Ageing of Ge/Si and CZT Samples for Sensors and Laue Lenses of Future Gamma-ray Astrophysics Telescopes

The analysis of LEO (Low Earth Orbit) environment effects on the detection medium materials and/or focusing lens materials for future gamma-ray telescopes is crucial to design a high-energy astrophysics’ space mission. We intend to investigate the radiation damage and ageing, and their effects on the operational performances in real in-orbit conditions, allowing us to forecast the effective lifetime of the scientific instruments in space. The proposed materials to study are CZT, Ge and Si crystals, since they are a relevant part of gamma-ray systems of All-sky Medium Energy Gamma-ray Observatory (AMEGO) and of Advanced Surveyor of Transient Events and Nuclear Astrophysics (ASTENA) missions. CZT based sensors will be used in the calorimeter module of AMEGO as well as focal plane spectroscopic imager of the Narrow Field Telescope (NFT) on board ASTENA which is based on a Laue lens system. Laue optics based in Ge and Si bent crystals are currently under development, being mandatory to test the impact of the LEO environment on these systems in order to verify the stability of their curvature radius and diffraction efficiency. In the NFT optics the material thicknesses vary from 1 to 5 mm according to the working energy passband. Concerning the samples of CZT sensors, small crystals (8.9×4.3 mm2 in area; 2-5 mm thickness) with metallized (Au) and passivated surfaces will be used. The experiment will allow verifying if and how fundamental electrical and electronic properties (e.g., bulk and surface currents, and charge transport properties) change due to space environment exposure, affecting the final detectors’ spectroscopic and imaging performances.