A CZT 3D imaging spectrometer prototype with digital readout for high energy astronomy

The scientific challenges still open in hard X-rays and γ-rays astronomy require the development of new instrumentation able to overcome the sensitivity limits of the present one. Among the technologies currently under study to cover the energy range between several tens of keV and one MeV, the development of telescopes equipped with broadband Laue lenses associated with focal planes with high spectroscopic and imaging performance represents an extremely promising solution. With this perspective, we report on the development and the first spectroscopic characterisation results of an X/γ rays detection system (10-1000 keV) based on CZT spectrometers with spatial resolution in three dimensions (3D) and a digital acquisition electronic chain suitable to build high-performance focal planes. The final prototype will be made by packing four sensors. Each sensor is realised using a single spectroscopic grade CZT crystal with dimensions of ∼20×20×6 mm3, on which the anode strips are realised orthogonally to the cathode ones. The anode structure consists of 12 collecting anodes with a pitch of 1.6 mm and three drift strips between each pair of anodes, while the cathode side is segmented into ten strips with a pitch of 2 mm, orthogonal to anode side strips. The detector front-end electronics is based on custom-designed low noise charge sensitive preamplifiers (CSP). The CZT sensor induces the charge pulses on the electrodes, then they are read by a multichannel Digital Pulse Processing system based on FPGA through its readout front-end. The results obtained with both standard spectroscopic chains and the analysis of digitised pre-amplified signals confirm the expected performances in terms of spectroscopy (<1% FWHM at 662 keV).