Monte Carlo study of a 3D CZT spectroscopic-imager for scattering polarimetry

The measurement of the polarisation of the high-energy emission from cosmic sources has now become a key observational parameter for understanding the production mechanisms and the geometry of the regions involved. Therefore, a mandatory requirement for new instrumentation in this energy range will be to provide high sensitivity for polarimetric measurements. For several years our group has studied the performance of CdTe/CZT pixel spectrometers as scattering polarimeters, however in order to achieve the sensitivities required by the next generation of instrumentation in the 100 keV to MeV band, a promising solution is now offered by the development of spectrometers capable of three-dimensional spatial resolution (i.e. 3D spectroscopic imager) to be used as the focal plane of new high energy focusing optics. In the framework of the study of a new spaceborne telescope based on a broad-band Laue lens (AHEAD 2020), we report on the results of a Monte Carlo study devoted to optimise the configuration of a 3D CZT detector for scattering polarimetry, i.e. to optimise its modulation factor (Q). In particular, we present results on the dependence of Q on the detector geometrical configurations (thickness and pixel/voxel scales), and from various event filters that can be implemented.