Imaging performance of a large-area Silicon Drift Detector for X-ray astronomy

Large-area multi-anode Silicon Drift Detectors (SDDs) have X-ray imaging and spectroscopic characteristics that make them extremely attractive in the perspective of their applications to the field of space astrophysics. We describe here the imaging performance of such a detector, originally developed for particle tracking in the ALICE experiment at LHC, as derived by laboratory measurements and Monte Carlo simulations. Despite an anode pitch of 294μm, we measured a position resolution as high as ∼20μm by charge weighting in the anode direction, for photon energies in the range 2–10 keV. These results are comparable to those obtained with the same detectors in particle tracking. Notwithstanding the 1-D nature of the devices, as far as their read-out is concerned, we envisaged an algorithm that exploits the charge diffusion to reconstruct the position of the photon absorption point also along the drift direction (that is, the one formally not position-sensitive). With the current set-up, the position resolution was measured as ∼3–5mm in the same energy range as above. Such 2-D imaging capability in a 1-D detector, although asymmetric, is highly useful in space applications, where the power and the complexity requested by a 2-D read-out system is sometimes unaffordable.