Towards Real-Time Active Collimation in Monolithic Arrays of Silicon Drift Detectors

We propose a study of active collimation for multi-element monolithic Silicon Drift Detectors (SDDs) based on real-time recognition of charge sharing events, exploiting key parameters such as the rise time of voltage step signals at the output of the charge-sensitive preamplifier (CSA), and the occurrence in a specific coincidence window of events generated in adjacent pixels.This method aims to overcome common issues of widely-employed mechanical collimation, especially in small-pixel-size detectors where a large part of the active area is covered by the physical collimator which becomes, moreover, quite complex to be manufactured for small apertures.Firstly, we performed measurements with a pulsed laser system providing a 4 μm spot size beam scanning the SDD surface with 10 μm steps, thanks to a 3-axis manual translating stage, to ensure a precise assessment of the charge sharing region.Afterward, we measured events generated by a 55 Fe X-ray source at the CSA output on an uncollimated 16-channel monolithic detector to assess the algorithm's capability of rejecting events with partial charge collection while retaining as many non-charge sharing events as possible. This method paves the way also for the possibility of summing partial events on adjacent pixels in order to recover as useful signals those charge sharing photons that would otherwise be discarded, thus maintaining the advantages of mechanical collimation while maximizing the active area.