectrometer optimized for polarimetry between 100 and 600 keV suitable for a stratospheric balloon-borne payload and as a pathfinder for a future satellite mission. The detector with 3D spatial resolution is based on a CZT spectrometer in a highly segmented configuration designed to operate simultaneously as a high performance scattering polarimeter. Herein, we report results of a Monte Carlo study devoted to optimize the configuration of the detector for polarimetry with particular focus on event selection filter able to increase the polarimetric performance. This preliminary analysis shows that a procedure to optimize the polarization response of a 3D spectrometers should first of all determine the best tradeoff between the statistical significance and the quality of the modulation factor.