Polarimetry with a Multi-layer CdTe Prototype for Soft Gamma-ray Astrophysics

The development of a new generation of soft gamma-ray telescopes should allow polarimetric measurements of astrophysical sources to be associated with the results from spectroscopy and imaging due to the promising developments in polarimetry achieved over the last decade. In this perspective, the advanced surveyor of transient events and nuclear astrophysics mission which includes a narrow field telescope (NFT) that comprises a wide band Laue lens (60–600 keV) associated with a high performance thick and stacked CdZnTe focal plane operating as spectrometer, imager, and scattering polarimeter has been submitted for the ESA Voyage 2050 long term scientific planning preparation. In this context, and with the aim of optimizing the focal plane configuration of an instrument such as NFT, several studies are underway. In particular, with this work we study some performance issues such as polarimeters of segmented semiconductor detectors at room temperature, such as CdZnTe and cadmium telluride (CdTe), by means of a prototype based on two planar CdTe spectroimagers operating in coincidence. The two CdTe detectors are 2-mm-thick crystals with the anode segmented in $8\times8$ pixels with 2-mm pitch. This prototype configuration allows the Compton polarimetric performance of a spectroimager to be assessed by changing the distance between the two detection layers while operating in the 100–600-keV energy range, thereby allowing the analysis of Compton polarimetry 3-D dependence. The results obtained provide relevant input to the design of large sensitive volume multilayer and 3-D sensitive focal planes.