Charge Sharing Assessment and Active Collimation in Monolithic Arrays of Silicon Drift Detectors

Abstract

Charge sharing (CS) between pixels is a significant concern in X-ray spectroscopy detectors based on monolithic arrays of silicon drift detectors (SDDs) when a photon is absorbed near a pixel edge. Traditional mechanical collimation mitigates CS but decreases the active area of the detector. This is particularly true for small-pixel detectors, where the mechanical collimator shields a significant portion of the active area and, moreover, becomes quite complex to be manufactured for small apertures. In this work, we carry out a study of CS in SDDs and introduce active collimation as an alternative to mechanical collimation, leveraging key parameters of signals at the output of the charge-sensitive amplifier (CSA), to identify CS events occurring within a defined coincidence window (CW) in neighboring pixels. To validate the technique, we first conducted a quantitative assessment of the impact of CS on a 16-element monolithic SDD module with 2-mm-side square pixels using a focused pulsed laser. We then tested an active collimation algorithm on this detector configuration during a spectroscopic measurement with an uncollimated 55Fe source, demonstrating its capability in recovering CS events and reconstructing them as Mn-K $\alpha $ peak events. This active collimation approach, in contrast to mechanical collimation, not only enhances the effective active area while achieving a substantial reduction in the background continuum of the spectrum, but also recovers information inevitably lost in uncollimated detectors due to intrinsic CS effects.